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linux-zen-server/kernel/rcu/tree.c

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2023-08-30 17:53:23 +02:00
// SPDX-License-Identifier: GPL-2.0+
/*
* Read-Copy Update mechanism for mutual exclusion (tree-based version)
*
* Copyright IBM Corporation, 2008
*
* Authors: Dipankar Sarma <dipankar@in.ibm.com>
* Manfred Spraul <manfred@colorfullife.com>
* Paul E. McKenney <paulmck@linux.ibm.com>
*
* Based on the original work by Paul McKenney <paulmck@linux.ibm.com>
* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
*
* For detailed explanation of Read-Copy Update mechanism see -
* Documentation/RCU
*/
#define pr_fmt(fmt) "rcu: " fmt
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/rcupdate_wait.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/nmi.h>
#include <linux/atomic.h>
#include <linux/bitops.h>
#include <linux/export.h>
#include <linux/completion.h>
#include <linux/moduleparam.h>
#include <linux/panic.h>
#include <linux/panic_notifier.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/mutex.h>
#include <linux/time.h>
#include <linux/kernel_stat.h>
#include <linux/wait.h>
#include <linux/kthread.h>
#include <uapi/linux/sched/types.h>
#include <linux/prefetch.h>
#include <linux/delay.h>
#include <linux/random.h>
#include <linux/trace_events.h>
#include <linux/suspend.h>
#include <linux/ftrace.h>
#include <linux/tick.h>
#include <linux/sysrq.h>
#include <linux/kprobes.h>
#include <linux/gfp.h>
#include <linux/oom.h>
#include <linux/smpboot.h>
#include <linux/jiffies.h>
#include <linux/slab.h>
#include <linux/sched/isolation.h>
#include <linux/sched/clock.h>
#include <linux/vmalloc.h>
#include <linux/mm.h>
#include <linux/kasan.h>
#include <linux/context_tracking.h>
#include "../time/tick-internal.h"
#include "tree.h"
#include "rcu.h"
#ifdef MODULE_PARAM_PREFIX
#undef MODULE_PARAM_PREFIX
#endif
#define MODULE_PARAM_PREFIX "rcutree."
/* Data structures. */
static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
.gpwrap = true,
#ifdef CONFIG_RCU_NOCB_CPU
.cblist.flags = SEGCBLIST_RCU_CORE,
#endif
};
static struct rcu_state rcu_state = {
.level = { &rcu_state.node[0] },
.gp_state = RCU_GP_IDLE,
.gp_seq = (0UL - 300UL) << RCU_SEQ_CTR_SHIFT,
.barrier_mutex = __MUTEX_INITIALIZER(rcu_state.barrier_mutex),
.barrier_lock = __RAW_SPIN_LOCK_UNLOCKED(rcu_state.barrier_lock),
.name = RCU_NAME,
.abbr = RCU_ABBR,
.exp_mutex = __MUTEX_INITIALIZER(rcu_state.exp_mutex),
.exp_wake_mutex = __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex),
.ofl_lock = __ARCH_SPIN_LOCK_UNLOCKED,
};
/* Dump rcu_node combining tree at boot to verify correct setup. */
static bool dump_tree;
module_param(dump_tree, bool, 0444);
/* By default, use RCU_SOFTIRQ instead of rcuc kthreads. */
static bool use_softirq = !IS_ENABLED(CONFIG_PREEMPT_RT);
#ifndef CONFIG_PREEMPT_RT
module_param(use_softirq, bool, 0444);
#endif
/* Control rcu_node-tree auto-balancing at boot time. */
static bool rcu_fanout_exact;
module_param(rcu_fanout_exact, bool, 0444);
/* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
module_param(rcu_fanout_leaf, int, 0444);
int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
/* Number of rcu_nodes at specified level. */
int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
/*
* The rcu_scheduler_active variable is initialized to the value
* RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the
* first task is spawned. So when this variable is RCU_SCHEDULER_INACTIVE,
* RCU can assume that there is but one task, allowing RCU to (for example)
* optimize synchronize_rcu() to a simple barrier(). When this variable
* is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required
* to detect real grace periods. This variable is also used to suppress
* boot-time false positives from lockdep-RCU error checking. Finally, it
* transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU
* is fully initialized, including all of its kthreads having been spawned.
*/
int rcu_scheduler_active __read_mostly;
EXPORT_SYMBOL_GPL(rcu_scheduler_active);
/*
* The rcu_scheduler_fully_active variable transitions from zero to one
* during the early_initcall() processing, which is after the scheduler
* is capable of creating new tasks. So RCU processing (for example,
* creating tasks for RCU priority boosting) must be delayed until after
* rcu_scheduler_fully_active transitions from zero to one. We also
* currently delay invocation of any RCU callbacks until after this point.
*
* It might later prove better for people registering RCU callbacks during
* early boot to take responsibility for these callbacks, but one step at
* a time.
*/
static int rcu_scheduler_fully_active __read_mostly;
static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
unsigned long gps, unsigned long flags);
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
static void invoke_rcu_core(void);
static void rcu_report_exp_rdp(struct rcu_data *rdp);
static void sync_sched_exp_online_cleanup(int cpu);
static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp);
static bool rcu_rdp_is_offloaded(struct rcu_data *rdp);
static bool rcu_rdp_cpu_online(struct rcu_data *rdp);
static bool rcu_init_invoked(void);
static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
/*
* rcuc/rcub/rcuop kthread realtime priority. The "rcuop"
* real-time priority(enabling/disabling) is controlled by
* the extra CONFIG_RCU_NOCB_CPU_CB_BOOST configuration.
*/
static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
module_param(kthread_prio, int, 0444);
/* Delay in jiffies for grace-period initialization delays, debug only. */
static int gp_preinit_delay;
module_param(gp_preinit_delay, int, 0444);
static int gp_init_delay;
module_param(gp_init_delay, int, 0444);
static int gp_cleanup_delay;
module_param(gp_cleanup_delay, int, 0444);
// Add delay to rcu_read_unlock() for strict grace periods.
static int rcu_unlock_delay;
#ifdef CONFIG_RCU_STRICT_GRACE_PERIOD
module_param(rcu_unlock_delay, int, 0444);
#endif
/*
* This rcu parameter is runtime-read-only. It reflects
* a minimum allowed number of objects which can be cached
* per-CPU. Object size is equal to one page. This value
* can be changed at boot time.
*/
static int rcu_min_cached_objs = 5;
module_param(rcu_min_cached_objs, int, 0444);
// A page shrinker can ask for pages to be freed to make them
// available for other parts of the system. This usually happens
// under low memory conditions, and in that case we should also
// defer page-cache filling for a short time period.
//
// The default value is 5 seconds, which is long enough to reduce
// interference with the shrinker while it asks other systems to
// drain their caches.
static int rcu_delay_page_cache_fill_msec = 5000;
module_param(rcu_delay_page_cache_fill_msec, int, 0444);
/* Retrieve RCU kthreads priority for rcutorture */
int rcu_get_gp_kthreads_prio(void)
{
return kthread_prio;
}
EXPORT_SYMBOL_GPL(rcu_get_gp_kthreads_prio);
/*
* Number of grace periods between delays, normalized by the duration of
* the delay. The longer the delay, the more the grace periods between
* each delay. The reason for this normalization is that it means that,
* for non-zero delays, the overall slowdown of grace periods is constant
* regardless of the duration of the delay. This arrangement balances
* the need for long delays to increase some race probabilities with the
* need for fast grace periods to increase other race probabilities.
*/
#define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays for debugging. */
/*
* Return true if an RCU grace period is in progress. The READ_ONCE()s
* permit this function to be invoked without holding the root rcu_node
* structure's ->lock, but of course results can be subject to change.
*/
static int rcu_gp_in_progress(void)
{
return rcu_seq_state(rcu_seq_current(&rcu_state.gp_seq));
}
/*
* Return the number of callbacks queued on the specified CPU.
* Handles both the nocbs and normal cases.
*/
static long rcu_get_n_cbs_cpu(int cpu)
{
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
if (rcu_segcblist_is_enabled(&rdp->cblist))
return rcu_segcblist_n_cbs(&rdp->cblist);
return 0;
}
void rcu_softirq_qs(void)
{
rcu_qs();
rcu_preempt_deferred_qs(current);
rcu_tasks_qs(current, false);
}
/*
* Reset the current CPU's ->dynticks counter to indicate that the
* newly onlined CPU is no longer in an extended quiescent state.
* This will either leave the counter unchanged, or increment it
* to the next non-quiescent value.
*
* The non-atomic test/increment sequence works because the upper bits
* of the ->dynticks counter are manipulated only by the corresponding CPU,
* or when the corresponding CPU is offline.
*/
static void rcu_dynticks_eqs_online(void)
{
if (ct_dynticks() & RCU_DYNTICKS_IDX)
return;
ct_state_inc(RCU_DYNTICKS_IDX);
}
/*
* Snapshot the ->dynticks counter with full ordering so as to allow
* stable comparison of this counter with past and future snapshots.
*/
static int rcu_dynticks_snap(int cpu)
{
smp_mb(); // Fundamental RCU ordering guarantee.
return ct_dynticks_cpu_acquire(cpu);
}
/*
* Return true if the snapshot returned from rcu_dynticks_snap()
* indicates that RCU is in an extended quiescent state.
*/
static bool rcu_dynticks_in_eqs(int snap)
{
return !(snap & RCU_DYNTICKS_IDX);
}
/*
* Return true if the CPU corresponding to the specified rcu_data
* structure has spent some time in an extended quiescent state since
* rcu_dynticks_snap() returned the specified snapshot.
*/
static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap)
{
return snap != rcu_dynticks_snap(rdp->cpu);
}
/*
* Return true if the referenced integer is zero while the specified
* CPU remains within a single extended quiescent state.
*/
bool rcu_dynticks_zero_in_eqs(int cpu, int *vp)
{
int snap;
// If not quiescent, force back to earlier extended quiescent state.
snap = ct_dynticks_cpu(cpu) & ~RCU_DYNTICKS_IDX;
smp_rmb(); // Order ->dynticks and *vp reads.
if (READ_ONCE(*vp))
return false; // Non-zero, so report failure;
smp_rmb(); // Order *vp read and ->dynticks re-read.
// If still in the same extended quiescent state, we are good!
return snap == ct_dynticks_cpu(cpu);
}
/*
* Let the RCU core know that this CPU has gone through the scheduler,
* which is a quiescent state. This is called when the need for a
* quiescent state is urgent, so we burn an atomic operation and full
* memory barriers to let the RCU core know about it, regardless of what
* this CPU might (or might not) do in the near future.
*
* We inform the RCU core by emulating a zero-duration dyntick-idle period.
*
* The caller must have disabled interrupts and must not be idle.
*/
notrace void rcu_momentary_dyntick_idle(void)
{
int seq;
raw_cpu_write(rcu_data.rcu_need_heavy_qs, false);
seq = ct_state_inc(2 * RCU_DYNTICKS_IDX);
/* It is illegal to call this from idle state. */
WARN_ON_ONCE(!(seq & RCU_DYNTICKS_IDX));
rcu_preempt_deferred_qs(current);
}
EXPORT_SYMBOL_GPL(rcu_momentary_dyntick_idle);
/**
* rcu_is_cpu_rrupt_from_idle - see if 'interrupted' from idle
*
* If the current CPU is idle and running at a first-level (not nested)
* interrupt, or directly, from idle, return true.
*
* The caller must have at least disabled IRQs.
*/
static int rcu_is_cpu_rrupt_from_idle(void)
{
long nesting;
/*
* Usually called from the tick; but also used from smp_function_call()
* for expedited grace periods. This latter can result in running from
* the idle task, instead of an actual IPI.
*/
lockdep_assert_irqs_disabled();
/* Check for counter underflows */
RCU_LOCKDEP_WARN(ct_dynticks_nesting() < 0,
"RCU dynticks_nesting counter underflow!");
RCU_LOCKDEP_WARN(ct_dynticks_nmi_nesting() <= 0,
"RCU dynticks_nmi_nesting counter underflow/zero!");
/* Are we at first interrupt nesting level? */
nesting = ct_dynticks_nmi_nesting();
if (nesting > 1)
return false;
/*
* If we're not in an interrupt, we must be in the idle task!
*/
WARN_ON_ONCE(!nesting && !is_idle_task(current));
/* Does CPU appear to be idle from an RCU standpoint? */
return ct_dynticks_nesting() == 0;
}
#define DEFAULT_RCU_BLIMIT (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 1000 : 10)
// Maximum callbacks per rcu_do_batch ...
#define DEFAULT_MAX_RCU_BLIMIT 10000 // ... even during callback flood.
static long blimit = DEFAULT_RCU_BLIMIT;
#define DEFAULT_RCU_QHIMARK 10000 // If this many pending, ignore blimit.
static long qhimark = DEFAULT_RCU_QHIMARK;
#define DEFAULT_RCU_QLOMARK 100 // Once only this many pending, use blimit.
static long qlowmark = DEFAULT_RCU_QLOMARK;
#define DEFAULT_RCU_QOVLD_MULT 2
#define DEFAULT_RCU_QOVLD (DEFAULT_RCU_QOVLD_MULT * DEFAULT_RCU_QHIMARK)
static long qovld = DEFAULT_RCU_QOVLD; // If this many pending, hammer QS.
static long qovld_calc = -1; // No pre-initialization lock acquisitions!
module_param(blimit, long, 0444);
module_param(qhimark, long, 0444);
module_param(qlowmark, long, 0444);
module_param(qovld, long, 0444);
static ulong jiffies_till_first_fqs = IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 0 : ULONG_MAX;
static ulong jiffies_till_next_fqs = ULONG_MAX;
static bool rcu_kick_kthreads;
static int rcu_divisor = 7;
module_param(rcu_divisor, int, 0644);
/* Force an exit from rcu_do_batch() after 3 milliseconds. */
static long rcu_resched_ns = 3 * NSEC_PER_MSEC;
module_param(rcu_resched_ns, long, 0644);
/*
* How long the grace period must be before we start recruiting
* quiescent-state help from rcu_note_context_switch().
*/
static ulong jiffies_till_sched_qs = ULONG_MAX;
module_param(jiffies_till_sched_qs, ulong, 0444);
static ulong jiffies_to_sched_qs; /* See adjust_jiffies_till_sched_qs(). */
module_param(jiffies_to_sched_qs, ulong, 0444); /* Display only! */
/*
* Make sure that we give the grace-period kthread time to detect any
* idle CPUs before taking active measures to force quiescent states.
* However, don't go below 100 milliseconds, adjusted upwards for really
* large systems.
*/
static void adjust_jiffies_till_sched_qs(void)
{
unsigned long j;
/* If jiffies_till_sched_qs was specified, respect the request. */
if (jiffies_till_sched_qs != ULONG_MAX) {
WRITE_ONCE(jiffies_to_sched_qs, jiffies_till_sched_qs);
return;
}
/* Otherwise, set to third fqs scan, but bound below on large system. */
j = READ_ONCE(jiffies_till_first_fqs) +
2 * READ_ONCE(jiffies_till_next_fqs);
if (j < HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV)
j = HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
pr_info("RCU calculated value of scheduler-enlistment delay is %ld jiffies.\n", j);
WRITE_ONCE(jiffies_to_sched_qs, j);
}
static int param_set_first_fqs_jiffies(const char *val, const struct kernel_param *kp)
{
ulong j;
int ret = kstrtoul(val, 0, &j);
if (!ret) {
WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : j);
adjust_jiffies_till_sched_qs();
}
return ret;
}
static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param *kp)
{
ulong j;
int ret = kstrtoul(val, 0, &j);
if (!ret) {
WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : (j ?: 1));
adjust_jiffies_till_sched_qs();
}
return ret;
}
static const struct kernel_param_ops first_fqs_jiffies_ops = {
.set = param_set_first_fqs_jiffies,
.get = param_get_ulong,
};
static const struct kernel_param_ops next_fqs_jiffies_ops = {
.set = param_set_next_fqs_jiffies,
.get = param_get_ulong,
};
module_param_cb(jiffies_till_first_fqs, &first_fqs_jiffies_ops, &jiffies_till_first_fqs, 0644);
module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next_fqs, 0644);
module_param(rcu_kick_kthreads, bool, 0644);
static void force_qs_rnp(int (*f)(struct rcu_data *rdp));
static int rcu_pending(int user);
/*
* Return the number of RCU GPs completed thus far for debug & stats.
*/
unsigned long rcu_get_gp_seq(void)
{
return READ_ONCE(rcu_state.gp_seq);
}
EXPORT_SYMBOL_GPL(rcu_get_gp_seq);
/*
* Return the number of RCU expedited batches completed thus far for
* debug & stats. Odd numbers mean that a batch is in progress, even
* numbers mean idle. The value returned will thus be roughly double
* the cumulative batches since boot.
*/
unsigned long rcu_exp_batches_completed(void)
{
return rcu_state.expedited_sequence;
}
EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);
/*
* Return the root node of the rcu_state structure.
*/
static struct rcu_node *rcu_get_root(void)
{
return &rcu_state.node[0];
}
/*
* Send along grace-period-related data for rcutorture diagnostics.
*/
void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
unsigned long *gp_seq)
{
switch (test_type) {
case RCU_FLAVOR:
*flags = READ_ONCE(rcu_state.gp_flags);
*gp_seq = rcu_seq_current(&rcu_state.gp_seq);
break;
default:
break;
}
}
EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
#if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK))
/*
* An empty function that will trigger a reschedule on
* IRQ tail once IRQs get re-enabled on userspace/guest resume.
*/
static void late_wakeup_func(struct irq_work *work)
{
}
static DEFINE_PER_CPU(struct irq_work, late_wakeup_work) =
IRQ_WORK_INIT(late_wakeup_func);
/*
* If either:
*
* 1) the task is about to enter in guest mode and $ARCH doesn't support KVM generic work
* 2) the task is about to enter in user mode and $ARCH doesn't support generic entry.
*
* In these cases the late RCU wake ups aren't supported in the resched loops and our
* last resort is to fire a local irq_work that will trigger a reschedule once IRQs
* get re-enabled again.
*/
noinstr void rcu_irq_work_resched(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
if (IS_ENABLED(CONFIG_GENERIC_ENTRY) && !(current->flags & PF_VCPU))
return;
if (IS_ENABLED(CONFIG_KVM_XFER_TO_GUEST_WORK) && (current->flags & PF_VCPU))
return;
instrumentation_begin();
if (do_nocb_deferred_wakeup(rdp) && need_resched()) {
irq_work_queue(this_cpu_ptr(&late_wakeup_work));
}
instrumentation_end();
}
#endif /* #if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK)) */
#ifdef CONFIG_PROVE_RCU
/**
* rcu_irq_exit_check_preempt - Validate that scheduling is possible
*/
void rcu_irq_exit_check_preempt(void)
{
lockdep_assert_irqs_disabled();
RCU_LOCKDEP_WARN(ct_dynticks_nesting() <= 0,
"RCU dynticks_nesting counter underflow/zero!");
RCU_LOCKDEP_WARN(ct_dynticks_nmi_nesting() !=
DYNTICK_IRQ_NONIDLE,
"Bad RCU dynticks_nmi_nesting counter\n");
RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),
"RCU in extended quiescent state!");
}
#endif /* #ifdef CONFIG_PROVE_RCU */
#ifdef CONFIG_NO_HZ_FULL
/**
* __rcu_irq_enter_check_tick - Enable scheduler tick on CPU if RCU needs it.
*
* The scheduler tick is not normally enabled when CPUs enter the kernel
* from nohz_full userspace execution. After all, nohz_full userspace
* execution is an RCU quiescent state and the time executing in the kernel
* is quite short. Except of course when it isn't. And it is not hard to
* cause a large system to spend tens of seconds or even minutes looping
* in the kernel, which can cause a number of problems, include RCU CPU
* stall warnings.
*
* Therefore, if a nohz_full CPU fails to report a quiescent state
* in a timely manner, the RCU grace-period kthread sets that CPU's
* ->rcu_urgent_qs flag with the expectation that the next interrupt or
* exception will invoke this function, which will turn on the scheduler
* tick, which will enable RCU to detect that CPU's quiescent states,
* for example, due to cond_resched() calls in CONFIG_PREEMPT=n kernels.
* The tick will be disabled once a quiescent state is reported for
* this CPU.
*
* Of course, in carefully tuned systems, there might never be an
* interrupt or exception. In that case, the RCU grace-period kthread
* will eventually cause one to happen. However, in less carefully
* controlled environments, this function allows RCU to get what it
* needs without creating otherwise useless interruptions.
*/
void __rcu_irq_enter_check_tick(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
// If we're here from NMI there's nothing to do.
if (in_nmi())
return;
RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),
"Illegal rcu_irq_enter_check_tick() from extended quiescent state");
if (!tick_nohz_full_cpu(rdp->cpu) ||
!READ_ONCE(rdp->rcu_urgent_qs) ||
READ_ONCE(rdp->rcu_forced_tick)) {
// RCU doesn't need nohz_full help from this CPU, or it is
// already getting that help.
return;
}
// We get here only when not in an extended quiescent state and
// from interrupts (as opposed to NMIs). Therefore, (1) RCU is
// already watching and (2) The fact that we are in an interrupt
// handler and that the rcu_node lock is an irq-disabled lock
// prevents self-deadlock. So we can safely recheck under the lock.
// Note that the nohz_full state currently cannot change.
raw_spin_lock_rcu_node(rdp->mynode);
if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
// A nohz_full CPU is in the kernel and RCU needs a
// quiescent state. Turn on the tick!
WRITE_ONCE(rdp->rcu_forced_tick, true);
tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
}
raw_spin_unlock_rcu_node(rdp->mynode);
}
NOKPROBE_SYMBOL(__rcu_irq_enter_check_tick);
#endif /* CONFIG_NO_HZ_FULL */
/*
* Check to see if any future non-offloaded RCU-related work will need
* to be done by the current CPU, even if none need be done immediately,
* returning 1 if so. This function is part of the RCU implementation;
* it is -not- an exported member of the RCU API. This is used by
* the idle-entry code to figure out whether it is safe to disable the
* scheduler-clock interrupt.
*
* Just check whether or not this CPU has non-offloaded RCU callbacks
* queued.
*/
int rcu_needs_cpu(void)
{
return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) &&
!rcu_rdp_is_offloaded(this_cpu_ptr(&rcu_data));
}
/*
* If any sort of urgency was applied to the current CPU (for example,
* the scheduler-clock interrupt was enabled on a nohz_full CPU) in order
* to get to a quiescent state, disable it.
*/
static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp)
{
raw_lockdep_assert_held_rcu_node(rdp->mynode);
WRITE_ONCE(rdp->rcu_urgent_qs, false);
WRITE_ONCE(rdp->rcu_need_heavy_qs, false);
if (tick_nohz_full_cpu(rdp->cpu) && rdp->rcu_forced_tick) {
tick_dep_clear_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
WRITE_ONCE(rdp->rcu_forced_tick, false);
}
}
/**
* rcu_is_watching - see if RCU thinks that the current CPU is not idle
*
* Return true if RCU is watching the running CPU, which means that this
* CPU can safely enter RCU read-side critical sections. In other words,
* if the current CPU is not in its idle loop or is in an interrupt or
* NMI handler, return true.
*
* Make notrace because it can be called by the internal functions of
* ftrace, and making this notrace removes unnecessary recursion calls.
*/
notrace bool rcu_is_watching(void)
{
bool ret;
preempt_disable_notrace();
ret = !rcu_dynticks_curr_cpu_in_eqs();
preempt_enable_notrace();
return ret;
}
EXPORT_SYMBOL_GPL(rcu_is_watching);
/*
* If a holdout task is actually running, request an urgent quiescent
* state from its CPU. This is unsynchronized, so migrations can cause
* the request to go to the wrong CPU. Which is OK, all that will happen
* is that the CPU's next context switch will be a bit slower and next
* time around this task will generate another request.
*/
void rcu_request_urgent_qs_task(struct task_struct *t)
{
int cpu;
barrier();
cpu = task_cpu(t);
if (!task_curr(t))
return; /* This task is not running on that CPU. */
smp_store_release(per_cpu_ptr(&rcu_data.rcu_urgent_qs, cpu), true);
}
/*
* When trying to report a quiescent state on behalf of some other CPU,
* it is our responsibility to check for and handle potential overflow
* of the rcu_node ->gp_seq counter with respect to the rcu_data counters.
* After all, the CPU might be in deep idle state, and thus executing no
* code whatsoever.
*/
static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
{
raw_lockdep_assert_held_rcu_node(rnp);
if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + ULONG_MAX / 4,
rnp->gp_seq))
WRITE_ONCE(rdp->gpwrap, true);
if (ULONG_CMP_LT(rdp->rcu_iw_gp_seq + ULONG_MAX / 4, rnp->gp_seq))
rdp->rcu_iw_gp_seq = rnp->gp_seq + ULONG_MAX / 4;
}
/*
* Snapshot the specified CPU's dynticks counter so that we can later
* credit them with an implicit quiescent state. Return 1 if this CPU
* is in dynticks idle mode, which is an extended quiescent state.
*/
static int dyntick_save_progress_counter(struct rcu_data *rdp)
{
rdp->dynticks_snap = rcu_dynticks_snap(rdp->cpu);
if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
rcu_gpnum_ovf(rdp->mynode, rdp);
return 1;
}
return 0;
}
/*
* Return true if the specified CPU has passed through a quiescent
* state by virtue of being in or having passed through an dynticks
* idle state since the last call to dyntick_save_progress_counter()
* for this same CPU, or by virtue of having been offline.
*/
static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
{
unsigned long jtsq;
struct rcu_node *rnp = rdp->mynode;
/*
* If the CPU passed through or entered a dynticks idle phase with
* no active irq/NMI handlers, then we can safely pretend that the CPU
* already acknowledged the request to pass through a quiescent
* state. Either way, that CPU cannot possibly be in an RCU
* read-side critical section that started before the beginning
* of the current RCU grace period.
*/
if (rcu_dynticks_in_eqs_since(rdp, rdp->dynticks_snap)) {
trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
rcu_gpnum_ovf(rnp, rdp);
return 1;
}
/*
* Complain if a CPU that is considered to be offline from RCU's
* perspective has not yet reported a quiescent state. After all,
* the offline CPU should have reported a quiescent state during
* the CPU-offline process, or, failing that, by rcu_gp_init()
* if it ran concurrently with either the CPU going offline or the
* last task on a leaf rcu_node structure exiting its RCU read-side
* critical section while all CPUs corresponding to that structure
* are offline. This added warning detects bugs in any of these
* code paths.
*
* The rcu_node structure's ->lock is held here, which excludes
* the relevant portions the CPU-hotplug code, the grace-period
* initialization code, and the rcu_read_unlock() code paths.
*
* For more detail, please refer to the "Hotplug CPU" section
* of RCU's Requirements documentation.
*/
if (WARN_ON_ONCE(!rcu_rdp_cpu_online(rdp))) {
struct rcu_node *rnp1;
pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
__func__, rnp->grplo, rnp->grphi, rnp->level,
(long)rnp->gp_seq, (long)rnp->completedqs);
for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx ->rcu_gp_init_mask %#lx\n",
__func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext, rnp1->rcu_gp_init_mask);
pr_info("%s %d: %c online: %ld(%d) offline: %ld(%d)\n",
__func__, rdp->cpu, ".o"[rcu_rdp_cpu_online(rdp)],
(long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
(long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
return 1; /* Break things loose after complaining. */
}
/*
* A CPU running for an extended time within the kernel can
* delay RCU grace periods: (1) At age jiffies_to_sched_qs,
* set .rcu_urgent_qs, (2) At age 2*jiffies_to_sched_qs, set
* both .rcu_need_heavy_qs and .rcu_urgent_qs. Note that the
* unsynchronized assignments to the per-CPU rcu_need_heavy_qs
* variable are safe because the assignments are repeated if this
* CPU failed to pass through a quiescent state. This code
* also checks .jiffies_resched in case jiffies_to_sched_qs
* is set way high.
*/
jtsq = READ_ONCE(jiffies_to_sched_qs);
if (!READ_ONCE(rdp->rcu_need_heavy_qs) &&
(time_after(jiffies, rcu_state.gp_start + jtsq * 2) ||
time_after(jiffies, rcu_state.jiffies_resched) ||
rcu_state.cbovld)) {
WRITE_ONCE(rdp->rcu_need_heavy_qs, true);
/* Store rcu_need_heavy_qs before rcu_urgent_qs. */
smp_store_release(&rdp->rcu_urgent_qs, true);
} else if (time_after(jiffies, rcu_state.gp_start + jtsq)) {
WRITE_ONCE(rdp->rcu_urgent_qs, true);
}
/*
* NO_HZ_FULL CPUs can run in-kernel without rcu_sched_clock_irq!
* The above code handles this, but only for straight cond_resched().
* And some in-kernel loops check need_resched() before calling
* cond_resched(), which defeats the above code for CPUs that are
* running in-kernel with scheduling-clock interrupts disabled.
* So hit them over the head with the resched_cpu() hammer!
*/
if (tick_nohz_full_cpu(rdp->cpu) &&
(time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq * 3) ||
rcu_state.cbovld)) {
WRITE_ONCE(rdp->rcu_urgent_qs, true);
resched_cpu(rdp->cpu);
WRITE_ONCE(rdp->last_fqs_resched, jiffies);
}
/*
* If more than halfway to RCU CPU stall-warning time, invoke
* resched_cpu() more frequently to try to loosen things up a bit.
* Also check to see if the CPU is getting hammered with interrupts,
* but only once per grace period, just to keep the IPIs down to
* a dull roar.
*/
if (time_after(jiffies, rcu_state.jiffies_resched)) {
if (time_after(jiffies,
READ_ONCE(rdp->last_fqs_resched) + jtsq)) {
resched_cpu(rdp->cpu);
WRITE_ONCE(rdp->last_fqs_resched, jiffies);
}
if (IS_ENABLED(CONFIG_IRQ_WORK) &&
!rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
(rnp->ffmask & rdp->grpmask)) {
rdp->rcu_iw_pending = true;
rdp->rcu_iw_gp_seq = rnp->gp_seq;
irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
}
if (rcu_cpu_stall_cputime && rdp->snap_record.gp_seq != rdp->gp_seq) {
int cpu = rdp->cpu;
struct rcu_snap_record *rsrp;
struct kernel_cpustat *kcsp;
kcsp = &kcpustat_cpu(cpu);
rsrp = &rdp->snap_record;
rsrp->cputime_irq = kcpustat_field(kcsp, CPUTIME_IRQ, cpu);
rsrp->cputime_softirq = kcpustat_field(kcsp, CPUTIME_SOFTIRQ, cpu);
rsrp->cputime_system = kcpustat_field(kcsp, CPUTIME_SYSTEM, cpu);
rsrp->nr_hardirqs = kstat_cpu_irqs_sum(rdp->cpu);
rsrp->nr_softirqs = kstat_cpu_softirqs_sum(rdp->cpu);
rsrp->nr_csw = nr_context_switches_cpu(rdp->cpu);
rsrp->jiffies = jiffies;
rsrp->gp_seq = rdp->gp_seq;
}
}
return 0;
}
/* Trace-event wrapper function for trace_rcu_future_grace_period. */
static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
unsigned long gp_seq_req, const char *s)
{
trace_rcu_future_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
gp_seq_req, rnp->level,
rnp->grplo, rnp->grphi, s);
}
/*
* rcu_start_this_gp - Request the start of a particular grace period
* @rnp_start: The leaf node of the CPU from which to start.
* @rdp: The rcu_data corresponding to the CPU from which to start.
* @gp_seq_req: The gp_seq of the grace period to start.
*
* Start the specified grace period, as needed to handle newly arrived
* callbacks. The required future grace periods are recorded in each
* rcu_node structure's ->gp_seq_needed field. Returns true if there
* is reason to awaken the grace-period kthread.
*
* The caller must hold the specified rcu_node structure's ->lock, which
* is why the caller is responsible for waking the grace-period kthread.
*
* Returns true if the GP thread needs to be awakened else false.
*/
static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
unsigned long gp_seq_req)
{
bool ret = false;
struct rcu_node *rnp;
/*
* Use funnel locking to either acquire the root rcu_node
* structure's lock or bail out if the need for this grace period
* has already been recorded -- or if that grace period has in
* fact already started. If there is already a grace period in
* progress in a non-leaf node, no recording is needed because the
* end of the grace period will scan the leaf rcu_node structures.
* Note that rnp_start->lock must not be released.
*/
raw_lockdep_assert_held_rcu_node(rnp_start);
trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startleaf"));
for (rnp = rnp_start; 1; rnp = rnp->parent) {
if (rnp != rnp_start)
raw_spin_lock_rcu_node(rnp);
if (ULONG_CMP_GE(rnp->gp_seq_needed, gp_seq_req) ||
rcu_seq_started(&rnp->gp_seq, gp_seq_req) ||
(rnp != rnp_start &&
rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))) {
trace_rcu_this_gp(rnp, rdp, gp_seq_req,
TPS("Prestarted"));
goto unlock_out;
}
WRITE_ONCE(rnp->gp_seq_needed, gp_seq_req);
if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) {
/*
* We just marked the leaf or internal node, and a
* grace period is in progress, which means that
* rcu_gp_cleanup() will see the marking. Bail to
* reduce contention.
*/
trace_rcu_this_gp(rnp_start, rdp, gp_seq_req,
TPS("Startedleaf"));
goto unlock_out;
}
if (rnp != rnp_start && rnp->parent != NULL)
raw_spin_unlock_rcu_node(rnp);
if (!rnp->parent)
break; /* At root, and perhaps also leaf. */
}
/* If GP already in progress, just leave, otherwise start one. */
if (rcu_gp_in_progress()) {
trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedleafroot"));
goto unlock_out;
}
trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT);
WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
if (!READ_ONCE(rcu_state.gp_kthread)) {
trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
goto unlock_out;
}
trace_rcu_grace_period(rcu_state.name, data_race(rcu_state.gp_seq), TPS("newreq"));
ret = true; /* Caller must wake GP kthread. */
unlock_out:
/* Push furthest requested GP to leaf node and rcu_data structure. */
if (ULONG_CMP_LT(gp_seq_req, rnp->gp_seq_needed)) {
WRITE_ONCE(rnp_start->gp_seq_needed, rnp->gp_seq_needed);
WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
}
if (rnp != rnp_start)
raw_spin_unlock_rcu_node(rnp);
return ret;
}
/*
* Clean up any old requests for the just-ended grace period. Also return
* whether any additional grace periods have been requested.
*/
static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
{
bool needmore;
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
needmore = ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed);
if (!needmore)
rnp->gp_seq_needed = rnp->gp_seq; /* Avoid counter wrap. */
trace_rcu_this_gp(rnp, rdp, rnp->gp_seq,
needmore ? TPS("CleanupMore") : TPS("Cleanup"));
return needmore;
}
/*
* Awaken the grace-period kthread. Don't do a self-awaken (unless in an
* interrupt or softirq handler, in which case we just might immediately
* sleep upon return, resulting in a grace-period hang), and don't bother
* awakening when there is nothing for the grace-period kthread to do
* (as in several CPUs raced to awaken, we lost), and finally don't try
* to awaken a kthread that has not yet been created. If all those checks
* are passed, track some debug information and awaken.
*
* So why do the self-wakeup when in an interrupt or softirq handler
* in the grace-period kthread's context? Because the kthread might have
* been interrupted just as it was going to sleep, and just after the final
* pre-sleep check of the awaken condition. In this case, a wakeup really
* is required, and is therefore supplied.
*/
static void rcu_gp_kthread_wake(void)
{
struct task_struct *t = READ_ONCE(rcu_state.gp_kthread);
if ((current == t && !in_hardirq() && !in_serving_softirq()) ||
!READ_ONCE(rcu_state.gp_flags) || !t)
return;
WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
swake_up_one(&rcu_state.gp_wq);
}
/*
* If there is room, assign a ->gp_seq number to any callbacks on this
* CPU that have not already been assigned. Also accelerate any callbacks
* that were previously assigned a ->gp_seq number that has since proven
* to be too conservative, which can happen if callbacks get assigned a
* ->gp_seq number while RCU is idle, but with reference to a non-root
* rcu_node structure. This function is idempotent, so it does not hurt
* to call it repeatedly. Returns an flag saying that we should awaken
* the RCU grace-period kthread.
*
* The caller must hold rnp->lock with interrupts disabled.
*/
static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
{
unsigned long gp_seq_req;
bool ret = false;
rcu_lockdep_assert_cblist_protected(rdp);
raw_lockdep_assert_held_rcu_node(rnp);
/* If no pending (not yet ready to invoke) callbacks, nothing to do. */
if (!rcu_segcblist_pend_cbs(&rdp->cblist))
return false;
trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPreAcc"));
/*
* Callbacks are often registered with incomplete grace-period
* information. Something about the fact that getting exact
* information requires acquiring a global lock... RCU therefore
* makes a conservative estimate of the grace period number at which
* a given callback will become ready to invoke. The following
* code checks this estimate and improves it when possible, thus
* accelerating callback invocation to an earlier grace-period
* number.
*/
gp_seq_req = rcu_seq_snap(&rcu_state.gp_seq);
if (rcu_segcblist_accelerate(&rdp->cblist, gp_seq_req))
ret = rcu_start_this_gp(rnp, rdp, gp_seq_req);
/* Trace depending on how much we were able to accelerate. */
if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccWaitCB"));
else
trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccReadyCB"));
trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPostAcc"));
return ret;
}
/*
* Similar to rcu_accelerate_cbs(), but does not require that the leaf
* rcu_node structure's ->lock be held. It consults the cached value
* of ->gp_seq_needed in the rcu_data structure, and if that indicates
* that a new grace-period request be made, invokes rcu_accelerate_cbs()
* while holding the leaf rcu_node structure's ->lock.
*/
static void rcu_accelerate_cbs_unlocked(struct rcu_node *rnp,
struct rcu_data *rdp)
{
unsigned long c;
bool needwake;
rcu_lockdep_assert_cblist_protected(rdp);
c = rcu_seq_snap(&rcu_state.gp_seq);
if (!READ_ONCE(rdp->gpwrap) && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {
/* Old request still live, so mark recent callbacks. */
(void)rcu_segcblist_accelerate(&rdp->cblist, c);
return;
}
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
needwake = rcu_accelerate_cbs(rnp, rdp);
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
if (needwake)
rcu_gp_kthread_wake();
}
/*
* Move any callbacks whose grace period has completed to the
* RCU_DONE_TAIL sublist, then compact the remaining sublists and
* assign ->gp_seq numbers to any callbacks in the RCU_NEXT_TAIL
* sublist. This function is idempotent, so it does not hurt to
* invoke it repeatedly. As long as it is not invoked -too- often...
* Returns true if the RCU grace-period kthread needs to be awakened.
*
* The caller must hold rnp->lock with interrupts disabled.
*/
static bool rcu_advance_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
{
rcu_lockdep_assert_cblist_protected(rdp);
raw_lockdep_assert_held_rcu_node(rnp);
/* If no pending (not yet ready to invoke) callbacks, nothing to do. */
if (!rcu_segcblist_pend_cbs(&rdp->cblist))
return false;
/*
* Find all callbacks whose ->gp_seq numbers indicate that they
* are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
*/
rcu_segcblist_advance(&rdp->cblist, rnp->gp_seq);
/* Classify any remaining callbacks. */
return rcu_accelerate_cbs(rnp, rdp);
}
/*
* Move and classify callbacks, but only if doing so won't require
* that the RCU grace-period kthread be awakened.
*/
static void __maybe_unused rcu_advance_cbs_nowake(struct rcu_node *rnp,
struct rcu_data *rdp)
{
rcu_lockdep_assert_cblist_protected(rdp);
if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) || !raw_spin_trylock_rcu_node(rnp))
return;
// The grace period cannot end while we hold the rcu_node lock.
if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))
WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp));
raw_spin_unlock_rcu_node(rnp);
}
/*
* In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, attempt to generate a
* quiescent state. This is intended to be invoked when the CPU notices
* a new grace period.
*/
static void rcu_strict_gp_check_qs(void)
{
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
rcu_read_lock();
rcu_read_unlock();
}
}
/*
* Update CPU-local rcu_data state to record the beginnings and ends of
* grace periods. The caller must hold the ->lock of the leaf rcu_node
* structure corresponding to the current CPU, and must have irqs disabled.
* Returns true if the grace-period kthread needs to be awakened.
*/
static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp)
{
bool ret = false;
bool need_qs;
const bool offloaded = rcu_rdp_is_offloaded(rdp);
raw_lockdep_assert_held_rcu_node(rnp);
if (rdp->gp_seq == rnp->gp_seq)
return false; /* Nothing to do. */
/* Handle the ends of any preceding grace periods first. */
if (rcu_seq_completed_gp(rdp->gp_seq, rnp->gp_seq) ||
unlikely(READ_ONCE(rdp->gpwrap))) {
if (!offloaded)
ret = rcu_advance_cbs(rnp, rdp); /* Advance CBs. */
rdp->core_needs_qs = false;
trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuend"));
} else {
if (!offloaded)
ret = rcu_accelerate_cbs(rnp, rdp); /* Recent CBs. */
if (rdp->core_needs_qs)
rdp->core_needs_qs = !!(rnp->qsmask & rdp->grpmask);
}
/* Now handle the beginnings of any new-to-this-CPU grace periods. */
if (rcu_seq_new_gp(rdp->gp_seq, rnp->gp_seq) ||
unlikely(READ_ONCE(rdp->gpwrap))) {
/*
* If the current grace period is waiting for this CPU,
* set up to detect a quiescent state, otherwise don't
* go looking for one.
*/
trace_rcu_grace_period(rcu_state.name, rnp->gp_seq, TPS("cpustart"));
need_qs = !!(rnp->qsmask & rdp->grpmask);
rdp->cpu_no_qs.b.norm = need_qs;
rdp->core_needs_qs = need_qs;
zero_cpu_stall_ticks(rdp);
}
rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */
if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap)
WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
if (IS_ENABLED(CONFIG_PROVE_RCU) && READ_ONCE(rdp->gpwrap))
WRITE_ONCE(rdp->last_sched_clock, jiffies);
WRITE_ONCE(rdp->gpwrap, false);
rcu_gpnum_ovf(rnp, rdp);
return ret;
}
static void note_gp_changes(struct rcu_data *rdp)
{
unsigned long flags;
bool needwake;
struct rcu_node *rnp;
local_irq_save(flags);
rnp = rdp->mynode;
if ((rdp->gp_seq == rcu_seq_current(&rnp->gp_seq) &&
!unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
!raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
local_irq_restore(flags);
return;
}
needwake = __note_gp_changes(rnp, rdp);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
rcu_strict_gp_check_qs();
if (needwake)
rcu_gp_kthread_wake();
}
static atomic_t *rcu_gp_slow_suppress;
/* Register a counter to suppress debugging grace-period delays. */
void rcu_gp_slow_register(atomic_t *rgssp)
{
WARN_ON_ONCE(rcu_gp_slow_suppress);
WRITE_ONCE(rcu_gp_slow_suppress, rgssp);
}
EXPORT_SYMBOL_GPL(rcu_gp_slow_register);
/* Unregister a counter, with NULL for not caring which. */
void rcu_gp_slow_unregister(atomic_t *rgssp)
{
WARN_ON_ONCE(rgssp && rgssp != rcu_gp_slow_suppress);
WRITE_ONCE(rcu_gp_slow_suppress, NULL);
}
EXPORT_SYMBOL_GPL(rcu_gp_slow_unregister);
static bool rcu_gp_slow_is_suppressed(void)
{
atomic_t *rgssp = READ_ONCE(rcu_gp_slow_suppress);
return rgssp && atomic_read(rgssp);
}
static void rcu_gp_slow(int delay)
{
if (!rcu_gp_slow_is_suppressed() && delay > 0 &&
!(rcu_seq_ctr(rcu_state.gp_seq) % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
schedule_timeout_idle(delay);
}
static unsigned long sleep_duration;
/* Allow rcutorture to stall the grace-period kthread. */
void rcu_gp_set_torture_wait(int duration)
{
if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST) && duration > 0)
WRITE_ONCE(sleep_duration, duration);
}
EXPORT_SYMBOL_GPL(rcu_gp_set_torture_wait);
/* Actually implement the aforementioned wait. */
static void rcu_gp_torture_wait(void)
{
unsigned long duration;
if (!IS_ENABLED(CONFIG_RCU_TORTURE_TEST))
return;
duration = xchg(&sleep_duration, 0UL);
if (duration > 0) {
pr_alert("%s: Waiting %lu jiffies\n", __func__, duration);
schedule_timeout_idle(duration);
pr_alert("%s: Wait complete\n", __func__);
}
}
/*
* Handler for on_each_cpu() to invoke the target CPU's RCU core
* processing.
*/
static void rcu_strict_gp_boundary(void *unused)
{
invoke_rcu_core();
}
// Make the polled API aware of the beginning of a grace period.
static void rcu_poll_gp_seq_start(unsigned long *snap)
{
struct rcu_node *rnp = rcu_get_root();
if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
raw_lockdep_assert_held_rcu_node(rnp);
// If RCU was idle, note beginning of GP.
if (!rcu_seq_state(rcu_state.gp_seq_polled))
rcu_seq_start(&rcu_state.gp_seq_polled);
// Either way, record current state.
*snap = rcu_state.gp_seq_polled;
}
// Make the polled API aware of the end of a grace period.
static void rcu_poll_gp_seq_end(unsigned long *snap)
{
struct rcu_node *rnp = rcu_get_root();
if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
raw_lockdep_assert_held_rcu_node(rnp);
// If the previously noted GP is still in effect, record the
// end of that GP. Either way, zero counter to avoid counter-wrap
// problems.
if (*snap && *snap == rcu_state.gp_seq_polled) {
rcu_seq_end(&rcu_state.gp_seq_polled);
rcu_state.gp_seq_polled_snap = 0;
rcu_state.gp_seq_polled_exp_snap = 0;
} else {
*snap = 0;
}
}
// Make the polled API aware of the beginning of a grace period, but
// where caller does not hold the root rcu_node structure's lock.
static void rcu_poll_gp_seq_start_unlocked(unsigned long *snap)
{
unsigned long flags;
struct rcu_node *rnp = rcu_get_root();
if (rcu_init_invoked()) {
if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
lockdep_assert_irqs_enabled();
raw_spin_lock_irqsave_rcu_node(rnp, flags);
}
rcu_poll_gp_seq_start(snap);
if (rcu_init_invoked())
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
// Make the polled API aware of the end of a grace period, but where
// caller does not hold the root rcu_node structure's lock.
static void rcu_poll_gp_seq_end_unlocked(unsigned long *snap)
{
unsigned long flags;
struct rcu_node *rnp = rcu_get_root();
if (rcu_init_invoked()) {
if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
lockdep_assert_irqs_enabled();
raw_spin_lock_irqsave_rcu_node(rnp, flags);
}
rcu_poll_gp_seq_end(snap);
if (rcu_init_invoked())
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
/*
* Initialize a new grace period. Return false if no grace period required.
*/
static noinline_for_stack bool rcu_gp_init(void)
{
unsigned long flags;
unsigned long oldmask;
unsigned long mask;
struct rcu_data *rdp;
struct rcu_node *rnp = rcu_get_root();
WRITE_ONCE(rcu_state.gp_activity, jiffies);
raw_spin_lock_irq_rcu_node(rnp);
if (!READ_ONCE(rcu_state.gp_flags)) {
/* Spurious wakeup, tell caller to go back to sleep. */
raw_spin_unlock_irq_rcu_node(rnp);
return false;
}
WRITE_ONCE(rcu_state.gp_flags, 0); /* Clear all flags: New GP. */
if (WARN_ON_ONCE(rcu_gp_in_progress())) {
/*
* Grace period already in progress, don't start another.
* Not supposed to be able to happen.
*/
raw_spin_unlock_irq_rcu_node(rnp);
return false;
}
/* Advance to a new grace period and initialize state. */
record_gp_stall_check_time();
/* Record GP times before starting GP, hence rcu_seq_start(). */
rcu_seq_start(&rcu_state.gp_seq);
ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start"));
rcu_poll_gp_seq_start(&rcu_state.gp_seq_polled_snap);
raw_spin_unlock_irq_rcu_node(rnp);
/*
* Apply per-leaf buffered online and offline operations to
* the rcu_node tree. Note that this new grace period need not
* wait for subsequent online CPUs, and that RCU hooks in the CPU
* offlining path, when combined with checks in this function,
* will handle CPUs that are currently going offline or that will
* go offline later. Please also refer to "Hotplug CPU" section
* of RCU's Requirements documentation.
*/
WRITE_ONCE(rcu_state.gp_state, RCU_GP_ONOFF);
/* Exclude CPU hotplug operations. */
rcu_for_each_leaf_node(rnp) {
local_irq_save(flags);
arch_spin_lock(&rcu_state.ofl_lock);
raw_spin_lock_rcu_node(rnp);
if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
!rnp->wait_blkd_tasks) {
/* Nothing to do on this leaf rcu_node structure. */
raw_spin_unlock_rcu_node(rnp);
arch_spin_unlock(&rcu_state.ofl_lock);
local_irq_restore(flags);
continue;
}
/* Record old state, apply changes to ->qsmaskinit field. */
oldmask = rnp->qsmaskinit;
rnp->qsmaskinit = rnp->qsmaskinitnext;
/* If zero-ness of ->qsmaskinit changed, propagate up tree. */
if (!oldmask != !rnp->qsmaskinit) {
if (!oldmask) { /* First online CPU for rcu_node. */
if (!rnp->wait_blkd_tasks) /* Ever offline? */
rcu_init_new_rnp(rnp);
} else if (rcu_preempt_has_tasks(rnp)) {
rnp->wait_blkd_tasks = true; /* blocked tasks */
} else { /* Last offline CPU and can propagate. */
rcu_cleanup_dead_rnp(rnp);
}
}
/*
* If all waited-on tasks from prior grace period are
* done, and if all this rcu_node structure's CPUs are
* still offline, propagate up the rcu_node tree and
* clear ->wait_blkd_tasks. Otherwise, if one of this
* rcu_node structure's CPUs has since come back online,
* simply clear ->wait_blkd_tasks.
*/
if (rnp->wait_blkd_tasks &&
(!rcu_preempt_has_tasks(rnp) || rnp->qsmaskinit)) {
rnp->wait_blkd_tasks = false;
if (!rnp->qsmaskinit)
rcu_cleanup_dead_rnp(rnp);
}
raw_spin_unlock_rcu_node(rnp);
arch_spin_unlock(&rcu_state.ofl_lock);
local_irq_restore(flags);
}
rcu_gp_slow(gp_preinit_delay); /* Races with CPU hotplug. */
/*
* Set the quiescent-state-needed bits in all the rcu_node
* structures for all currently online CPUs in breadth-first
* order, starting from the root rcu_node structure, relying on the
* layout of the tree within the rcu_state.node[] array. Note that
* other CPUs will access only the leaves of the hierarchy, thus
* seeing that no grace period is in progress, at least until the
* corresponding leaf node has been initialized.
*
* The grace period cannot complete until the initialization
* process finishes, because this kthread handles both.
*/
WRITE_ONCE(rcu_state.gp_state, RCU_GP_INIT);
rcu_for_each_node_breadth_first(rnp) {
rcu_gp_slow(gp_init_delay);
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rdp = this_cpu_ptr(&rcu_data);
rcu_preempt_check_blocked_tasks(rnp);
rnp->qsmask = rnp->qsmaskinit;
WRITE_ONCE(rnp->gp_seq, rcu_state.gp_seq);
if (rnp == rdp->mynode)
(void)__note_gp_changes(rnp, rdp);
rcu_preempt_boost_start_gp(rnp);
trace_rcu_grace_period_init(rcu_state.name, rnp->gp_seq,
rnp->level, rnp->grplo,
rnp->grphi, rnp->qsmask);
/* Quiescent states for tasks on any now-offline CPUs. */
mask = rnp->qsmask & ~rnp->qsmaskinitnext;
rnp->rcu_gp_init_mask = mask;
if ((mask || rnp->wait_blkd_tasks) && rcu_is_leaf_node(rnp))
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
else
raw_spin_unlock_irq_rcu_node(rnp);
cond_resched_tasks_rcu_qs();
WRITE_ONCE(rcu_state.gp_activity, jiffies);
}
// If strict, make all CPUs aware of new grace period.
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
on_each_cpu(rcu_strict_gp_boundary, NULL, 0);
return true;
}
/*
* Helper function for swait_event_idle_exclusive() wakeup at force-quiescent-state
* time.
*/
static bool rcu_gp_fqs_check_wake(int *gfp)
{
struct rcu_node *rnp = rcu_get_root();
// If under overload conditions, force an immediate FQS scan.
if (*gfp & RCU_GP_FLAG_OVLD)
return true;
// Someone like call_rcu() requested a force-quiescent-state scan.
*gfp = READ_ONCE(rcu_state.gp_flags);
if (*gfp & RCU_GP_FLAG_FQS)
return true;
// The current grace period has completed.
if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
return true;
return false;
}
/*
* Do one round of quiescent-state forcing.
*/
static void rcu_gp_fqs(bool first_time)
{
struct rcu_node *rnp = rcu_get_root();
WRITE_ONCE(rcu_state.gp_activity, jiffies);
WRITE_ONCE(rcu_state.n_force_qs, rcu_state.n_force_qs + 1);
if (first_time) {
/* Collect dyntick-idle snapshots. */
force_qs_rnp(dyntick_save_progress_counter);
} else {
/* Handle dyntick-idle and offline CPUs. */
force_qs_rnp(rcu_implicit_dynticks_qs);
}
/* Clear flag to prevent immediate re-entry. */
if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
raw_spin_lock_irq_rcu_node(rnp);
WRITE_ONCE(rcu_state.gp_flags,
READ_ONCE(rcu_state.gp_flags) & ~RCU_GP_FLAG_FQS);
raw_spin_unlock_irq_rcu_node(rnp);
}
}
/*
* Loop doing repeated quiescent-state forcing until the grace period ends.
*/
static noinline_for_stack void rcu_gp_fqs_loop(void)
{
bool first_gp_fqs = true;
int gf = 0;
unsigned long j;
int ret;
struct rcu_node *rnp = rcu_get_root();
j = READ_ONCE(jiffies_till_first_fqs);
if (rcu_state.cbovld)
gf = RCU_GP_FLAG_OVLD;
ret = 0;
for (;;) {
if (rcu_state.cbovld) {
j = (j + 2) / 3;
if (j <= 0)
j = 1;
}
if (!ret || time_before(jiffies + j, rcu_state.jiffies_force_qs)) {
WRITE_ONCE(rcu_state.jiffies_force_qs, jiffies + j);
/*
* jiffies_force_qs before RCU_GP_WAIT_FQS state
* update; required for stall checks.
*/
smp_wmb();
WRITE_ONCE(rcu_state.jiffies_kick_kthreads,
jiffies + (j ? 3 * j : 2));
}
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
TPS("fqswait"));
WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_FQS);
(void)swait_event_idle_timeout_exclusive(rcu_state.gp_wq,
rcu_gp_fqs_check_wake(&gf), j);
rcu_gp_torture_wait();
WRITE_ONCE(rcu_state.gp_state, RCU_GP_DOING_FQS);
/* Locking provides needed memory barriers. */
/*
* Exit the loop if the root rcu_node structure indicates that the grace period
* has ended, leave the loop. The rcu_preempt_blocked_readers_cgp(rnp) check
* is required only for single-node rcu_node trees because readers blocking
* the current grace period are queued only on leaf rcu_node structures.
* For multi-node trees, checking the root node's ->qsmask suffices, because a
* given root node's ->qsmask bit is cleared only when all CPUs and tasks from
* the corresponding leaf nodes have passed through their quiescent state.
*/
if (!READ_ONCE(rnp->qsmask) &&
!rcu_preempt_blocked_readers_cgp(rnp))
break;
/* If time for quiescent-state forcing, do it. */
if (!time_after(rcu_state.jiffies_force_qs, jiffies) ||
(gf & (RCU_GP_FLAG_FQS | RCU_GP_FLAG_OVLD))) {
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
TPS("fqsstart"));
rcu_gp_fqs(first_gp_fqs);
gf = 0;
if (first_gp_fqs) {
first_gp_fqs = false;
gf = rcu_state.cbovld ? RCU_GP_FLAG_OVLD : 0;
}
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
TPS("fqsend"));
cond_resched_tasks_rcu_qs();
WRITE_ONCE(rcu_state.gp_activity, jiffies);
ret = 0; /* Force full wait till next FQS. */
j = READ_ONCE(jiffies_till_next_fqs);
} else {
/* Deal with stray signal. */
cond_resched_tasks_rcu_qs();
WRITE_ONCE(rcu_state.gp_activity, jiffies);
WARN_ON(signal_pending(current));
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
TPS("fqswaitsig"));
ret = 1; /* Keep old FQS timing. */
j = jiffies;
if (time_after(jiffies, rcu_state.jiffies_force_qs))
j = 1;
else
j = rcu_state.jiffies_force_qs - j;
gf = 0;
}
}
}
/*
* Clean up after the old grace period.
*/
static noinline void rcu_gp_cleanup(void)
{
int cpu;
bool needgp = false;
unsigned long gp_duration;
unsigned long new_gp_seq;
bool offloaded;
struct rcu_data *rdp;
struct rcu_node *rnp = rcu_get_root();
struct swait_queue_head *sq;
WRITE_ONCE(rcu_state.gp_activity, jiffies);
raw_spin_lock_irq_rcu_node(rnp);
rcu_state.gp_end = jiffies;
gp_duration = rcu_state.gp_end - rcu_state.gp_start;
if (gp_duration > rcu_state.gp_max)
rcu_state.gp_max = gp_duration;
/*
* We know the grace period is complete, but to everyone else
* it appears to still be ongoing. But it is also the case
* that to everyone else it looks like there is nothing that
* they can do to advance the grace period. It is therefore
* safe for us to drop the lock in order to mark the grace
* period as completed in all of the rcu_node structures.
*/
rcu_poll_gp_seq_end(&rcu_state.gp_seq_polled_snap);
raw_spin_unlock_irq_rcu_node(rnp);
/*
* Propagate new ->gp_seq value to rcu_node structures so that
* other CPUs don't have to wait until the start of the next grace
* period to process their callbacks. This also avoids some nasty
* RCU grace-period initialization races by forcing the end of
* the current grace period to be completely recorded in all of
* the rcu_node structures before the beginning of the next grace
* period is recorded in any of the rcu_node structures.
*/
new_gp_seq = rcu_state.gp_seq;
rcu_seq_end(&new_gp_seq);
rcu_for_each_node_breadth_first(rnp) {
raw_spin_lock_irq_rcu_node(rnp);
if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
dump_blkd_tasks(rnp, 10);
WARN_ON_ONCE(rnp->qsmask);
WRITE_ONCE(rnp->gp_seq, new_gp_seq);
if (!rnp->parent)
smp_mb(); // Order against failing poll_state_synchronize_rcu_full().
rdp = this_cpu_ptr(&rcu_data);
if (rnp == rdp->mynode)
needgp = __note_gp_changes(rnp, rdp) || needgp;
/* smp_mb() provided by prior unlock-lock pair. */
needgp = rcu_future_gp_cleanup(rnp) || needgp;
// Reset overload indication for CPUs no longer overloaded
if (rcu_is_leaf_node(rnp))
for_each_leaf_node_cpu_mask(rnp, cpu, rnp->cbovldmask) {
rdp = per_cpu_ptr(&rcu_data, cpu);
check_cb_ovld_locked(rdp, rnp);
}
sq = rcu_nocb_gp_get(rnp);
raw_spin_unlock_irq_rcu_node(rnp);
rcu_nocb_gp_cleanup(sq);
cond_resched_tasks_rcu_qs();
WRITE_ONCE(rcu_state.gp_activity, jiffies);
rcu_gp_slow(gp_cleanup_delay);
}
rnp = rcu_get_root();
raw_spin_lock_irq_rcu_node(rnp); /* GP before ->gp_seq update. */
/* Declare grace period done, trace first to use old GP number. */
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end"));
rcu_seq_end(&rcu_state.gp_seq);
ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
WRITE_ONCE(rcu_state.gp_state, RCU_GP_IDLE);
/* Check for GP requests since above loop. */
rdp = this_cpu_ptr(&rcu_data);
if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) {
trace_rcu_this_gp(rnp, rdp, rnp->gp_seq_needed,
TPS("CleanupMore"));
needgp = true;
}
/* Advance CBs to reduce false positives below. */
offloaded = rcu_rdp_is_offloaded(rdp);
if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) {
// We get here if a grace period was needed (“needgp”)
// and the above call to rcu_accelerate_cbs() did not set
// the RCU_GP_FLAG_INIT bit in ->gp_state (which records
// the need for another grace period).  The purpose
// of the “offloaded” check is to avoid invoking
// rcu_accelerate_cbs() on an offloaded CPU because we do not
// hold the ->nocb_lock needed to safely access an offloaded
// ->cblist.  We do not want to acquire that lock because
// it can be heavily contended during callback floods.
WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT);
WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("newreq"));
} else {
// We get here either if there is no need for an
// additional grace period or if rcu_accelerate_cbs() has
// already set the RCU_GP_FLAG_INIT bit in ->gp_flags. 
// So all we need to do is to clear all of the other
// ->gp_flags bits.
WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags & RCU_GP_FLAG_INIT);
}
raw_spin_unlock_irq_rcu_node(rnp);
// If strict, make all CPUs aware of the end of the old grace period.
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
on_each_cpu(rcu_strict_gp_boundary, NULL, 0);
}
/*
* Body of kthread that handles grace periods.
*/
static int __noreturn rcu_gp_kthread(void *unused)
{
rcu_bind_gp_kthread();
for (;;) {
/* Handle grace-period start. */
for (;;) {
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
TPS("reqwait"));
WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_GPS);
swait_event_idle_exclusive(rcu_state.gp_wq,
READ_ONCE(rcu_state.gp_flags) &
RCU_GP_FLAG_INIT);
rcu_gp_torture_wait();
WRITE_ONCE(rcu_state.gp_state, RCU_GP_DONE_GPS);
/* Locking provides needed memory barrier. */
if (rcu_gp_init())
break;
cond_resched_tasks_rcu_qs();
WRITE_ONCE(rcu_state.gp_activity, jiffies);
WARN_ON(signal_pending(current));
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
TPS("reqwaitsig"));
}
/* Handle quiescent-state forcing. */
rcu_gp_fqs_loop();
/* Handle grace-period end. */
WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANUP);
rcu_gp_cleanup();
WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANED);
}
}
/*
* Report a full set of quiescent states to the rcu_state data structure.
* Invoke rcu_gp_kthread_wake() to awaken the grace-period kthread if
* another grace period is required. Whether we wake the grace-period
* kthread or it awakens itself for the next round of quiescent-state
* forcing, that kthread will clean up after the just-completed grace
* period. Note that the caller must hold rnp->lock, which is released
* before return.
*/
static void rcu_report_qs_rsp(unsigned long flags)
__releases(rcu_get_root()->lock)
{
raw_lockdep_assert_held_rcu_node(rcu_get_root());
WARN_ON_ONCE(!rcu_gp_in_progress());
WRITE_ONCE(rcu_state.gp_flags,
READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(), flags);
rcu_gp_kthread_wake();
}
/*
* Similar to rcu_report_qs_rdp(), for which it is a helper function.
* Allows quiescent states for a group of CPUs to be reported at one go
* to the specified rcu_node structure, though all the CPUs in the group
* must be represented by the same rcu_node structure (which need not be a
* leaf rcu_node structure, though it often will be). The gps parameter
* is the grace-period snapshot, which means that the quiescent states
* are valid only if rnp->gp_seq is equal to gps. That structure's lock
* must be held upon entry, and it is released before return.
*
* As a special case, if mask is zero, the bit-already-cleared check is
* disabled. This allows propagating quiescent state due to resumed tasks
* during grace-period initialization.
*/
static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
unsigned long gps, unsigned long flags)
__releases(rnp->lock)
{
unsigned long oldmask = 0;
struct rcu_node *rnp_c;
raw_lockdep_assert_held_rcu_node(rnp);
/* Walk up the rcu_node hierarchy. */
for (;;) {
if ((!(rnp->qsmask & mask) && mask) || rnp->gp_seq != gps) {
/*
* Our bit has already been cleared, or the
* relevant grace period is already over, so done.
*/
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
WARN_ON_ONCE(!rcu_is_leaf_node(rnp) &&
rcu_preempt_blocked_readers_cgp(rnp));
WRITE_ONCE(rnp->qsmask, rnp->qsmask & ~mask);
trace_rcu_quiescent_state_report(rcu_state.name, rnp->gp_seq,
mask, rnp->qsmask, rnp->level,
rnp->grplo, rnp->grphi,
!!rnp->gp_tasks);
if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
/* Other bits still set at this level, so done. */
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
rnp->completedqs = rnp->gp_seq;
mask = rnp->grpmask;
if (rnp->parent == NULL) {
/* No more levels. Exit loop holding root lock. */
break;
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
rnp_c = rnp;
rnp = rnp->parent;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
oldmask = READ_ONCE(rnp_c->qsmask);
}
/*
* Get here if we are the last CPU to pass through a quiescent
* state for this grace period. Invoke rcu_report_qs_rsp()
* to clean up and start the next grace period if one is needed.
*/
rcu_report_qs_rsp(flags); /* releases rnp->lock. */
}
/*
* Record a quiescent state for all tasks that were previously queued
* on the specified rcu_node structure and that were blocking the current
* RCU grace period. The caller must hold the corresponding rnp->lock with
* irqs disabled, and this lock is released upon return, but irqs remain
* disabled.
*/
static void __maybe_unused
rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
__releases(rnp->lock)
{
unsigned long gps;
unsigned long mask;
struct rcu_node *rnp_p;
raw_lockdep_assert_held_rcu_node(rnp);
if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT_RCU)) ||
WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)) ||
rnp->qsmask != 0) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return; /* Still need more quiescent states! */
}
rnp->completedqs = rnp->gp_seq;
rnp_p = rnp->parent;
if (rnp_p == NULL) {
/*
* Only one rcu_node structure in the tree, so don't
* try to report up to its nonexistent parent!
*/
rcu_report_qs_rsp(flags);
return;
}
/* Report up the rest of the hierarchy, tracking current ->gp_seq. */
gps = rnp->gp_seq;
mask = rnp->grpmask;
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */
rcu_report_qs_rnp(mask, rnp_p, gps, flags);
}
/*
* Record a quiescent state for the specified CPU to that CPU's rcu_data
* structure. This must be called from the specified CPU.
*/
static void
rcu_report_qs_rdp(struct rcu_data *rdp)
{
unsigned long flags;
unsigned long mask;
bool needwake = false;
bool needacc = false;
struct rcu_node *rnp;
WARN_ON_ONCE(rdp->cpu != smp_processor_id());
rnp = rdp->mynode;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (rdp->cpu_no_qs.b.norm || rdp->gp_seq != rnp->gp_seq ||
rdp->gpwrap) {
/*
* The grace period in which this quiescent state was
* recorded has ended, so don't report it upwards.
* We will instead need a new quiescent state that lies
* within the current grace period.
*/
rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
mask = rdp->grpmask;
rdp->core_needs_qs = false;
if ((rnp->qsmask & mask) == 0) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
} else {
/*
* This GP can't end until cpu checks in, so all of our
* callbacks can be processed during the next GP.
*
* NOCB kthreads have their own way to deal with that...
*/
if (!rcu_rdp_is_offloaded(rdp)) {
needwake = rcu_accelerate_cbs(rnp, rdp);
} else if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) {
/*
* ...but NOCB kthreads may miss or delay callbacks acceleration
* if in the middle of a (de-)offloading process.
*/
needacc = true;
}
rcu_disable_urgency_upon_qs(rdp);
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
/* ^^^ Released rnp->lock */
if (needwake)
rcu_gp_kthread_wake();
if (needacc) {
rcu_nocb_lock_irqsave(rdp, flags);
rcu_accelerate_cbs_unlocked(rnp, rdp);
rcu_nocb_unlock_irqrestore(rdp, flags);
}
}
}
/*
* Check to see if there is a new grace period of which this CPU
* is not yet aware, and if so, set up local rcu_data state for it.
* Otherwise, see if this CPU has just passed through its first
* quiescent state for this grace period, and record that fact if so.
*/
static void
rcu_check_quiescent_state(struct rcu_data *rdp)
{
/* Check for grace-period ends and beginnings. */
note_gp_changes(rdp);
/*
* Does this CPU still need to do its part for current grace period?
* If no, return and let the other CPUs do their part as well.
*/
if (!rdp->core_needs_qs)
return;
/*
* Was there a quiescent state since the beginning of the grace
* period? If no, then exit and wait for the next call.
*/
if (rdp->cpu_no_qs.b.norm)
return;
/*
* Tell RCU we are done (but rcu_report_qs_rdp() will be the
* judge of that).
*/
rcu_report_qs_rdp(rdp);
}
/*
* Invoke any RCU callbacks that have made it to the end of their grace
* period. Throttle as specified by rdp->blimit.
*/
static void rcu_do_batch(struct rcu_data *rdp)
{
int div;
bool __maybe_unused empty;
unsigned long flags;
struct rcu_head *rhp;
struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
long bl, count = 0;
long pending, tlimit = 0;
/* If no callbacks are ready, just return. */
if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
trace_rcu_batch_start(rcu_state.name,
rcu_segcblist_n_cbs(&rdp->cblist), 0);
trace_rcu_batch_end(rcu_state.name, 0,
!rcu_segcblist_empty(&rdp->cblist),
need_resched(), is_idle_task(current),
rcu_is_callbacks_kthread(rdp));
return;
}
/*
* Extract the list of ready callbacks, disabling IRQs to prevent
* races with call_rcu() from interrupt handlers. Leave the
* callback counts, as rcu_barrier() needs to be conservative.
*/
rcu_nocb_lock_irqsave(rdp, flags);
WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
pending = rcu_segcblist_get_seglen(&rdp->cblist, RCU_DONE_TAIL);
div = READ_ONCE(rcu_divisor);
div = div < 0 ? 7 : div > sizeof(long) * 8 - 2 ? sizeof(long) * 8 - 2 : div;
bl = max(rdp->blimit, pending >> div);
if (in_serving_softirq() && unlikely(bl > 100)) {
long rrn = READ_ONCE(rcu_resched_ns);
rrn = rrn < NSEC_PER_MSEC ? NSEC_PER_MSEC : rrn > NSEC_PER_SEC ? NSEC_PER_SEC : rrn;
tlimit = local_clock() + rrn;
}
trace_rcu_batch_start(rcu_state.name,
rcu_segcblist_n_cbs(&rdp->cblist), bl);
rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
if (rcu_rdp_is_offloaded(rdp))
rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbDequeued"));
rcu_nocb_unlock_irqrestore(rdp, flags);
/* Invoke callbacks. */
tick_dep_set_task(current, TICK_DEP_BIT_RCU);
rhp = rcu_cblist_dequeue(&rcl);
for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
rcu_callback_t f;
count++;
debug_rcu_head_unqueue(rhp);
rcu_lock_acquire(&rcu_callback_map);
trace_rcu_invoke_callback(rcu_state.name, rhp);
f = rhp->func;
WRITE_ONCE(rhp->func, (rcu_callback_t)0L);
f(rhp);
rcu_lock_release(&rcu_callback_map);
/*
* Stop only if limit reached and CPU has something to do.
*/
if (in_serving_softirq()) {
if (count >= bl && (need_resched() || !is_idle_task(current)))
break;
/*
* Make sure we don't spend too much time here and deprive other
* softirq vectors of CPU cycles.
*/
if (unlikely(tlimit)) {
/* only call local_clock() every 32 callbacks */
if (likely((count & 31) || local_clock() < tlimit))
continue;
/* Exceeded the time limit, so leave. */
break;
}
} else {
local_bh_enable();
lockdep_assert_irqs_enabled();
cond_resched_tasks_rcu_qs();
lockdep_assert_irqs_enabled();
local_bh_disable();
}
}
rcu_nocb_lock_irqsave(rdp, flags);
rdp->n_cbs_invoked += count;
trace_rcu_batch_end(rcu_state.name, count, !!rcl.head, need_resched(),
is_idle_task(current), rcu_is_callbacks_kthread(rdp));
/* Update counts and requeue any remaining callbacks. */
rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
rcu_segcblist_add_len(&rdp->cblist, -count);
/* Reinstate batch limit if we have worked down the excess. */
count = rcu_segcblist_n_cbs(&rdp->cblist);
if (rdp->blimit >= DEFAULT_MAX_RCU_BLIMIT && count <= qlowmark)
rdp->blimit = blimit;
/* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
if (count == 0 && rdp->qlen_last_fqs_check != 0) {
rdp->qlen_last_fqs_check = 0;
rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
} else if (count < rdp->qlen_last_fqs_check - qhimark)
rdp->qlen_last_fqs_check = count;
/*
* The following usually indicates a double call_rcu(). To track
* this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y.
*/
empty = rcu_segcblist_empty(&rdp->cblist);
WARN_ON_ONCE(count == 0 && !empty);
WARN_ON_ONCE(!IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
count != 0 && empty);
WARN_ON_ONCE(count == 0 && rcu_segcblist_n_segment_cbs(&rdp->cblist) != 0);
WARN_ON_ONCE(!empty && rcu_segcblist_n_segment_cbs(&rdp->cblist) == 0);
rcu_nocb_unlock_irqrestore(rdp, flags);
tick_dep_clear_task(current, TICK_DEP_BIT_RCU);
}
/*
* This function is invoked from each scheduling-clock interrupt,
* and checks to see if this CPU is in a non-context-switch quiescent
* state, for example, user mode or idle loop. It also schedules RCU
* core processing. If the current grace period has gone on too long,
* it will ask the scheduler to manufacture a context switch for the sole
* purpose of providing the needed quiescent state.
*/
void rcu_sched_clock_irq(int user)
{
unsigned long j;
if (IS_ENABLED(CONFIG_PROVE_RCU)) {
j = jiffies;
WARN_ON_ONCE(time_before(j, __this_cpu_read(rcu_data.last_sched_clock)));
__this_cpu_write(rcu_data.last_sched_clock, j);
}
trace_rcu_utilization(TPS("Start scheduler-tick"));
lockdep_assert_irqs_disabled();
raw_cpu_inc(rcu_data.ticks_this_gp);
/* The load-acquire pairs with the store-release setting to true. */
if (smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
/* Idle and userspace execution already are quiescent states. */
if (!rcu_is_cpu_rrupt_from_idle() && !user) {
set_tsk_need_resched(current);
set_preempt_need_resched();
}
__this_cpu_write(rcu_data.rcu_urgent_qs, false);
}
rcu_flavor_sched_clock_irq(user);
if (rcu_pending(user))
invoke_rcu_core();
if (user || rcu_is_cpu_rrupt_from_idle())
rcu_note_voluntary_context_switch(current);
lockdep_assert_irqs_disabled();
trace_rcu_utilization(TPS("End scheduler-tick"));
}
/*
* Scan the leaf rcu_node structures. For each structure on which all
* CPUs have reported a quiescent state and on which there are tasks
* blocking the current grace period, initiate RCU priority boosting.
* Otherwise, invoke the specified function to check dyntick state for
* each CPU that has not yet reported a quiescent state.
*/
static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
{
int cpu;
unsigned long flags;
unsigned long mask;
struct rcu_data *rdp;
struct rcu_node *rnp;
rcu_state.cbovld = rcu_state.cbovldnext;
rcu_state.cbovldnext = false;
rcu_for_each_leaf_node(rnp) {
cond_resched_tasks_rcu_qs();
mask = 0;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rcu_state.cbovldnext |= !!rnp->cbovldmask;
if (rnp->qsmask == 0) {
if (rcu_preempt_blocked_readers_cgp(rnp)) {
/*
* No point in scanning bits because they
* are all zero. But we might need to
* priority-boost blocked readers.
*/
rcu_initiate_boost(rnp, flags);
/* rcu_initiate_boost() releases rnp->lock */
continue;
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
continue;
}
for_each_leaf_node_cpu_mask(rnp, cpu, rnp->qsmask) {
rdp = per_cpu_ptr(&rcu_data, cpu);
if (f(rdp)) {
mask |= rdp->grpmask;
rcu_disable_urgency_upon_qs(rdp);
}
}
if (mask != 0) {
/* Idle/offline CPUs, report (releases rnp->lock). */
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
} else {
/* Nothing to do here, so just drop the lock. */
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
}
}
/*
* Force quiescent states on reluctant CPUs, and also detect which
* CPUs are in dyntick-idle mode.
*/
void rcu_force_quiescent_state(void)
{
unsigned long flags;
bool ret;
struct rcu_node *rnp;
struct rcu_node *rnp_old = NULL;
/* Funnel through hierarchy to reduce memory contention. */
rnp = raw_cpu_read(rcu_data.mynode);
for (; rnp != NULL; rnp = rnp->parent) {
ret = (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) ||
!raw_spin_trylock(&rnp->fqslock);
if (rnp_old != NULL)
raw_spin_unlock(&rnp_old->fqslock);
if (ret)
return;
rnp_old = rnp;
}
/* rnp_old == rcu_get_root(), rnp == NULL. */
/* Reached the root of the rcu_node tree, acquire lock. */
raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
raw_spin_unlock(&rnp_old->fqslock);
if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
return; /* Someone beat us to it. */
}
WRITE_ONCE(rcu_state.gp_flags,
READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
rcu_gp_kthread_wake();
}
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
// Workqueue handler for an RCU reader for kernels enforcing struct RCU
// grace periods.
static void strict_work_handler(struct work_struct *work)
{
rcu_read_lock();
rcu_read_unlock();
}
/* Perform RCU core processing work for the current CPU. */
static __latent_entropy void rcu_core(void)
{
unsigned long flags;
struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
struct rcu_node *rnp = rdp->mynode;
/*
* On RT rcu_core() can be preempted when IRQs aren't disabled.
* Therefore this function can race with concurrent NOCB (de-)offloading
* on this CPU and the below condition must be considered volatile.
* However if we race with:
*
* _ Offloading: In the worst case we accelerate or process callbacks
* concurrently with NOCB kthreads. We are guaranteed to
* call rcu_nocb_lock() if that happens.
*
* _ Deoffloading: In the worst case we miss callbacks acceleration or
* processing. This is fine because the early stage
* of deoffloading invokes rcu_core() after setting
* SEGCBLIST_RCU_CORE. So we guarantee that we'll process
* what could have been dismissed without the need to wait
* for the next rcu_pending() check in the next jiffy.
*/
const bool do_batch = !rcu_segcblist_completely_offloaded(&rdp->cblist);
if (cpu_is_offline(smp_processor_id()))
return;
trace_rcu_utilization(TPS("Start RCU core"));
WARN_ON_ONCE(!rdp->beenonline);
/* Report any deferred quiescent states if preemption enabled. */
if (IS_ENABLED(CONFIG_PREEMPT_COUNT) && (!(preempt_count() & PREEMPT_MASK))) {
rcu_preempt_deferred_qs(current);
} else if (rcu_preempt_need_deferred_qs(current)) {
set_tsk_need_resched(current);
set_preempt_need_resched();
}
/* Update RCU state based on any recent quiescent states. */
rcu_check_quiescent_state(rdp);
/* No grace period and unregistered callbacks? */
if (!rcu_gp_in_progress() &&
rcu_segcblist_is_enabled(&rdp->cblist) && do_batch) {
rcu_nocb_lock_irqsave(rdp, flags);
if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
rcu_accelerate_cbs_unlocked(rnp, rdp);
rcu_nocb_unlock_irqrestore(rdp, flags);
}
rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check());
/* If there are callbacks ready, invoke them. */
if (do_batch && rcu_segcblist_ready_cbs(&rdp->cblist) &&
likely(READ_ONCE(rcu_scheduler_fully_active))) {
rcu_do_batch(rdp);
/* Re-invoke RCU core processing if there are callbacks remaining. */
if (rcu_segcblist_ready_cbs(&rdp->cblist))
invoke_rcu_core();
}
/* Do any needed deferred wakeups of rcuo kthreads. */
do_nocb_deferred_wakeup(rdp);
trace_rcu_utilization(TPS("End RCU core"));
// If strict GPs, schedule an RCU reader in a clean environment.
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
queue_work_on(rdp->cpu, rcu_gp_wq, &rdp->strict_work);
}
static void rcu_core_si(struct softirq_action *h)
{
rcu_core();
}
static void rcu_wake_cond(struct task_struct *t, int status)
{
/*
* If the thread is yielding, only wake it when this
* is invoked from idle
*/
if (t && (status != RCU_KTHREAD_YIELDING || is_idle_task(current)))
wake_up_process(t);
}
static void invoke_rcu_core_kthread(void)
{
struct task_struct *t;
unsigned long flags;
local_irq_save(flags);
__this_cpu_write(rcu_data.rcu_cpu_has_work, 1);
t = __this_cpu_read(rcu_data.rcu_cpu_kthread_task);
if (t != NULL && t != current)
rcu_wake_cond(t, __this_cpu_read(rcu_data.rcu_cpu_kthread_status));
local_irq_restore(flags);
}
/*
* Wake up this CPU's rcuc kthread to do RCU core processing.
*/
static void invoke_rcu_core(void)
{
if (!cpu_online(smp_processor_id()))
return;
if (use_softirq)
raise_softirq(RCU_SOFTIRQ);
else
invoke_rcu_core_kthread();
}
static void rcu_cpu_kthread_park(unsigned int cpu)
{
per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
}
static int rcu_cpu_kthread_should_run(unsigned int cpu)
{
return __this_cpu_read(rcu_data.rcu_cpu_has_work);
}
/*
* Per-CPU kernel thread that invokes RCU callbacks. This replaces
* the RCU softirq used in configurations of RCU that do not support RCU
* priority boosting.
*/
static void rcu_cpu_kthread(unsigned int cpu)
{
unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status);
char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work);
unsigned long *j = this_cpu_ptr(&rcu_data.rcuc_activity);
int spincnt;
trace_rcu_utilization(TPS("Start CPU kthread@rcu_run"));
for (spincnt = 0; spincnt < 10; spincnt++) {
WRITE_ONCE(*j, jiffies);
local_bh_disable();
*statusp = RCU_KTHREAD_RUNNING;
local_irq_disable();
work = *workp;
*workp = 0;
local_irq_enable();
if (work)
rcu_core();
local_bh_enable();
if (*workp == 0) {
trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
*statusp = RCU_KTHREAD_WAITING;
return;
}
}
*statusp = RCU_KTHREAD_YIELDING;
trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
schedule_timeout_idle(2);
trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
*statusp = RCU_KTHREAD_WAITING;
WRITE_ONCE(*j, jiffies);
}
static struct smp_hotplug_thread rcu_cpu_thread_spec = {
.store = &rcu_data.rcu_cpu_kthread_task,
.thread_should_run = rcu_cpu_kthread_should_run,
.thread_fn = rcu_cpu_kthread,
.thread_comm = "rcuc/%u",
.setup = rcu_cpu_kthread_setup,
.park = rcu_cpu_kthread_park,
};
/*
* Spawn per-CPU RCU core processing kthreads.
*/
static int __init rcu_spawn_core_kthreads(void)
{
int cpu;
for_each_possible_cpu(cpu)
per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0;
if (use_softirq)
return 0;
WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec),
"%s: Could not start rcuc kthread, OOM is now expected behavior\n", __func__);
return 0;
}
/*
* Handle any core-RCU processing required by a call_rcu() invocation.
*/
static void __call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
unsigned long flags)
{
/*
* If called from an extended quiescent state, invoke the RCU
* core in order to force a re-evaluation of RCU's idleness.
*/
if (!rcu_is_watching())
invoke_rcu_core();
/* If interrupts were disabled or CPU offline, don't invoke RCU core. */
if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
return;
/*
* Force the grace period if too many callbacks or too long waiting.
* Enforce hysteresis, and don't invoke rcu_force_quiescent_state()
* if some other CPU has recently done so. Also, don't bother
* invoking rcu_force_quiescent_state() if the newly enqueued callback
* is the only one waiting for a grace period to complete.
*/
if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
rdp->qlen_last_fqs_check + qhimark)) {
/* Are we ignoring a completed grace period? */
note_gp_changes(rdp);
/* Start a new grace period if one not already started. */
if (!rcu_gp_in_progress()) {
rcu_accelerate_cbs_unlocked(rdp->mynode, rdp);
} else {
/* Give the grace period a kick. */
rdp->blimit = DEFAULT_MAX_RCU_BLIMIT;
if (READ_ONCE(rcu_state.n_force_qs) == rdp->n_force_qs_snap &&
rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
rcu_force_quiescent_state();
rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
}
}
}
/*
* RCU callback function to leak a callback.
*/
static void rcu_leak_callback(struct rcu_head *rhp)
{
}
/*
* Check and if necessary update the leaf rcu_node structure's
* ->cbovldmask bit corresponding to the current CPU based on that CPU's
* number of queued RCU callbacks. The caller must hold the leaf rcu_node
* structure's ->lock.
*/
static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp)
{
raw_lockdep_assert_held_rcu_node(rnp);
if (qovld_calc <= 0)
return; // Early boot and wildcard value set.
if (rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc)
WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask | rdp->grpmask);
else
WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask & ~rdp->grpmask);
}
/*
* Check and if necessary update the leaf rcu_node structure's
* ->cbovldmask bit corresponding to the current CPU based on that CPU's
* number of queued RCU callbacks. No locks need be held, but the
* caller must have disabled interrupts.
*
* Note that this function ignores the possibility that there are a lot
* of callbacks all of which have already seen the end of their respective
* grace periods. This omission is due to the need for no-CBs CPUs to
* be holding ->nocb_lock to do this check, which is too heavy for a
* common-case operation.
*/
static void check_cb_ovld(struct rcu_data *rdp)
{
struct rcu_node *const rnp = rdp->mynode;
if (qovld_calc <= 0 ||
((rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc) ==
!!(READ_ONCE(rnp->cbovldmask) & rdp->grpmask)))
return; // Early boot wildcard value or already set correctly.
raw_spin_lock_rcu_node(rnp);
check_cb_ovld_locked(rdp, rnp);
raw_spin_unlock_rcu_node(rnp);
}
static void
__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in)
{
static atomic_t doublefrees;
unsigned long flags;
bool lazy;
struct rcu_data *rdp;
bool was_alldone;
/* Misaligned rcu_head! */
WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
if (debug_rcu_head_queue(head)) {
/*
* Probable double call_rcu(), so leak the callback.
* Use rcu:rcu_callback trace event to find the previous
* time callback was passed to call_rcu().
*/
if (atomic_inc_return(&doublefrees) < 4) {
pr_err("%s(): Double-freed CB %p->%pS()!!! ", __func__, head, head->func);
mem_dump_obj(head);
}
WRITE_ONCE(head->func, rcu_leak_callback);
return;
}
head->func = func;
head->next = NULL;
kasan_record_aux_stack_noalloc(head);
local_irq_save(flags);
rdp = this_cpu_ptr(&rcu_data);
lazy = lazy_in && !rcu_async_should_hurry();
/* Add the callback to our list. */
if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist))) {
// This can trigger due to call_rcu() from offline CPU:
WARN_ON_ONCE(rcu_scheduler_active != RCU_SCHEDULER_INACTIVE);
WARN_ON_ONCE(!rcu_is_watching());
// Very early boot, before rcu_init(). Initialize if needed
// and then drop through to queue the callback.
if (rcu_segcblist_empty(&rdp->cblist))
rcu_segcblist_init(&rdp->cblist);
}
check_cb_ovld(rdp);
if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags, lazy))
return; // Enqueued onto ->nocb_bypass, so just leave.
// If no-CBs CPU gets here, rcu_nocb_try_bypass() acquired ->nocb_lock.
rcu_segcblist_enqueue(&rdp->cblist, head);
if (__is_kvfree_rcu_offset((unsigned long)func))
trace_rcu_kvfree_callback(rcu_state.name, head,
(unsigned long)func,
rcu_segcblist_n_cbs(&rdp->cblist));
else
trace_rcu_callback(rcu_state.name, head,
rcu_segcblist_n_cbs(&rdp->cblist));
trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCBQueued"));
/* Go handle any RCU core processing required. */
if (unlikely(rcu_rdp_is_offloaded(rdp))) {
__call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */
} else {
__call_rcu_core(rdp, head, flags);
local_irq_restore(flags);
}
}
#ifdef CONFIG_RCU_LAZY
/**
* call_rcu_hurry() - Queue RCU callback for invocation after grace period, and
* flush all lazy callbacks (including the new one) to the main ->cblist while
* doing so.
*
* @head: structure to be used for queueing the RCU updates.
* @func: actual callback function to be invoked after the grace period
*
* The callback function will be invoked some time after a full grace
* period elapses, in other words after all pre-existing RCU read-side
* critical sections have completed.
*
* Use this API instead of call_rcu() if you don't want the callback to be
* invoked after very long periods of time, which can happen on systems without
* memory pressure and on systems which are lightly loaded or mostly idle.
* This function will cause callbacks to be invoked sooner than later at the
* expense of extra power. Other than that, this function is identical to, and
* reuses call_rcu()'s logic. Refer to call_rcu() for more details about memory
* ordering and other functionality.
*/
void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func)
{
return __call_rcu_common(head, func, false);
}
EXPORT_SYMBOL_GPL(call_rcu_hurry);
#endif
/**
* call_rcu() - Queue an RCU callback for invocation after a grace period.
* By default the callbacks are 'lazy' and are kept hidden from the main
* ->cblist to prevent starting of grace periods too soon.
* If you desire grace periods to start very soon, use call_rcu_hurry().
*
* @head: structure to be used for queueing the RCU updates.
* @func: actual callback function to be invoked after the grace period
*
* The callback function will be invoked some time after a full grace
* period elapses, in other words after all pre-existing RCU read-side
* critical sections have completed. However, the callback function
* might well execute concurrently with RCU read-side critical sections
* that started after call_rcu() was invoked.
*
* RCU read-side critical sections are delimited by rcu_read_lock()
* and rcu_read_unlock(), and may be nested. In addition, but only in
* v5.0 and later, regions of code across which interrupts, preemption,
* or softirqs have been disabled also serve as RCU read-side critical
* sections. This includes hardware interrupt handlers, softirq handlers,
* and NMI handlers.
*
* Note that all CPUs must agree that the grace period extended beyond
* all pre-existing RCU read-side critical section. On systems with more
* than one CPU, this means that when "func()" is invoked, each CPU is
* guaranteed to have executed a full memory barrier since the end of its
* last RCU read-side critical section whose beginning preceded the call
* to call_rcu(). It also means that each CPU executing an RCU read-side
* critical section that continues beyond the start of "func()" must have
* executed a memory barrier after the call_rcu() but before the beginning
* of that RCU read-side critical section. Note that these guarantees
* include CPUs that are offline, idle, or executing in user mode, as
* well as CPUs that are executing in the kernel.
*
* Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
* resulting RCU callback function "func()", then both CPU A and CPU B are
* guaranteed to execute a full memory barrier during the time interval
* between the call to call_rcu() and the invocation of "func()" -- even
* if CPU A and CPU B are the same CPU (but again only if the system has
* more than one CPU).
*
* Implementation of these memory-ordering guarantees is described here:
* Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
*/
void call_rcu(struct rcu_head *head, rcu_callback_t func)
{
return __call_rcu_common(head, func, IS_ENABLED(CONFIG_RCU_LAZY));
}
EXPORT_SYMBOL_GPL(call_rcu);
/* Maximum number of jiffies to wait before draining a batch. */
#define KFREE_DRAIN_JIFFIES (5 * HZ)
#define KFREE_N_BATCHES 2
#define FREE_N_CHANNELS 2
/**
* struct kvfree_rcu_bulk_data - single block to store kvfree_rcu() pointers
* @list: List node. All blocks are linked between each other
* @gp_snap: Snapshot of RCU state for objects placed to this bulk
* @nr_records: Number of active pointers in the array
* @records: Array of the kvfree_rcu() pointers
*/
struct kvfree_rcu_bulk_data {
struct list_head list;
unsigned long gp_snap;
unsigned long nr_records;
void *records[];
};
/*
* This macro defines how many entries the "records" array
* will contain. It is based on the fact that the size of
* kvfree_rcu_bulk_data structure becomes exactly one page.
*/
#define KVFREE_BULK_MAX_ENTR \
((PAGE_SIZE - sizeof(struct kvfree_rcu_bulk_data)) / sizeof(void *))
/**
* struct kfree_rcu_cpu_work - single batch of kfree_rcu() requests
* @rcu_work: Let queue_rcu_work() invoke workqueue handler after grace period
* @head_free: List of kfree_rcu() objects waiting for a grace period
* @bulk_head_free: Bulk-List of kvfree_rcu() objects waiting for a grace period
* @krcp: Pointer to @kfree_rcu_cpu structure
*/
struct kfree_rcu_cpu_work {
struct rcu_work rcu_work;
struct rcu_head *head_free;
struct list_head bulk_head_free[FREE_N_CHANNELS];
struct kfree_rcu_cpu *krcp;
};
/**
* struct kfree_rcu_cpu - batch up kfree_rcu() requests for RCU grace period
* @head: List of kfree_rcu() objects not yet waiting for a grace period
* @head_gp_snap: Snapshot of RCU state for objects placed to "@head"
* @bulk_head: Bulk-List of kvfree_rcu() objects not yet waiting for a grace period
* @krw_arr: Array of batches of kfree_rcu() objects waiting for a grace period
* @lock: Synchronize access to this structure
* @monitor_work: Promote @head to @head_free after KFREE_DRAIN_JIFFIES
* @initialized: The @rcu_work fields have been initialized
* @head_count: Number of objects in rcu_head singular list
* @bulk_count: Number of objects in bulk-list
* @bkvcache:
* A simple cache list that contains objects for reuse purpose.
* In order to save some per-cpu space the list is singular.
* Even though it is lockless an access has to be protected by the
* per-cpu lock.
* @page_cache_work: A work to refill the cache when it is empty
* @backoff_page_cache_fill: Delay cache refills
* @work_in_progress: Indicates that page_cache_work is running
* @hrtimer: A hrtimer for scheduling a page_cache_work
* @nr_bkv_objs: number of allocated objects at @bkvcache.
*
* This is a per-CPU structure. The reason that it is not included in
* the rcu_data structure is to permit this code to be extracted from
* the RCU files. Such extraction could allow further optimization of
* the interactions with the slab allocators.
*/
struct kfree_rcu_cpu {
// Objects queued on a linked list
// through their rcu_head structures.
struct rcu_head *head;
unsigned long head_gp_snap;
atomic_t head_count;
// Objects queued on a bulk-list.
struct list_head bulk_head[FREE_N_CHANNELS];
atomic_t bulk_count[FREE_N_CHANNELS];
struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES];
raw_spinlock_t lock;
struct delayed_work monitor_work;
bool initialized;
struct delayed_work page_cache_work;
atomic_t backoff_page_cache_fill;
atomic_t work_in_progress;
struct hrtimer hrtimer;
struct llist_head bkvcache;
int nr_bkv_objs;
};
static DEFINE_PER_CPU(struct kfree_rcu_cpu, krc) = {
.lock = __RAW_SPIN_LOCK_UNLOCKED(krc.lock),
};
static __always_inline void
debug_rcu_bhead_unqueue(struct kvfree_rcu_bulk_data *bhead)
{
#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
int i;
for (i = 0; i < bhead->nr_records; i++)
debug_rcu_head_unqueue((struct rcu_head *)(bhead->records[i]));
#endif
}
static inline struct kfree_rcu_cpu *
krc_this_cpu_lock(unsigned long *flags)
{
struct kfree_rcu_cpu *krcp;
local_irq_save(*flags); // For safely calling this_cpu_ptr().
krcp = this_cpu_ptr(&krc);
raw_spin_lock(&krcp->lock);
return krcp;
}
static inline void
krc_this_cpu_unlock(struct kfree_rcu_cpu *krcp, unsigned long flags)
{
raw_spin_unlock_irqrestore(&krcp->lock, flags);
}
static inline struct kvfree_rcu_bulk_data *
get_cached_bnode(struct kfree_rcu_cpu *krcp)
{
if (!krcp->nr_bkv_objs)
return NULL;
WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs - 1);
return (struct kvfree_rcu_bulk_data *)
llist_del_first(&krcp->bkvcache);
}
static inline bool
put_cached_bnode(struct kfree_rcu_cpu *krcp,
struct kvfree_rcu_bulk_data *bnode)
{
// Check the limit.
if (krcp->nr_bkv_objs >= rcu_min_cached_objs)
return false;
llist_add((struct llist_node *) bnode, &krcp->bkvcache);
WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs + 1);
return true;
}
static int
drain_page_cache(struct kfree_rcu_cpu *krcp)
{
unsigned long flags;
struct llist_node *page_list, *pos, *n;
int freed = 0;
raw_spin_lock_irqsave(&krcp->lock, flags);
page_list = llist_del_all(&krcp->bkvcache);
WRITE_ONCE(krcp->nr_bkv_objs, 0);
raw_spin_unlock_irqrestore(&krcp->lock, flags);
llist_for_each_safe(pos, n, page_list) {
free_page((unsigned long)pos);
freed++;
}
return freed;
}
static void
kvfree_rcu_bulk(struct kfree_rcu_cpu *krcp,
struct kvfree_rcu_bulk_data *bnode, int idx)
{
unsigned long flags;
int i;
debug_rcu_bhead_unqueue(bnode);
rcu_lock_acquire(&rcu_callback_map);
if (idx == 0) { // kmalloc() / kfree().
trace_rcu_invoke_kfree_bulk_callback(
rcu_state.name, bnode->nr_records,
bnode->records);
kfree_bulk(bnode->nr_records, bnode->records);
} else { // vmalloc() / vfree().
for (i = 0; i < bnode->nr_records; i++) {
trace_rcu_invoke_kvfree_callback(
rcu_state.name, bnode->records[i], 0);
vfree(bnode->records[i]);
}
}
rcu_lock_release(&rcu_callback_map);
raw_spin_lock_irqsave(&krcp->lock, flags);
if (put_cached_bnode(krcp, bnode))
bnode = NULL;
raw_spin_unlock_irqrestore(&krcp->lock, flags);
if (bnode)
free_page((unsigned long) bnode);
cond_resched_tasks_rcu_qs();
}
static void
kvfree_rcu_list(struct rcu_head *head)
{
struct rcu_head *next;
for (; head; head = next) {
void *ptr = (void *) head->func;
unsigned long offset = (void *) head - ptr;
next = head->next;
debug_rcu_head_unqueue((struct rcu_head *)ptr);
rcu_lock_acquire(&rcu_callback_map);
trace_rcu_invoke_kvfree_callback(rcu_state.name, head, offset);
if (!WARN_ON_ONCE(!__is_kvfree_rcu_offset(offset)))
kvfree(ptr);
rcu_lock_release(&rcu_callback_map);
cond_resched_tasks_rcu_qs();
}
}
/*
* This function is invoked in workqueue context after a grace period.
* It frees all the objects queued on ->bulk_head_free or ->head_free.
*/
static void kfree_rcu_work(struct work_struct *work)
{
unsigned long flags;
struct kvfree_rcu_bulk_data *bnode, *n;
struct list_head bulk_head[FREE_N_CHANNELS];
struct rcu_head *head;
struct kfree_rcu_cpu *krcp;
struct kfree_rcu_cpu_work *krwp;
int i;
krwp = container_of(to_rcu_work(work),
struct kfree_rcu_cpu_work, rcu_work);
krcp = krwp->krcp;
raw_spin_lock_irqsave(&krcp->lock, flags);
// Channels 1 and 2.
for (i = 0; i < FREE_N_CHANNELS; i++)
list_replace_init(&krwp->bulk_head_free[i], &bulk_head[i]);
// Channel 3.
head = krwp->head_free;
krwp->head_free = NULL;
raw_spin_unlock_irqrestore(&krcp->lock, flags);
// Handle the first two channels.
for (i = 0; i < FREE_N_CHANNELS; i++) {
// Start from the tail page, so a GP is likely passed for it.
list_for_each_entry_safe(bnode, n, &bulk_head[i], list)
kvfree_rcu_bulk(krcp, bnode, i);
}
/*
* This is used when the "bulk" path can not be used for the
* double-argument of kvfree_rcu(). This happens when the
* page-cache is empty, which means that objects are instead
* queued on a linked list through their rcu_head structures.
* This list is named "Channel 3".
*/
kvfree_rcu_list(head);
}
static bool
need_offload_krc(struct kfree_rcu_cpu *krcp)
{
int i;
for (i = 0; i < FREE_N_CHANNELS; i++)
if (!list_empty(&krcp->bulk_head[i]))
return true;
return !!READ_ONCE(krcp->head);
}
static bool
need_wait_for_krwp_work(struct kfree_rcu_cpu_work *krwp)
{
int i;
for (i = 0; i < FREE_N_CHANNELS; i++)
if (!list_empty(&krwp->bulk_head_free[i]))
return true;
return !!krwp->head_free;
}
static int krc_count(struct kfree_rcu_cpu *krcp)
{
int sum = atomic_read(&krcp->head_count);
int i;
for (i = 0; i < FREE_N_CHANNELS; i++)
sum += atomic_read(&krcp->bulk_count[i]);
return sum;
}
static void
schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp)
{
long delay, delay_left;
delay = krc_count(krcp) >= KVFREE_BULK_MAX_ENTR ? 1:KFREE_DRAIN_JIFFIES;
if (delayed_work_pending(&krcp->monitor_work)) {
delay_left = krcp->monitor_work.timer.expires - jiffies;
if (delay < delay_left)
mod_delayed_work(system_wq, &krcp->monitor_work, delay);
return;
}
queue_delayed_work(system_wq, &krcp->monitor_work, delay);
}
static void
kvfree_rcu_drain_ready(struct kfree_rcu_cpu *krcp)
{
struct list_head bulk_ready[FREE_N_CHANNELS];
struct kvfree_rcu_bulk_data *bnode, *n;
struct rcu_head *head_ready = NULL;
unsigned long flags;
int i;
raw_spin_lock_irqsave(&krcp->lock, flags);
for (i = 0; i < FREE_N_CHANNELS; i++) {
INIT_LIST_HEAD(&bulk_ready[i]);
list_for_each_entry_safe_reverse(bnode, n, &krcp->bulk_head[i], list) {
if (!poll_state_synchronize_rcu(bnode->gp_snap))
break;
atomic_sub(bnode->nr_records, &krcp->bulk_count[i]);
list_move(&bnode->list, &bulk_ready[i]);
}
}
if (krcp->head && poll_state_synchronize_rcu(krcp->head_gp_snap)) {
head_ready = krcp->head;
atomic_set(&krcp->head_count, 0);
WRITE_ONCE(krcp->head, NULL);
}
raw_spin_unlock_irqrestore(&krcp->lock, flags);
for (i = 0; i < FREE_N_CHANNELS; i++) {
list_for_each_entry_safe(bnode, n, &bulk_ready[i], list)
kvfree_rcu_bulk(krcp, bnode, i);
}
if (head_ready)
kvfree_rcu_list(head_ready);
}
/*
* This function is invoked after the KFREE_DRAIN_JIFFIES timeout.
*/
static void kfree_rcu_monitor(struct work_struct *work)
{
struct kfree_rcu_cpu *krcp = container_of(work,
struct kfree_rcu_cpu, monitor_work.work);
unsigned long flags;
int i, j;
// Drain ready for reclaim.
kvfree_rcu_drain_ready(krcp);
raw_spin_lock_irqsave(&krcp->lock, flags);
// Attempt to start a new batch.
for (i = 0; i < KFREE_N_BATCHES; i++) {
struct kfree_rcu_cpu_work *krwp = &(krcp->krw_arr[i]);
// Try to detach bulk_head or head and attach it, only when
// all channels are free. Any channel is not free means at krwp
// there is on-going rcu work to handle krwp's free business.
if (need_wait_for_krwp_work(krwp))
continue;
// kvfree_rcu_drain_ready() might handle this krcp, if so give up.
if (need_offload_krc(krcp)) {
// Channel 1 corresponds to the SLAB-pointer bulk path.
// Channel 2 corresponds to vmalloc-pointer bulk path.
for (j = 0; j < FREE_N_CHANNELS; j++) {
if (list_empty(&krwp->bulk_head_free[j])) {
atomic_set(&krcp->bulk_count[j], 0);
list_replace_init(&krcp->bulk_head[j],
&krwp->bulk_head_free[j]);
}
}
// Channel 3 corresponds to both SLAB and vmalloc
// objects queued on the linked list.
if (!krwp->head_free) {
krwp->head_free = krcp->head;
atomic_set(&krcp->head_count, 0);
WRITE_ONCE(krcp->head, NULL);
}
// One work is per one batch, so there are three
// "free channels", the batch can handle. It can
// be that the work is in the pending state when
// channels have been detached following by each
// other.
queue_rcu_work(system_wq, &krwp->rcu_work);
}
}
raw_spin_unlock_irqrestore(&krcp->lock, flags);
// If there is nothing to detach, it means that our job is
// successfully done here. In case of having at least one
// of the channels that is still busy we should rearm the
// work to repeat an attempt. Because previous batches are
// still in progress.
if (need_offload_krc(krcp))
schedule_delayed_monitor_work(krcp);
}
static enum hrtimer_restart
schedule_page_work_fn(struct hrtimer *t)
{
struct kfree_rcu_cpu *krcp =
container_of(t, struct kfree_rcu_cpu, hrtimer);
queue_delayed_work(system_highpri_wq, &krcp->page_cache_work, 0);
return HRTIMER_NORESTART;
}
static void fill_page_cache_func(struct work_struct *work)
{
struct kvfree_rcu_bulk_data *bnode;
struct kfree_rcu_cpu *krcp =
container_of(work, struct kfree_rcu_cpu,
page_cache_work.work);
unsigned long flags;
int nr_pages;
bool pushed;
int i;
nr_pages = atomic_read(&krcp->backoff_page_cache_fill) ?
1 : rcu_min_cached_objs;
for (i = 0; i < nr_pages; i++) {
bnode = (struct kvfree_rcu_bulk_data *)
__get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
if (!bnode)
break;
raw_spin_lock_irqsave(&krcp->lock, flags);
pushed = put_cached_bnode(krcp, bnode);
raw_spin_unlock_irqrestore(&krcp->lock, flags);
if (!pushed) {
free_page((unsigned long) bnode);
break;
}
}
atomic_set(&krcp->work_in_progress, 0);
atomic_set(&krcp->backoff_page_cache_fill, 0);
}
static void
run_page_cache_worker(struct kfree_rcu_cpu *krcp)
{
if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING &&
!atomic_xchg(&krcp->work_in_progress, 1)) {
if (atomic_read(&krcp->backoff_page_cache_fill)) {
queue_delayed_work(system_wq,
&krcp->page_cache_work,
msecs_to_jiffies(rcu_delay_page_cache_fill_msec));
} else {
hrtimer_init(&krcp->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
krcp->hrtimer.function = schedule_page_work_fn;
hrtimer_start(&krcp->hrtimer, 0, HRTIMER_MODE_REL);
}
}
}
// Record ptr in a page managed by krcp, with the pre-krc_this_cpu_lock()
// state specified by flags. If can_alloc is true, the caller must
// be schedulable and not be holding any locks or mutexes that might be
// acquired by the memory allocator or anything that it might invoke.
// Returns true if ptr was successfully recorded, else the caller must
// use a fallback.
static inline bool
add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp,
unsigned long *flags, void *ptr, bool can_alloc)
{
struct kvfree_rcu_bulk_data *bnode;
int idx;
*krcp = krc_this_cpu_lock(flags);
if (unlikely(!(*krcp)->initialized))
return false;
idx = !!is_vmalloc_addr(ptr);
bnode = list_first_entry_or_null(&(*krcp)->bulk_head[idx],
struct kvfree_rcu_bulk_data, list);
/* Check if a new block is required. */
if (!bnode || bnode->nr_records == KVFREE_BULK_MAX_ENTR) {
bnode = get_cached_bnode(*krcp);
if (!bnode && can_alloc) {
krc_this_cpu_unlock(*krcp, *flags);
// __GFP_NORETRY - allows a light-weight direct reclaim
// what is OK from minimizing of fallback hitting point of
// view. Apart of that it forbids any OOM invoking what is
// also beneficial since we are about to release memory soon.
//
// __GFP_NOMEMALLOC - prevents from consuming of all the
// memory reserves. Please note we have a fallback path.
//
// __GFP_NOWARN - it is supposed that an allocation can
// be failed under low memory or high memory pressure
// scenarios.
bnode = (struct kvfree_rcu_bulk_data *)
__get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
*krcp = krc_this_cpu_lock(flags);
}
if (!bnode)
return false;
// Initialize the new block and attach it.
bnode->nr_records = 0;
list_add(&bnode->list, &(*krcp)->bulk_head[idx]);
}
// Finally insert and update the GP for this page.
bnode->records[bnode->nr_records++] = ptr;
bnode->gp_snap = get_state_synchronize_rcu();
atomic_inc(&(*krcp)->bulk_count[idx]);
return true;
}
/*
* Queue a request for lazy invocation of the appropriate free routine
* after a grace period. Please note that three paths are maintained,
* two for the common case using arrays of pointers and a third one that
* is used only when the main paths cannot be used, for example, due to
* memory pressure.
*
* Each kvfree_call_rcu() request is added to a batch. The batch will be drained
* every KFREE_DRAIN_JIFFIES number of jiffies. All the objects in the batch will
* be free'd in workqueue context. This allows us to: batch requests together to
* reduce the number of grace periods during heavy kfree_rcu()/kvfree_rcu() load.
*/
void kvfree_call_rcu(struct rcu_head *head, void *ptr)
{
unsigned long flags;
struct kfree_rcu_cpu *krcp;
bool success;
/*
* Please note there is a limitation for the head-less
* variant, that is why there is a clear rule for such
* objects: it can be used from might_sleep() context
* only. For other places please embed an rcu_head to
* your data.
*/
if (!head)
might_sleep();
// Queue the object but don't yet schedule the batch.
if (debug_rcu_head_queue(ptr)) {
// Probable double kfree_rcu(), just leak.
WARN_ONCE(1, "%s(): Double-freed call. rcu_head %p\n",
__func__, head);
// Mark as success and leave.
return;
}
kasan_record_aux_stack_noalloc(ptr);
success = add_ptr_to_bulk_krc_lock(&krcp, &flags, ptr, !head);
if (!success) {
run_page_cache_worker(krcp);
if (head == NULL)
// Inline if kvfree_rcu(one_arg) call.
goto unlock_return;
head->func = ptr;
head->next = krcp->head;
WRITE_ONCE(krcp->head, head);
atomic_inc(&krcp->head_count);
// Take a snapshot for this krcp.
krcp->head_gp_snap = get_state_synchronize_rcu();
success = true;
}
// Set timer to drain after KFREE_DRAIN_JIFFIES.
if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING)
schedule_delayed_monitor_work(krcp);
unlock_return:
krc_this_cpu_unlock(krcp, flags);
/*
* Inline kvfree() after synchronize_rcu(). We can do
* it from might_sleep() context only, so the current
* CPU can pass the QS state.
*/
if (!success) {
debug_rcu_head_unqueue((struct rcu_head *) ptr);
synchronize_rcu();
kvfree(ptr);
}
}
EXPORT_SYMBOL_GPL(kvfree_call_rcu);
static unsigned long
kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
{
int cpu;
unsigned long count = 0;
/* Snapshot count of all CPUs */
for_each_possible_cpu(cpu) {
struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
count += krc_count(krcp);
count += READ_ONCE(krcp->nr_bkv_objs);
atomic_set(&krcp->backoff_page_cache_fill, 1);
}
return count == 0 ? SHRINK_EMPTY : count;
}
static unsigned long
kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
{
int cpu, freed = 0;
for_each_possible_cpu(cpu) {
int count;
struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
count = krc_count(krcp);
count += drain_page_cache(krcp);
kfree_rcu_monitor(&krcp->monitor_work.work);
sc->nr_to_scan -= count;
freed += count;
if (sc->nr_to_scan <= 0)
break;
}
return freed == 0 ? SHRINK_STOP : freed;
}
static struct shrinker kfree_rcu_shrinker = {
.count_objects = kfree_rcu_shrink_count,
.scan_objects = kfree_rcu_shrink_scan,
.batch = 0,
.seeks = DEFAULT_SEEKS,
};
void __init kfree_rcu_scheduler_running(void)
{
int cpu;
for_each_possible_cpu(cpu) {
struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
if (need_offload_krc(krcp))
schedule_delayed_monitor_work(krcp);
}
}
/*
* During early boot, any blocking grace-period wait automatically
* implies a grace period.
*
* Later on, this could in theory be the case for kernels built with
* CONFIG_SMP=y && CONFIG_PREEMPTION=y running on a single CPU, but this
* is not a common case. Furthermore, this optimization would cause
* the rcu_gp_oldstate structure to expand by 50%, so this potential
* grace-period optimization is ignored once the scheduler is running.
*/
static int rcu_blocking_is_gp(void)
{
if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE) {
might_sleep();
return false;
}
return true;
}
/**
* synchronize_rcu - wait until a grace period has elapsed.
*
* Control will return to the caller some time after a full grace
* period has elapsed, in other words after all currently executing RCU
* read-side critical sections have completed. Note, however, that
* upon return from synchronize_rcu(), the caller might well be executing
* concurrently with new RCU read-side critical sections that began while
* synchronize_rcu() was waiting.
*
* RCU read-side critical sections are delimited by rcu_read_lock()
* and rcu_read_unlock(), and may be nested. In addition, but only in
* v5.0 and later, regions of code across which interrupts, preemption,
* or softirqs have been disabled also serve as RCU read-side critical
* sections. This includes hardware interrupt handlers, softirq handlers,
* and NMI handlers.
*
* Note that this guarantee implies further memory-ordering guarantees.
* On systems with more than one CPU, when synchronize_rcu() returns,
* each CPU is guaranteed to have executed a full memory barrier since
* the end of its last RCU read-side critical section whose beginning
* preceded the call to synchronize_rcu(). In addition, each CPU having
* an RCU read-side critical section that extends beyond the return from
* synchronize_rcu() is guaranteed to have executed a full memory barrier
* after the beginning of synchronize_rcu() and before the beginning of
* that RCU read-side critical section. Note that these guarantees include
* CPUs that are offline, idle, or executing in user mode, as well as CPUs
* that are executing in the kernel.
*
* Furthermore, if CPU A invoked synchronize_rcu(), which returned
* to its caller on CPU B, then both CPU A and CPU B are guaranteed
* to have executed a full memory barrier during the execution of
* synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but
* again only if the system has more than one CPU).
*
* Implementation of these memory-ordering guarantees is described here:
* Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
*/
void synchronize_rcu(void)
{
unsigned long flags;
struct rcu_node *rnp;
RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
lock_is_held(&rcu_lock_map) ||
lock_is_held(&rcu_sched_lock_map),
"Illegal synchronize_rcu() in RCU read-side critical section");
if (!rcu_blocking_is_gp()) {
if (rcu_gp_is_expedited())
synchronize_rcu_expedited();
else
wait_rcu_gp(call_rcu_hurry);
return;
}
// Context allows vacuous grace periods.
// Note well that this code runs with !PREEMPT && !SMP.
// In addition, all code that advances grace periods runs at
// process level. Therefore, this normal GP overlaps with other
// normal GPs only by being fully nested within them, which allows
// reuse of ->gp_seq_polled_snap.
rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_snap);
rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_snap);
// Update the normal grace-period counters to record
// this grace period, but only those used by the boot CPU.
// The rcu_scheduler_starting() will take care of the rest of
// these counters.
local_irq_save(flags);
WARN_ON_ONCE(num_online_cpus() > 1);
rcu_state.gp_seq += (1 << RCU_SEQ_CTR_SHIFT);
for (rnp = this_cpu_ptr(&rcu_data)->mynode; rnp; rnp = rnp->parent)
rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq;
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(synchronize_rcu);
/**
* get_completed_synchronize_rcu_full - Return a full pre-completed polled state cookie
* @rgosp: Place to put state cookie
*
* Stores into @rgosp a value that will always be treated by functions
* like poll_state_synchronize_rcu_full() as a cookie whose grace period
* has already completed.
*/
void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
{
rgosp->rgos_norm = RCU_GET_STATE_COMPLETED;
rgosp->rgos_exp = RCU_GET_STATE_COMPLETED;
}
EXPORT_SYMBOL_GPL(get_completed_synchronize_rcu_full);
/**
* get_state_synchronize_rcu - Snapshot current RCU state
*
* Returns a cookie that is used by a later call to cond_synchronize_rcu()
* or poll_state_synchronize_rcu() to determine whether or not a full
* grace period has elapsed in the meantime.
*/
unsigned long get_state_synchronize_rcu(void)
{
/*
* Any prior manipulation of RCU-protected data must happen
* before the load from ->gp_seq.
*/
smp_mb(); /* ^^^ */
return rcu_seq_snap(&rcu_state.gp_seq_polled);
}
EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
/**
* get_state_synchronize_rcu_full - Snapshot RCU state, both normal and expedited
* @rgosp: location to place combined normal/expedited grace-period state
*
* Places the normal and expedited grace-period states in @rgosp. This
* state value can be passed to a later call to cond_synchronize_rcu_full()
* or poll_state_synchronize_rcu_full() to determine whether or not a
* grace period (whether normal or expedited) has elapsed in the meantime.
* The rcu_gp_oldstate structure takes up twice the memory of an unsigned
* long, but is guaranteed to see all grace periods. In contrast, the
* combined state occupies less memory, but can sometimes fail to take
* grace periods into account.
*
* This does not guarantee that the needed grace period will actually
* start.
*/
void get_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
{
struct rcu_node *rnp = rcu_get_root();
/*
* Any prior manipulation of RCU-protected data must happen
* before the loads from ->gp_seq and ->expedited_sequence.
*/
smp_mb(); /* ^^^ */
rgosp->rgos_norm = rcu_seq_snap(&rnp->gp_seq);
rgosp->rgos_exp = rcu_seq_snap(&rcu_state.expedited_sequence);
}
EXPORT_SYMBOL_GPL(get_state_synchronize_rcu_full);
/*
* Helper function for start_poll_synchronize_rcu() and
* start_poll_synchronize_rcu_full().
*/
static void start_poll_synchronize_rcu_common(void)
{
unsigned long flags;
bool needwake;
struct rcu_data *rdp;
struct rcu_node *rnp;
lockdep_assert_irqs_enabled();
local_irq_save(flags);
rdp = this_cpu_ptr(&rcu_data);
rnp = rdp->mynode;
raw_spin_lock_rcu_node(rnp); // irqs already disabled.
// Note it is possible for a grace period to have elapsed between
// the above call to get_state_synchronize_rcu() and the below call
// to rcu_seq_snap. This is OK, the worst that happens is that we
// get a grace period that no one needed. These accesses are ordered
// by smp_mb(), and we are accessing them in the opposite order
// from which they are updated at grace-period start, as required.
needwake = rcu_start_this_gp(rnp, rdp, rcu_seq_snap(&rcu_state.gp_seq));
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
if (needwake)
rcu_gp_kthread_wake();
}
/**
* start_poll_synchronize_rcu - Snapshot and start RCU grace period
*
* Returns a cookie that is used by a later call to cond_synchronize_rcu()
* or poll_state_synchronize_rcu() to determine whether or not a full
* grace period has elapsed in the meantime. If the needed grace period
* is not already slated to start, notifies RCU core of the need for that
* grace period.
*
* Interrupts must be enabled for the case where it is necessary to awaken
* the grace-period kthread.
*/
unsigned long start_poll_synchronize_rcu(void)
{
unsigned long gp_seq = get_state_synchronize_rcu();
start_poll_synchronize_rcu_common();
return gp_seq;
}
EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu);
/**
* start_poll_synchronize_rcu_full - Take a full snapshot and start RCU grace period
* @rgosp: value from get_state_synchronize_rcu_full() or start_poll_synchronize_rcu_full()
*
* Places the normal and expedited grace-period states in *@rgos. This
* state value can be passed to a later call to cond_synchronize_rcu_full()
* or poll_state_synchronize_rcu_full() to determine whether or not a
* grace period (whether normal or expedited) has elapsed in the meantime.
* If the needed grace period is not already slated to start, notifies
* RCU core of the need for that grace period.
*
* Interrupts must be enabled for the case where it is necessary to awaken
* the grace-period kthread.
*/
void start_poll_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
{
get_state_synchronize_rcu_full(rgosp);
start_poll_synchronize_rcu_common();
}
EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_full);
/**
* poll_state_synchronize_rcu - Has the specified RCU grace period completed?
* @oldstate: value from get_state_synchronize_rcu() or start_poll_synchronize_rcu()
*
* If a full RCU grace period has elapsed since the earlier call from
* which @oldstate was obtained, return @true, otherwise return @false.
* If @false is returned, it is the caller's responsibility to invoke this
* function later on until it does return @true. Alternatively, the caller
* can explicitly wait for a grace period, for example, by passing @oldstate
* to either cond_synchronize_rcu() or cond_synchronize_rcu_expedited()
* on the one hand or by directly invoking either synchronize_rcu() or
* synchronize_rcu_expedited() on the other.
*
* Yes, this function does not take counter wrap into account.
* But counter wrap is harmless. If the counter wraps, we have waited for
* more than a billion grace periods (and way more on a 64-bit system!).
* Those needing to keep old state values for very long time periods
* (many hours even on 32-bit systems) should check them occasionally and
* either refresh them or set a flag indicating that the grace period has
* completed. Alternatively, they can use get_completed_synchronize_rcu()
* to get a guaranteed-completed grace-period state.
*
* In addition, because oldstate compresses the grace-period state for
* both normal and expedited grace periods into a single unsigned long,
* it can miss a grace period when synchronize_rcu() runs concurrently
* with synchronize_rcu_expedited(). If this is unacceptable, please
* instead use the _full() variant of these polling APIs.
*
* This function provides the same memory-ordering guarantees that
* would be provided by a synchronize_rcu() that was invoked at the call
* to the function that provided @oldstate, and that returned at the end
* of this function.
*/
bool poll_state_synchronize_rcu(unsigned long oldstate)
{
if (oldstate == RCU_GET_STATE_COMPLETED ||
rcu_seq_done_exact(&rcu_state.gp_seq_polled, oldstate)) {
smp_mb(); /* Ensure GP ends before subsequent accesses. */
return true;
}
return false;
}
EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
/**
* poll_state_synchronize_rcu_full - Has the specified RCU grace period completed?
* @rgosp: value from get_state_synchronize_rcu_full() or start_poll_synchronize_rcu_full()
*
* If a full RCU grace period has elapsed since the earlier call from
* which *rgosp was obtained, return @true, otherwise return @false.
* If @false is returned, it is the caller's responsibility to invoke this
* function later on until it does return @true. Alternatively, the caller
* can explicitly wait for a grace period, for example, by passing @rgosp
* to cond_synchronize_rcu() or by directly invoking synchronize_rcu().
*
* Yes, this function does not take counter wrap into account.
* But counter wrap is harmless. If the counter wraps, we have waited
* for more than a billion grace periods (and way more on a 64-bit
* system!). Those needing to keep rcu_gp_oldstate values for very
* long time periods (many hours even on 32-bit systems) should check
* them occasionally and either refresh them or set a flag indicating
* that the grace period has completed. Alternatively, they can use
* get_completed_synchronize_rcu_full() to get a guaranteed-completed
* grace-period state.
*
* This function provides the same memory-ordering guarantees that would
* be provided by a synchronize_rcu() that was invoked at the call to
* the function that provided @rgosp, and that returned at the end of this
* function. And this guarantee requires that the root rcu_node structure's
* ->gp_seq field be checked instead of that of the rcu_state structure.
* The problem is that the just-ending grace-period's callbacks can be
* invoked between the time that the root rcu_node structure's ->gp_seq
* field is updated and the time that the rcu_state structure's ->gp_seq
* field is updated. Therefore, if a single synchronize_rcu() is to
* cause a subsequent poll_state_synchronize_rcu_full() to return @true,
* then the root rcu_node structure is the one that needs to be polled.
*/
bool poll_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
{
struct rcu_node *rnp = rcu_get_root();
smp_mb(); // Order against root rcu_node structure grace-period cleanup.
if (rgosp->rgos_norm == RCU_GET_STATE_COMPLETED ||
rcu_seq_done_exact(&rnp->gp_seq, rgosp->rgos_norm) ||
rgosp->rgos_exp == RCU_GET_STATE_COMPLETED ||
rcu_seq_done_exact(&rcu_state.expedited_sequence, rgosp->rgos_exp)) {
smp_mb(); /* Ensure GP ends before subsequent accesses. */
return true;
}
return false;
}
EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu_full);
/**
* cond_synchronize_rcu - Conditionally wait for an RCU grace period
* @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited()
*
* If a full RCU grace period has elapsed since the earlier call to
* get_state_synchronize_rcu() or start_poll_synchronize_rcu(), just return.
* Otherwise, invoke synchronize_rcu() to wait for a full grace period.
*
* Yes, this function does not take counter wrap into account.
* But counter wrap is harmless. If the counter wraps, we have waited for
* more than 2 billion grace periods (and way more on a 64-bit system!),
* so waiting for a couple of additional grace periods should be just fine.
*
* This function provides the same memory-ordering guarantees that
* would be provided by a synchronize_rcu() that was invoked at the call
* to the function that provided @oldstate and that returned at the end
* of this function.
*/
void cond_synchronize_rcu(unsigned long oldstate)
{
if (!poll_state_synchronize_rcu(oldstate))
synchronize_rcu();
}
EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
/**
* cond_synchronize_rcu_full - Conditionally wait for an RCU grace period
* @rgosp: value from get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), or start_poll_synchronize_rcu_expedited_full()
*
* If a full RCU grace period has elapsed since the call to
* get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(),
* or start_poll_synchronize_rcu_expedited_full() from which @rgosp was
* obtained, just return. Otherwise, invoke synchronize_rcu() to wait
* for a full grace period.
*
* Yes, this function does not take counter wrap into account.
* But counter wrap is harmless. If the counter wraps, we have waited for
* more than 2 billion grace periods (and way more on a 64-bit system!),
* so waiting for a couple of additional grace periods should be just fine.
*
* This function provides the same memory-ordering guarantees that
* would be provided by a synchronize_rcu() that was invoked at the call
* to the function that provided @rgosp and that returned at the end of
* this function.
*/
void cond_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
{
if (!poll_state_synchronize_rcu_full(rgosp))
synchronize_rcu();
}
EXPORT_SYMBOL_GPL(cond_synchronize_rcu_full);
/*
* Check to see if there is any immediate RCU-related work to be done by
* the current CPU, returning 1 if so and zero otherwise. The checks are
* in order of increasing expense: checks that can be carried out against
* CPU-local state are performed first. However, we must check for CPU
* stalls first, else we might not get a chance.
*/
static int rcu_pending(int user)
{
bool gp_in_progress;
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
struct rcu_node *rnp = rdp->mynode;
lockdep_assert_irqs_disabled();
/* Check for CPU stalls, if enabled. */
check_cpu_stall(rdp);
/* Does this CPU need a deferred NOCB wakeup? */
if (rcu_nocb_need_deferred_wakeup(rdp, RCU_NOCB_WAKE))
return 1;
/* Is this a nohz_full CPU in userspace or idle? (Ignore RCU if so.) */
if ((user || rcu_is_cpu_rrupt_from_idle()) && rcu_nohz_full_cpu())
return 0;
/* Is the RCU core waiting for a quiescent state from this CPU? */
gp_in_progress = rcu_gp_in_progress();
if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm && gp_in_progress)
return 1;
/* Does this CPU have callbacks ready to invoke? */
if (!rcu_rdp_is_offloaded(rdp) &&
rcu_segcblist_ready_cbs(&rdp->cblist))
return 1;
/* Has RCU gone idle with this CPU needing another grace period? */
if (!gp_in_progress && rcu_segcblist_is_enabled(&rdp->cblist) &&
!rcu_rdp_is_offloaded(rdp) &&
!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
return 1;
/* Have RCU grace period completed or started? */
if (rcu_seq_current(&rnp->gp_seq) != rdp->gp_seq ||
unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */
return 1;
/* nothing to do */
return 0;
}
/*
* Helper function for rcu_barrier() tracing. If tracing is disabled,
* the compiler is expected to optimize this away.
*/
static void rcu_barrier_trace(const char *s, int cpu, unsigned long done)
{
trace_rcu_barrier(rcu_state.name, s, cpu,
atomic_read(&rcu_state.barrier_cpu_count), done);
}
/*
* RCU callback function for rcu_barrier(). If we are last, wake
* up the task executing rcu_barrier().
*
* Note that the value of rcu_state.barrier_sequence must be captured
* before the atomic_dec_and_test(). Otherwise, if this CPU is not last,
* other CPUs might count the value down to zero before this CPU gets
* around to invoking rcu_barrier_trace(), which might result in bogus
* data from the next instance of rcu_barrier().
*/
static void rcu_barrier_callback(struct rcu_head *rhp)
{
unsigned long __maybe_unused s = rcu_state.barrier_sequence;
if (atomic_dec_and_test(&rcu_state.barrier_cpu_count)) {
rcu_barrier_trace(TPS("LastCB"), -1, s);
complete(&rcu_state.barrier_completion);
} else {
rcu_barrier_trace(TPS("CB"), -1, s);
}
}
/*
* If needed, entrain an rcu_barrier() callback on rdp->cblist.
*/
static void rcu_barrier_entrain(struct rcu_data *rdp)
{
unsigned long gseq = READ_ONCE(rcu_state.barrier_sequence);
unsigned long lseq = READ_ONCE(rdp->barrier_seq_snap);
bool wake_nocb = false;
bool was_alldone = false;
lockdep_assert_held(&rcu_state.barrier_lock);
if (rcu_seq_state(lseq) || !rcu_seq_state(gseq) || rcu_seq_ctr(lseq) != rcu_seq_ctr(gseq))
return;
rcu_barrier_trace(TPS("IRQ"), -1, rcu_state.barrier_sequence);
rdp->barrier_head.func = rcu_barrier_callback;
debug_rcu_head_queue(&rdp->barrier_head);
rcu_nocb_lock(rdp);
/*
* Flush bypass and wakeup rcuog if we add callbacks to an empty regular
* queue. This way we don't wait for bypass timer that can reach seconds
* if it's fully lazy.
*/
was_alldone = rcu_rdp_is_offloaded(rdp) && !rcu_segcblist_pend_cbs(&rdp->cblist);
WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false));
wake_nocb = was_alldone && rcu_segcblist_pend_cbs(&rdp->cblist);
if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head)) {
atomic_inc(&rcu_state.barrier_cpu_count);
} else {
debug_rcu_head_unqueue(&rdp->barrier_head);
rcu_barrier_trace(TPS("IRQNQ"), -1, rcu_state.barrier_sequence);
}
rcu_nocb_unlock(rdp);
if (wake_nocb)
wake_nocb_gp(rdp, false);
smp_store_release(&rdp->barrier_seq_snap, gseq);
}
/*
* Called with preemption disabled, and from cross-cpu IRQ context.
*/
static void rcu_barrier_handler(void *cpu_in)
{
uintptr_t cpu = (uintptr_t)cpu_in;
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
lockdep_assert_irqs_disabled();
WARN_ON_ONCE(cpu != rdp->cpu);
WARN_ON_ONCE(cpu != smp_processor_id());
raw_spin_lock(&rcu_state.barrier_lock);
rcu_barrier_entrain(rdp);
raw_spin_unlock(&rcu_state.barrier_lock);
}
/**
* rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
*
* Note that this primitive does not necessarily wait for an RCU grace period
* to complete. For example, if there are no RCU callbacks queued anywhere
* in the system, then rcu_barrier() is within its rights to return
* immediately, without waiting for anything, much less an RCU grace period.
*/
void rcu_barrier(void)
{
uintptr_t cpu;
unsigned long flags;
unsigned long gseq;
struct rcu_data *rdp;
unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence);
rcu_barrier_trace(TPS("Begin"), -1, s);
/* Take mutex to serialize concurrent rcu_barrier() requests. */
mutex_lock(&rcu_state.barrier_mutex);
/* Did someone else do our work for us? */
if (rcu_seq_done(&rcu_state.barrier_sequence, s)) {
rcu_barrier_trace(TPS("EarlyExit"), -1, rcu_state.barrier_sequence);
smp_mb(); /* caller's subsequent code after above check. */
mutex_unlock(&rcu_state.barrier_mutex);
return;
}
/* Mark the start of the barrier operation. */
raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
rcu_seq_start(&rcu_state.barrier_sequence);
gseq = rcu_state.barrier_sequence;
rcu_barrier_trace(TPS("Inc1"), -1, rcu_state.barrier_sequence);
/*
* Initialize the count to two rather than to zero in order
* to avoid a too-soon return to zero in case of an immediate
* invocation of the just-enqueued callback (or preemption of
* this task). Exclude CPU-hotplug operations to ensure that no
* offline non-offloaded CPU has callbacks queued.
*/
init_completion(&rcu_state.barrier_completion);
atomic_set(&rcu_state.barrier_cpu_count, 2);
raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
/*
* Force each CPU with callbacks to register a new callback.
* When that callback is invoked, we will know that all of the
* corresponding CPU's preceding callbacks have been invoked.
*/
for_each_possible_cpu(cpu) {
rdp = per_cpu_ptr(&rcu_data, cpu);
retry:
if (smp_load_acquire(&rdp->barrier_seq_snap) == gseq)
continue;
raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
if (!rcu_segcblist_n_cbs(&rdp->cblist)) {
WRITE_ONCE(rdp->barrier_seq_snap, gseq);
raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
rcu_barrier_trace(TPS("NQ"), cpu, rcu_state.barrier_sequence);
continue;
}
if (!rcu_rdp_cpu_online(rdp)) {
rcu_barrier_entrain(rdp);
WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq);
raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
rcu_barrier_trace(TPS("OfflineNoCBQ"), cpu, rcu_state.barrier_sequence);
continue;
}
raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
if (smp_call_function_single(cpu, rcu_barrier_handler, (void *)cpu, 1)) {
schedule_timeout_uninterruptible(1);
goto retry;
}
WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq);
rcu_barrier_trace(TPS("OnlineQ"), cpu, rcu_state.barrier_sequence);
}
/*
* Now that we have an rcu_barrier_callback() callback on each
* CPU, and thus each counted, remove the initial count.
*/
if (atomic_sub_and_test(2, &rcu_state.barrier_cpu_count))
complete(&rcu_state.barrier_completion);
/* Wait for all rcu_barrier_callback() callbacks to be invoked. */
wait_for_completion(&rcu_state.barrier_completion);
/* Mark the end of the barrier operation. */
rcu_barrier_trace(TPS("Inc2"), -1, rcu_state.barrier_sequence);
rcu_seq_end(&rcu_state.barrier_sequence);
gseq = rcu_state.barrier_sequence;
for_each_possible_cpu(cpu) {
rdp = per_cpu_ptr(&rcu_data, cpu);
WRITE_ONCE(rdp->barrier_seq_snap, gseq);
}
/* Other rcu_barrier() invocations can now safely proceed. */
mutex_unlock(&rcu_state.barrier_mutex);
}
EXPORT_SYMBOL_GPL(rcu_barrier);
/*
* Compute the mask of online CPUs for the specified rcu_node structure.
* This will not be stable unless the rcu_node structure's ->lock is
* held, but the bit corresponding to the current CPU will be stable
* in most contexts.
*/
static unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
{
return READ_ONCE(rnp->qsmaskinitnext);
}
/*
* Is the CPU corresponding to the specified rcu_data structure online
* from RCU's perspective? This perspective is given by that structure's
* ->qsmaskinitnext field rather than by the global cpu_online_mask.
*/
static bool rcu_rdp_cpu_online(struct rcu_data *rdp)
{
return !!(rdp->grpmask & rcu_rnp_online_cpus(rdp->mynode));
}
#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
/*
* Is the current CPU online as far as RCU is concerned?
*
* Disable preemption to avoid false positives that could otherwise
* happen due to the current CPU number being sampled, this task being
* preempted, its old CPU being taken offline, resuming on some other CPU,
* then determining that its old CPU is now offline.
*
* Disable checking if in an NMI handler because we cannot safely
* report errors from NMI handlers anyway. In addition, it is OK to use
* RCU on an offline processor during initial boot, hence the check for
* rcu_scheduler_fully_active.
*/
bool rcu_lockdep_current_cpu_online(void)
{
struct rcu_data *rdp;
bool ret = false;
if (in_nmi() || !rcu_scheduler_fully_active)
return true;
preempt_disable_notrace();
rdp = this_cpu_ptr(&rcu_data);
/*
* Strictly, we care here about the case where the current CPU is
* in rcu_cpu_starting() and thus has an excuse for rdp->grpmask
* not being up to date. So arch_spin_is_locked() might have a
* false positive if it's held by some *other* CPU, but that's
* OK because that just means a false *negative* on the warning.
*/
if (rcu_rdp_cpu_online(rdp) || arch_spin_is_locked(&rcu_state.ofl_lock))
ret = true;
preempt_enable_notrace();
return ret;
}
EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
// Has rcu_init() been invoked? This is used (for example) to determine
// whether spinlocks may be acquired safely.
static bool rcu_init_invoked(void)
{
return !!rcu_state.n_online_cpus;
}
/*
* Near the end of the offline process. Trace the fact that this CPU
* is going offline.
*/
int rcutree_dying_cpu(unsigned int cpu)
{
bool blkd;
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
struct rcu_node *rnp = rdp->mynode;
if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
return 0;
blkd = !!(READ_ONCE(rnp->qsmask) & rdp->grpmask);
trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
blkd ? TPS("cpuofl-bgp") : TPS("cpuofl"));
return 0;
}
/*
* All CPUs for the specified rcu_node structure have gone offline,
* and all tasks that were preempted within an RCU read-side critical
* section while running on one of those CPUs have since exited their RCU
* read-side critical section. Some other CPU is reporting this fact with
* the specified rcu_node structure's ->lock held and interrupts disabled.
* This function therefore goes up the tree of rcu_node structures,
* clearing the corresponding bits in the ->qsmaskinit fields. Note that
* the leaf rcu_node structure's ->qsmaskinit field has already been
* updated.
*
* This function does check that the specified rcu_node structure has
* all CPUs offline and no blocked tasks, so it is OK to invoke it
* prematurely. That said, invoking it after the fact will cost you
* a needless lock acquisition. So once it has done its work, don't
* invoke it again.
*/
static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
{
long mask;
struct rcu_node *rnp = rnp_leaf;
raw_lockdep_assert_held_rcu_node(rnp_leaf);
if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
WARN_ON_ONCE(rnp_leaf->qsmaskinit) ||
WARN_ON_ONCE(rcu_preempt_has_tasks(rnp_leaf)))
return;
for (;;) {
mask = rnp->grpmask;
rnp = rnp->parent;
if (!rnp)
break;
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
rnp->qsmaskinit &= ~mask;
/* Between grace periods, so better already be zero! */
WARN_ON_ONCE(rnp->qsmask);
if (rnp->qsmaskinit) {
raw_spin_unlock_rcu_node(rnp);
/* irqs remain disabled. */
return;
}
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
}
}
/*
* The CPU has been completely removed, and some other CPU is reporting
* this fact from process context. Do the remainder of the cleanup.
* There can only be one CPU hotplug operation at a time, so no need for
* explicit locking.
*/
int rcutree_dead_cpu(unsigned int cpu)
{
if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
return 0;
WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1);
// Stop-machine done, so allow nohz_full to disable tick.
tick_dep_clear(TICK_DEP_BIT_RCU);
return 0;
}
/*
* Propagate ->qsinitmask bits up the rcu_node tree to account for the
* first CPU in a given leaf rcu_node structure coming online. The caller
* must hold the corresponding leaf rcu_node ->lock with interrupts
* disabled.
*/
static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
{
long mask;
long oldmask;
struct rcu_node *rnp = rnp_leaf;
raw_lockdep_assert_held_rcu_node(rnp_leaf);
WARN_ON_ONCE(rnp->wait_blkd_tasks);
for (;;) {
mask = rnp->grpmask;
rnp = rnp->parent;
if (rnp == NULL)
return;
raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
oldmask = rnp->qsmaskinit;
rnp->qsmaskinit |= mask;
raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
if (oldmask)
return;
}
}
/*
* Do boot-time initialization of a CPU's per-CPU RCU data.
*/
static void __init
rcu_boot_init_percpu_data(int cpu)
{
struct context_tracking *ct = this_cpu_ptr(&context_tracking);
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
/* Set up local state, ensuring consistent view of global state. */
rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
INIT_WORK(&rdp->strict_work, strict_work_handler);
WARN_ON_ONCE(ct->dynticks_nesting != 1);
WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu)));
rdp->barrier_seq_snap = rcu_state.barrier_sequence;
rdp->rcu_ofl_gp_seq = rcu_state.gp_seq;
rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED;
rdp->rcu_onl_gp_seq = rcu_state.gp_seq;
rdp->rcu_onl_gp_flags = RCU_GP_CLEANED;
rdp->last_sched_clock = jiffies;
rdp->cpu = cpu;
rcu_boot_init_nocb_percpu_data(rdp);
}
/*
* Invoked early in the CPU-online process, when pretty much all services
* are available. The incoming CPU is not present.
*
* Initializes a CPU's per-CPU RCU data. Note that only one online or
* offline event can be happening at a given time. Note also that we can
* accept some slop in the rsp->gp_seq access due to the fact that this
* CPU cannot possibly have any non-offloaded RCU callbacks in flight yet.
* And any offloaded callbacks are being numbered elsewhere.
*/
int rcutree_prepare_cpu(unsigned int cpu)
{
unsigned long flags;
struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
struct rcu_node *rnp = rcu_get_root();
/* Set up local state, ensuring consistent view of global state. */
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rdp->qlen_last_fqs_check = 0;
rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
rdp->blimit = blimit;
ct->dynticks_nesting = 1; /* CPU not up, no tearing. */
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
/*
* Only non-NOCB CPUs that didn't have early-boot callbacks need to be
* (re-)initialized.
*/
if (!rcu_segcblist_is_enabled(&rdp->cblist))
rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
/*
* Add CPU to leaf rcu_node pending-online bitmask. Any needed
* propagation up the rcu_node tree will happen at the beginning
* of the next grace period.
*/
rnp = rdp->mynode;
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
rdp->beenonline = true; /* We have now been online. */
rdp->gp_seq = READ_ONCE(rnp->gp_seq);
rdp->gp_seq_needed = rdp->gp_seq;
rdp->cpu_no_qs.b.norm = true;
rdp->core_needs_qs = false;
rdp->rcu_iw_pending = false;
rdp->rcu_iw = IRQ_WORK_INIT_HARD(rcu_iw_handler);
rdp->rcu_iw_gp_seq = rdp->gp_seq - 1;
trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl"));
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
rcu_spawn_one_boost_kthread(rnp);
rcu_spawn_cpu_nocb_kthread(cpu);
WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus + 1);
return 0;
}
/*
* Update RCU priority boot kthread affinity for CPU-hotplug changes.
*/
static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
{
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
}
/*
* Near the end of the CPU-online process. Pretty much all services
* enabled, and the CPU is now very much alive.
*/
int rcutree_online_cpu(unsigned int cpu)
{
unsigned long flags;
struct rcu_data *rdp;
struct rcu_node *rnp;
rdp = per_cpu_ptr(&rcu_data, cpu);
rnp = rdp->mynode;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rnp->ffmask |= rdp->grpmask;
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
return 0; /* Too early in boot for scheduler work. */
sync_sched_exp_online_cleanup(cpu);
rcutree_affinity_setting(cpu, -1);
// Stop-machine done, so allow nohz_full to disable tick.
tick_dep_clear(TICK_DEP_BIT_RCU);
return 0;
}
/*
* Near the beginning of the process. The CPU is still very much alive
* with pretty much all services enabled.
*/
int rcutree_offline_cpu(unsigned int cpu)
{
unsigned long flags;
struct rcu_data *rdp;
struct rcu_node *rnp;
rdp = per_cpu_ptr(&rcu_data, cpu);
rnp = rdp->mynode;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rnp->ffmask &= ~rdp->grpmask;
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
rcutree_affinity_setting(cpu, cpu);
// nohz_full CPUs need the tick for stop-machine to work quickly
tick_dep_set(TICK_DEP_BIT_RCU);
return 0;
}
/*
* Mark the specified CPU as being online so that subsequent grace periods
* (both expedited and normal) will wait on it. Note that this means that
* incoming CPUs are not allowed to use RCU read-side critical sections
* until this function is called. Failing to observe this restriction
* will result in lockdep splats.
*
* Note that this function is special in that it is invoked directly
* from the incoming CPU rather than from the cpuhp_step mechanism.
* This is because this function must be invoked at a precise location.
*/
void rcu_cpu_starting(unsigned int cpu)
{
unsigned long flags;
unsigned long mask;
struct rcu_data *rdp;
struct rcu_node *rnp;
bool newcpu;
rdp = per_cpu_ptr(&rcu_data, cpu);
if (rdp->cpu_started)
return;
rdp->cpu_started = true;
rnp = rdp->mynode;
mask = rdp->grpmask;
local_irq_save(flags);
arch_spin_lock(&rcu_state.ofl_lock);
rcu_dynticks_eqs_online();
raw_spin_lock(&rcu_state.barrier_lock);
raw_spin_lock_rcu_node(rnp);
WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask);
raw_spin_unlock(&rcu_state.barrier_lock);
newcpu = !(rnp->expmaskinitnext & mask);
rnp->expmaskinitnext |= mask;
/* Allow lockless access for expedited grace periods. */
smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + newcpu); /* ^^^ */
ASSERT_EXCLUSIVE_WRITER(rcu_state.ncpus);
rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */
rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq);
rdp->rcu_onl_gp_flags = READ_ONCE(rcu_state.gp_flags);
/* An incoming CPU should never be blocking a grace period. */
if (WARN_ON_ONCE(rnp->qsmask & mask)) { /* RCU waiting on incoming CPU? */
/* rcu_report_qs_rnp() *really* wants some flags to restore */
unsigned long flags2;
local_irq_save(flags2);
rcu_disable_urgency_upon_qs(rdp);
/* Report QS -after- changing ->qsmaskinitnext! */
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags2);
} else {
raw_spin_unlock_rcu_node(rnp);
}
arch_spin_unlock(&rcu_state.ofl_lock);
local_irq_restore(flags);
smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
}
/*
* The outgoing function has no further need of RCU, so remove it from
* the rcu_node tree's ->qsmaskinitnext bit masks.
*
* Note that this function is special in that it is invoked directly
* from the outgoing CPU rather than from the cpuhp_step mechanism.
* This is because this function must be invoked at a precise location.
*/
void rcu_report_dead(unsigned int cpu)
{
unsigned long flags, seq_flags;
unsigned long mask;
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
// Do any dangling deferred wakeups.
do_nocb_deferred_wakeup(rdp);
rcu_preempt_deferred_qs(current);
/* Remove outgoing CPU from mask in the leaf rcu_node structure. */
mask = rdp->grpmask;
local_irq_save(seq_flags);
arch_spin_lock(&rcu_state.ofl_lock);
raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
rdp->rcu_ofl_gp_seq = READ_ONCE(rcu_state.gp_seq);
rdp->rcu_ofl_gp_flags = READ_ONCE(rcu_state.gp_flags);
if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */
/* Report quiescent state -before- changing ->qsmaskinitnext! */
rcu_disable_urgency_upon_qs(rdp);
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
raw_spin_lock_irqsave_rcu_node(rnp, flags);
}
WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext & ~mask);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
arch_spin_unlock(&rcu_state.ofl_lock);
local_irq_restore(seq_flags);
rdp->cpu_started = false;
}
#ifdef CONFIG_HOTPLUG_CPU
/*
* The outgoing CPU has just passed through the dying-idle state, and we
* are being invoked from the CPU that was IPIed to continue the offline
* operation. Migrate the outgoing CPU's callbacks to the current CPU.
*/
void rcutree_migrate_callbacks(int cpu)
{
unsigned long flags;
struct rcu_data *my_rdp;
struct rcu_node *my_rnp;
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
bool needwake;
if (rcu_rdp_is_offloaded(rdp) ||
rcu_segcblist_empty(&rdp->cblist))
return; /* No callbacks to migrate. */
raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
WARN_ON_ONCE(rcu_rdp_cpu_online(rdp));
rcu_barrier_entrain(rdp);
my_rdp = this_cpu_ptr(&rcu_data);
my_rnp = my_rdp->mynode;
rcu_nocb_lock(my_rdp); /* irqs already disabled. */
WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies, false));
raw_spin_lock_rcu_node(my_rnp); /* irqs already disabled. */
/* Leverage recent GPs and set GP for new callbacks. */
needwake = rcu_advance_cbs(my_rnp, rdp) ||
rcu_advance_cbs(my_rnp, my_rdp);
rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);
raw_spin_unlock(&rcu_state.barrier_lock); /* irqs remain disabled. */
needwake = needwake || rcu_advance_cbs(my_rnp, my_rdp);
rcu_segcblist_disable(&rdp->cblist);
WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != !rcu_segcblist_n_cbs(&my_rdp->cblist));
check_cb_ovld_locked(my_rdp, my_rnp);
if (rcu_rdp_is_offloaded(my_rdp)) {
raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */
__call_rcu_nocb_wake(my_rdp, true, flags);
} else {
rcu_nocb_unlock(my_rdp); /* irqs remain disabled. */
raw_spin_unlock_irqrestore_rcu_node(my_rnp, flags);
}
if (needwake)
rcu_gp_kthread_wake();
lockdep_assert_irqs_enabled();
WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
!rcu_segcblist_empty(&rdp->cblist),
"rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
cpu, rcu_segcblist_n_cbs(&rdp->cblist),
rcu_segcblist_first_cb(&rdp->cblist));
}
#endif
/*
* On non-huge systems, use expedited RCU grace periods to make suspend
* and hibernation run faster.
*/
static int rcu_pm_notify(struct notifier_block *self,
unsigned long action, void *hcpu)
{
switch (action) {
case PM_HIBERNATION_PREPARE:
case PM_SUSPEND_PREPARE:
rcu_async_hurry();
rcu_expedite_gp();
break;
case PM_POST_HIBERNATION:
case PM_POST_SUSPEND:
rcu_unexpedite_gp();
rcu_async_relax();
break;
default:
break;
}
return NOTIFY_OK;
}
#ifdef CONFIG_RCU_EXP_KTHREAD
struct kthread_worker *rcu_exp_gp_kworker;
struct kthread_worker *rcu_exp_par_gp_kworker;
static void __init rcu_start_exp_gp_kworkers(void)
{
const char *par_gp_kworker_name = "rcu_exp_par_gp_kthread_worker";
const char *gp_kworker_name = "rcu_exp_gp_kthread_worker";
struct sched_param param = { .sched_priority = kthread_prio };
rcu_exp_gp_kworker = kthread_create_worker(0, gp_kworker_name);
if (IS_ERR_OR_NULL(rcu_exp_gp_kworker)) {
pr_err("Failed to create %s!\n", gp_kworker_name);
return;
}
rcu_exp_par_gp_kworker = kthread_create_worker(0, par_gp_kworker_name);
if (IS_ERR_OR_NULL(rcu_exp_par_gp_kworker)) {
pr_err("Failed to create %s!\n", par_gp_kworker_name);
kthread_destroy_worker(rcu_exp_gp_kworker);
return;
}
sched_setscheduler_nocheck(rcu_exp_gp_kworker->task, SCHED_FIFO, &param);
sched_setscheduler_nocheck(rcu_exp_par_gp_kworker->task, SCHED_FIFO,
&param);
}
static inline void rcu_alloc_par_gp_wq(void)
{
}
#else /* !CONFIG_RCU_EXP_KTHREAD */
struct workqueue_struct *rcu_par_gp_wq;
static void __init rcu_start_exp_gp_kworkers(void)
{
}
static inline void rcu_alloc_par_gp_wq(void)
{
rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0);
WARN_ON(!rcu_par_gp_wq);
}
#endif /* CONFIG_RCU_EXP_KTHREAD */
/*
* Spawn the kthreads that handle RCU's grace periods.
*/
static int __init rcu_spawn_gp_kthread(void)
{
unsigned long flags;
struct rcu_node *rnp;
struct sched_param sp;
struct task_struct *t;
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
rcu_scheduler_fully_active = 1;
t = kthread_create(rcu_gp_kthread, NULL, "%s", rcu_state.name);
if (WARN_ONCE(IS_ERR(t), "%s: Could not start grace-period kthread, OOM is now expected behavior\n", __func__))
return 0;
if (kthread_prio) {
sp.sched_priority = kthread_prio;
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
}
rnp = rcu_get_root();
raw_spin_lock_irqsave_rcu_node(rnp, flags);
WRITE_ONCE(rcu_state.gp_activity, jiffies);
WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
// Reset .gp_activity and .gp_req_activity before setting .gp_kthread.
smp_store_release(&rcu_state.gp_kthread, t); /* ^^^ */
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
wake_up_process(t);
/* This is a pre-SMP initcall, we expect a single CPU */
WARN_ON(num_online_cpus() > 1);
/*
* Those kthreads couldn't be created on rcu_init() -> rcutree_prepare_cpu()
* due to rcu_scheduler_fully_active.
*/
rcu_spawn_cpu_nocb_kthread(smp_processor_id());
rcu_spawn_one_boost_kthread(rdp->mynode);
rcu_spawn_core_kthreads();
/* Create kthread worker for expedited GPs */
rcu_start_exp_gp_kworkers();
return 0;
}
early_initcall(rcu_spawn_gp_kthread);
/*
* This function is invoked towards the end of the scheduler's
* initialization process. Before this is called, the idle task might
* contain synchronous grace-period primitives (during which time, this idle
* task is booting the system, and such primitives are no-ops). After this
* function is called, any synchronous grace-period primitives are run as
* expedited, with the requesting task driving the grace period forward.
* A later core_initcall() rcu_set_runtime_mode() will switch to full
* runtime RCU functionality.
*/
void rcu_scheduler_starting(void)
{
unsigned long flags;
struct rcu_node *rnp;
WARN_ON(num_online_cpus() != 1);
WARN_ON(nr_context_switches() > 0);
rcu_test_sync_prims();
// Fix up the ->gp_seq counters.
local_irq_save(flags);
rcu_for_each_node_breadth_first(rnp)
rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq;
local_irq_restore(flags);
// Switch out of early boot mode.
rcu_scheduler_active = RCU_SCHEDULER_INIT;
rcu_test_sync_prims();
}
/*
* Helper function for rcu_init() that initializes the rcu_state structure.
*/
static void __init rcu_init_one(void)
{
static const char * const buf[] = RCU_NODE_NAME_INIT;
static const char * const fqs[] = RCU_FQS_NAME_INIT;
static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
int levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */
int cpustride = 1;
int i;
int j;
struct rcu_node *rnp;
BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
/* Silence gcc 4.8 false positive about array index out of range. */
if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
panic("rcu_init_one: rcu_num_lvls out of range");
/* Initialize the level-tracking arrays. */
for (i = 1; i < rcu_num_lvls; i++)
rcu_state.level[i] =
rcu_state.level[i - 1] + num_rcu_lvl[i - 1];
rcu_init_levelspread(levelspread, num_rcu_lvl);
/* Initialize the elements themselves, starting from the leaves. */
for (i = rcu_num_lvls - 1; i >= 0; i--) {
cpustride *= levelspread[i];
rnp = rcu_state.level[i];
for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) {
raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
&rcu_node_class[i], buf[i]);
raw_spin_lock_init(&rnp->fqslock);
lockdep_set_class_and_name(&rnp->fqslock,
&rcu_fqs_class[i], fqs[i]);
rnp->gp_seq = rcu_state.gp_seq;
rnp->gp_seq_needed = rcu_state.gp_seq;
rnp->completedqs = rcu_state.gp_seq;
rnp->qsmask = 0;
rnp->qsmaskinit = 0;
rnp->grplo = j * cpustride;
rnp->grphi = (j + 1) * cpustride - 1;
if (rnp->grphi >= nr_cpu_ids)
rnp->grphi = nr_cpu_ids - 1;
if (i == 0) {
rnp->grpnum = 0;
rnp->grpmask = 0;
rnp->parent = NULL;
} else {
rnp->grpnum = j % levelspread[i - 1];
rnp->grpmask = BIT(rnp->grpnum);
rnp->parent = rcu_state.level[i - 1] +
j / levelspread[i - 1];
}
rnp->level = i;
INIT_LIST_HEAD(&rnp->blkd_tasks);
rcu_init_one_nocb(rnp);
init_waitqueue_head(&rnp->exp_wq[0]);
init_waitqueue_head(&rnp->exp_wq[1]);
init_waitqueue_head(&rnp->exp_wq[2]);
init_waitqueue_head(&rnp->exp_wq[3]);
spin_lock_init(&rnp->exp_lock);
mutex_init(&rnp->boost_kthread_mutex);
raw_spin_lock_init(&rnp->exp_poll_lock);
rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
INIT_WORK(&rnp->exp_poll_wq, sync_rcu_do_polled_gp);
}
}
init_swait_queue_head(&rcu_state.gp_wq);
init_swait_queue_head(&rcu_state.expedited_wq);
rnp = rcu_first_leaf_node();
for_each_possible_cpu(i) {
while (i > rnp->grphi)
rnp++;
per_cpu_ptr(&rcu_data, i)->mynode = rnp;
rcu_boot_init_percpu_data(i);
}
}
/*
* Force priority from the kernel command-line into range.
*/
static void __init sanitize_kthread_prio(void)
{
int kthread_prio_in = kthread_prio;
if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 2
&& IS_BUILTIN(CONFIG_RCU_TORTURE_TEST))
kthread_prio = 2;
else if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
kthread_prio = 1;
else if (kthread_prio < 0)
kthread_prio = 0;
else if (kthread_prio > 99)
kthread_prio = 99;
if (kthread_prio != kthread_prio_in)
pr_alert("%s: Limited prio to %d from %d\n",
__func__, kthread_prio, kthread_prio_in);
}
/*
* Compute the rcu_node tree geometry from kernel parameters. This cannot
* replace the definitions in tree.h because those are needed to size
* the ->node array in the rcu_state structure.
*/
void rcu_init_geometry(void)
{
ulong d;
int i;
static unsigned long old_nr_cpu_ids;
int rcu_capacity[RCU_NUM_LVLS];
static bool initialized;
if (initialized) {
/*
* Warn if setup_nr_cpu_ids() had not yet been invoked,
* unless nr_cpus_ids == NR_CPUS, in which case who cares?
*/
WARN_ON_ONCE(old_nr_cpu_ids != nr_cpu_ids);
return;
}
old_nr_cpu_ids = nr_cpu_ids;
initialized = true;
/*
* Initialize any unspecified boot parameters.
* The default values of jiffies_till_first_fqs and
* jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
* value, which is a function of HZ, then adding one for each
* RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
*/
d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
if (jiffies_till_first_fqs == ULONG_MAX)
jiffies_till_first_fqs = d;
if (jiffies_till_next_fqs == ULONG_MAX)
jiffies_till_next_fqs = d;
adjust_jiffies_till_sched_qs();
/* If the compile-time values are accurate, just leave. */
if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
nr_cpu_ids == NR_CPUS)
return;
pr_info("Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%u\n",
rcu_fanout_leaf, nr_cpu_ids);
/*
* The boot-time rcu_fanout_leaf parameter must be at least two
* and cannot exceed the number of bits in the rcu_node masks.
* Complain and fall back to the compile-time values if this
* limit is exceeded.
*/
if (rcu_fanout_leaf < 2 ||
rcu_fanout_leaf > sizeof(unsigned long) * 8) {
rcu_fanout_leaf = RCU_FANOUT_LEAF;
WARN_ON(1);
return;
}
/*
* Compute number of nodes that can be handled an rcu_node tree
* with the given number of levels.
*/
rcu_capacity[0] = rcu_fanout_leaf;
for (i = 1; i < RCU_NUM_LVLS; i++)
rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
/*
* The tree must be able to accommodate the configured number of CPUs.
* If this limit is exceeded, fall back to the compile-time values.
*/
if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
rcu_fanout_leaf = RCU_FANOUT_LEAF;
WARN_ON(1);
return;
}
/* Calculate the number of levels in the tree. */
for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
}
rcu_num_lvls = i + 1;
/* Calculate the number of rcu_nodes at each level of the tree. */
for (i = 0; i < rcu_num_lvls; i++) {
int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
}
/* Calculate the total number of rcu_node structures. */
rcu_num_nodes = 0;
for (i = 0; i < rcu_num_lvls; i++)
rcu_num_nodes += num_rcu_lvl[i];
}
/*
* Dump out the structure of the rcu_node combining tree associated
* with the rcu_state structure.
*/
static void __init rcu_dump_rcu_node_tree(void)
{
int level = 0;
struct rcu_node *rnp;
pr_info("rcu_node tree layout dump\n");
pr_info(" ");
rcu_for_each_node_breadth_first(rnp) {
if (rnp->level != level) {
pr_cont("\n");
pr_info(" ");
level = rnp->level;
}
pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum);
}
pr_cont("\n");
}
struct workqueue_struct *rcu_gp_wq;
static void __init kfree_rcu_batch_init(void)
{
int cpu;
int i, j;
/* Clamp it to [0:100] seconds interval. */
if (rcu_delay_page_cache_fill_msec < 0 ||
rcu_delay_page_cache_fill_msec > 100 * MSEC_PER_SEC) {
rcu_delay_page_cache_fill_msec =
clamp(rcu_delay_page_cache_fill_msec, 0,
(int) (100 * MSEC_PER_SEC));
pr_info("Adjusting rcutree.rcu_delay_page_cache_fill_msec to %d ms.\n",
rcu_delay_page_cache_fill_msec);
}
for_each_possible_cpu(cpu) {
struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
for (i = 0; i < KFREE_N_BATCHES; i++) {
INIT_RCU_WORK(&krcp->krw_arr[i].rcu_work, kfree_rcu_work);
krcp->krw_arr[i].krcp = krcp;
for (j = 0; j < FREE_N_CHANNELS; j++)
INIT_LIST_HEAD(&krcp->krw_arr[i].bulk_head_free[j]);
}
for (i = 0; i < FREE_N_CHANNELS; i++)
INIT_LIST_HEAD(&krcp->bulk_head[i]);
INIT_DELAYED_WORK(&krcp->monitor_work, kfree_rcu_monitor);
INIT_DELAYED_WORK(&krcp->page_cache_work, fill_page_cache_func);
krcp->initialized = true;
}
if (register_shrinker(&kfree_rcu_shrinker, "rcu-kfree"))
pr_err("Failed to register kfree_rcu() shrinker!\n");
}
void __init rcu_init(void)
{
int cpu = smp_processor_id();
rcu_early_boot_tests();
kfree_rcu_batch_init();
rcu_bootup_announce();
sanitize_kthread_prio();
rcu_init_geometry();
rcu_init_one();
if (dump_tree)
rcu_dump_rcu_node_tree();
if (use_softirq)
open_softirq(RCU_SOFTIRQ, rcu_core_si);
/*
* We don't need protection against CPU-hotplug here because
* this is called early in boot, before either interrupts
* or the scheduler are operational.
*/
pm_notifier(rcu_pm_notify, 0);
WARN_ON(num_online_cpus() > 1); // Only one CPU this early in boot.
rcutree_prepare_cpu(cpu);
rcu_cpu_starting(cpu);
rcutree_online_cpu(cpu);
/* Create workqueue for Tree SRCU and for expedited GPs. */
rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
WARN_ON(!rcu_gp_wq);
rcu_alloc_par_gp_wq();
/* Fill in default value for rcutree.qovld boot parameter. */
/* -After- the rcu_node ->lock fields are initialized! */
if (qovld < 0)
qovld_calc = DEFAULT_RCU_QOVLD_MULT * qhimark;
else
qovld_calc = qovld;
// Kick-start any polled grace periods that started early.
if (!(per_cpu_ptr(&rcu_data, cpu)->mynode->exp_seq_poll_rq & 0x1))
(void)start_poll_synchronize_rcu_expedited();
rcu_test_sync_prims();
}
#include "tree_stall.h"
#include "tree_exp.h"
#include "tree_nocb.h"
#include "tree_plugin.h"