288 lines
9.5 KiB
C
288 lines
9.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
|
|
#ifndef _LINUX_SWAIT_H
|
|
#define _LINUX_SWAIT_H
|
|
|
|
#include <linux/list.h>
|
|
#include <linux/stddef.h>
|
|
#include <linux/spinlock.h>
|
|
#include <linux/wait.h>
|
|
#include <asm/current.h>
|
|
|
|
/*
|
|
* Simple waitqueues are semantically very different to regular wait queues
|
|
* (wait.h). The most important difference is that the simple waitqueue allows
|
|
* for deterministic behaviour -- IOW it has strictly bounded IRQ and lock hold
|
|
* times.
|
|
*
|
|
* Mainly, this is accomplished by two things. Firstly not allowing swake_up_all
|
|
* from IRQ disabled, and dropping the lock upon every wakeup, giving a higher
|
|
* priority task a chance to run.
|
|
*
|
|
* Secondly, we had to drop a fair number of features of the other waitqueue
|
|
* code; notably:
|
|
*
|
|
* - mixing INTERRUPTIBLE and UNINTERRUPTIBLE sleeps on the same waitqueue;
|
|
* all wakeups are TASK_NORMAL in order to avoid O(n) lookups for the right
|
|
* sleeper state.
|
|
*
|
|
* - the !exclusive mode; because that leads to O(n) wakeups, everything is
|
|
* exclusive. As such swake_up_one will only ever awake _one_ waiter.
|
|
*
|
|
* - custom wake callback functions; because you cannot give any guarantees
|
|
* about random code. This also allows swait to be used in RT, such that
|
|
* raw spinlock can be used for the swait queue head.
|
|
*
|
|
* As a side effect of these; the data structures are slimmer albeit more ad-hoc.
|
|
* For all the above, note that simple wait queues should _only_ be used under
|
|
* very specific realtime constraints -- it is best to stick with the regular
|
|
* wait queues in most cases.
|
|
*/
|
|
|
|
struct task_struct;
|
|
|
|
struct swait_queue_head {
|
|
raw_spinlock_t lock;
|
|
struct list_head task_list;
|
|
};
|
|
|
|
struct swait_queue {
|
|
struct task_struct *task;
|
|
struct list_head task_list;
|
|
};
|
|
|
|
#define __SWAITQUEUE_INITIALIZER(name) { \
|
|
.task = current, \
|
|
.task_list = LIST_HEAD_INIT((name).task_list), \
|
|
}
|
|
|
|
#define DECLARE_SWAITQUEUE(name) \
|
|
struct swait_queue name = __SWAITQUEUE_INITIALIZER(name)
|
|
|
|
#define __SWAIT_QUEUE_HEAD_INITIALIZER(name) { \
|
|
.lock = __RAW_SPIN_LOCK_UNLOCKED(name.lock), \
|
|
.task_list = LIST_HEAD_INIT((name).task_list), \
|
|
}
|
|
|
|
#define DECLARE_SWAIT_QUEUE_HEAD(name) \
|
|
struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INITIALIZER(name)
|
|
|
|
extern void __init_swait_queue_head(struct swait_queue_head *q, const char *name,
|
|
struct lock_class_key *key);
|
|
|
|
#define init_swait_queue_head(q) \
|
|
do { \
|
|
static struct lock_class_key __key; \
|
|
__init_swait_queue_head((q), #q, &__key); \
|
|
} while (0)
|
|
|
|
#ifdef CONFIG_LOCKDEP
|
|
# define __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name) \
|
|
({ init_swait_queue_head(&name); name; })
|
|
# define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name) \
|
|
struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name)
|
|
#else
|
|
# define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name) \
|
|
DECLARE_SWAIT_QUEUE_HEAD(name)
|
|
#endif
|
|
|
|
/**
|
|
* swait_active -- locklessly test for waiters on the queue
|
|
* @wq: the waitqueue to test for waiters
|
|
*
|
|
* returns true if the wait list is not empty
|
|
*
|
|
* NOTE: this function is lockless and requires care, incorrect usage _will_
|
|
* lead to sporadic and non-obvious failure.
|
|
*
|
|
* NOTE2: this function has the same above implications as regular waitqueues.
|
|
*
|
|
* Use either while holding swait_queue_head::lock or when used for wakeups
|
|
* with an extra smp_mb() like:
|
|
*
|
|
* CPU0 - waker CPU1 - waiter
|
|
*
|
|
* for (;;) {
|
|
* @cond = true; prepare_to_swait_exclusive(&wq_head, &wait, state);
|
|
* smp_mb(); // smp_mb() from set_current_state()
|
|
* if (swait_active(wq_head)) if (@cond)
|
|
* wake_up(wq_head); break;
|
|
* schedule();
|
|
* }
|
|
* finish_swait(&wq_head, &wait);
|
|
*
|
|
* Because without the explicit smp_mb() it's possible for the
|
|
* swait_active() load to get hoisted over the @cond store such that we'll
|
|
* observe an empty wait list while the waiter might not observe @cond.
|
|
* This, in turn, can trigger missing wakeups.
|
|
*
|
|
* Also note that this 'optimization' trades a spin_lock() for an smp_mb(),
|
|
* which (when the lock is uncontended) are of roughly equal cost.
|
|
*/
|
|
static inline int swait_active(struct swait_queue_head *wq)
|
|
{
|
|
return !list_empty(&wq->task_list);
|
|
}
|
|
|
|
/**
|
|
* swq_has_sleeper - check if there are any waiting processes
|
|
* @wq: the waitqueue to test for waiters
|
|
*
|
|
* Returns true if @wq has waiting processes
|
|
*
|
|
* Please refer to the comment for swait_active.
|
|
*/
|
|
static inline bool swq_has_sleeper(struct swait_queue_head *wq)
|
|
{
|
|
/*
|
|
* We need to be sure we are in sync with the list_add()
|
|
* modifications to the wait queue (task_list).
|
|
*
|
|
* This memory barrier should be paired with one on the
|
|
* waiting side.
|
|
*/
|
|
smp_mb();
|
|
return swait_active(wq);
|
|
}
|
|
|
|
extern void swake_up_one(struct swait_queue_head *q);
|
|
extern void swake_up_all(struct swait_queue_head *q);
|
|
extern void swake_up_locked(struct swait_queue_head *q);
|
|
|
|
extern void prepare_to_swait_exclusive(struct swait_queue_head *q, struct swait_queue *wait, int state);
|
|
extern long prepare_to_swait_event(struct swait_queue_head *q, struct swait_queue *wait, int state);
|
|
|
|
extern void __finish_swait(struct swait_queue_head *q, struct swait_queue *wait);
|
|
extern void finish_swait(struct swait_queue_head *q, struct swait_queue *wait);
|
|
|
|
/* as per ___wait_event() but for swait, therefore "exclusive == 1" */
|
|
#define ___swait_event(wq, condition, state, ret, cmd) \
|
|
({ \
|
|
__label__ __out; \
|
|
struct swait_queue __wait; \
|
|
long __ret = ret; \
|
|
\
|
|
INIT_LIST_HEAD(&__wait.task_list); \
|
|
for (;;) { \
|
|
long __int = prepare_to_swait_event(&wq, &__wait, state);\
|
|
\
|
|
if (condition) \
|
|
break; \
|
|
\
|
|
if (___wait_is_interruptible(state) && __int) { \
|
|
__ret = __int; \
|
|
goto __out; \
|
|
} \
|
|
\
|
|
cmd; \
|
|
} \
|
|
finish_swait(&wq, &__wait); \
|
|
__out: __ret; \
|
|
})
|
|
|
|
#define __swait_event(wq, condition) \
|
|
(void)___swait_event(wq, condition, TASK_UNINTERRUPTIBLE, 0, \
|
|
schedule())
|
|
|
|
#define swait_event_exclusive(wq, condition) \
|
|
do { \
|
|
if (condition) \
|
|
break; \
|
|
__swait_event(wq, condition); \
|
|
} while (0)
|
|
|
|
#define __swait_event_timeout(wq, condition, timeout) \
|
|
___swait_event(wq, ___wait_cond_timeout(condition), \
|
|
TASK_UNINTERRUPTIBLE, timeout, \
|
|
__ret = schedule_timeout(__ret))
|
|
|
|
#define swait_event_timeout_exclusive(wq, condition, timeout) \
|
|
({ \
|
|
long __ret = timeout; \
|
|
if (!___wait_cond_timeout(condition)) \
|
|
__ret = __swait_event_timeout(wq, condition, timeout); \
|
|
__ret; \
|
|
})
|
|
|
|
#define __swait_event_interruptible(wq, condition) \
|
|
___swait_event(wq, condition, TASK_INTERRUPTIBLE, 0, \
|
|
schedule())
|
|
|
|
#define swait_event_interruptible_exclusive(wq, condition) \
|
|
({ \
|
|
int __ret = 0; \
|
|
if (!(condition)) \
|
|
__ret = __swait_event_interruptible(wq, condition); \
|
|
__ret; \
|
|
})
|
|
|
|
#define __swait_event_interruptible_timeout(wq, condition, timeout) \
|
|
___swait_event(wq, ___wait_cond_timeout(condition), \
|
|
TASK_INTERRUPTIBLE, timeout, \
|
|
__ret = schedule_timeout(__ret))
|
|
|
|
#define swait_event_interruptible_timeout_exclusive(wq, condition, timeout)\
|
|
({ \
|
|
long __ret = timeout; \
|
|
if (!___wait_cond_timeout(condition)) \
|
|
__ret = __swait_event_interruptible_timeout(wq, \
|
|
condition, timeout); \
|
|
__ret; \
|
|
})
|
|
|
|
#define __swait_event_idle(wq, condition) \
|
|
(void)___swait_event(wq, condition, TASK_IDLE, 0, schedule())
|
|
|
|
/**
|
|
* swait_event_idle_exclusive - wait without system load contribution
|
|
* @wq: the waitqueue to wait on
|
|
* @condition: a C expression for the event to wait for
|
|
*
|
|
* The process is put to sleep (TASK_IDLE) until the @condition evaluates to
|
|
* true. The @condition is checked each time the waitqueue @wq is woken up.
|
|
*
|
|
* This function is mostly used when a kthread or workqueue waits for some
|
|
* condition and doesn't want to contribute to system load. Signals are
|
|
* ignored.
|
|
*/
|
|
#define swait_event_idle_exclusive(wq, condition) \
|
|
do { \
|
|
if (condition) \
|
|
break; \
|
|
__swait_event_idle(wq, condition); \
|
|
} while (0)
|
|
|
|
#define __swait_event_idle_timeout(wq, condition, timeout) \
|
|
___swait_event(wq, ___wait_cond_timeout(condition), \
|
|
TASK_IDLE, timeout, \
|
|
__ret = schedule_timeout(__ret))
|
|
|
|
/**
|
|
* swait_event_idle_timeout_exclusive - wait up to timeout without load contribution
|
|
* @wq: the waitqueue to wait on
|
|
* @condition: a C expression for the event to wait for
|
|
* @timeout: timeout at which we'll give up in jiffies
|
|
*
|
|
* The process is put to sleep (TASK_IDLE) until the @condition evaluates to
|
|
* true. The @condition is checked each time the waitqueue @wq is woken up.
|
|
*
|
|
* This function is mostly used when a kthread or workqueue waits for some
|
|
* condition and doesn't want to contribute to system load. Signals are
|
|
* ignored.
|
|
*
|
|
* Returns:
|
|
* 0 if the @condition evaluated to %false after the @timeout elapsed,
|
|
* 1 if the @condition evaluated to %true after the @timeout elapsed,
|
|
* or the remaining jiffies (at least 1) if the @condition evaluated
|
|
* to %true before the @timeout elapsed.
|
|
*/
|
|
#define swait_event_idle_timeout_exclusive(wq, condition, timeout) \
|
|
({ \
|
|
long __ret = timeout; \
|
|
if (!___wait_cond_timeout(condition)) \
|
|
__ret = __swait_event_idle_timeout(wq, \
|
|
condition, timeout); \
|
|
__ret; \
|
|
})
|
|
|
|
#endif /* _LINUX_SWAIT_H */
|