406 lines
10 KiB
C
406 lines
10 KiB
C
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// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2008 Oracle. All rights reserved.
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*/
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#include <linux/sched.h>
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#include <linux/pagemap.h>
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#include <linux/spinlock.h>
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#include <linux/page-flags.h>
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#include <asm/bug.h>
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#include "misc.h"
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#include "ctree.h"
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#include "extent_io.h"
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#include "locking.h"
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#include "accessors.h"
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/*
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* Lockdep class keys for extent_buffer->lock's in this root. For a given
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* eb, the lockdep key is determined by the btrfs_root it belongs to and
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* the level the eb occupies in the tree.
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*
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* Different roots are used for different purposes and may nest inside each
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* other and they require separate keysets. As lockdep keys should be
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* static, assign keysets according to the purpose of the root as indicated
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* by btrfs_root->root_key.objectid. This ensures that all special purpose
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* roots have separate keysets.
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*
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* Lock-nesting across peer nodes is always done with the immediate parent
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* node locked thus preventing deadlock. As lockdep doesn't know this, use
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* subclass to avoid triggering lockdep warning in such cases.
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*
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* The key is set by the readpage_end_io_hook after the buffer has passed
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* csum validation but before the pages are unlocked. It is also set by
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* btrfs_init_new_buffer on freshly allocated blocks.
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*
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* We also add a check to make sure the highest level of the tree is the
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* same as our lockdep setup here. If BTRFS_MAX_LEVEL changes, this code
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* needs update as well.
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*/
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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#if BTRFS_MAX_LEVEL != 8
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#error
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#endif
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#define DEFINE_LEVEL(stem, level) \
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.names[level] = "btrfs-" stem "-0" #level,
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#define DEFINE_NAME(stem) \
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DEFINE_LEVEL(stem, 0) \
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DEFINE_LEVEL(stem, 1) \
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DEFINE_LEVEL(stem, 2) \
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DEFINE_LEVEL(stem, 3) \
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DEFINE_LEVEL(stem, 4) \
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DEFINE_LEVEL(stem, 5) \
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DEFINE_LEVEL(stem, 6) \
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DEFINE_LEVEL(stem, 7)
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static struct btrfs_lockdep_keyset {
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u64 id; /* root objectid */
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/* Longest entry: btrfs-free-space-00 */
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char names[BTRFS_MAX_LEVEL][20];
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struct lock_class_key keys[BTRFS_MAX_LEVEL];
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} btrfs_lockdep_keysets[] = {
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{ .id = BTRFS_ROOT_TREE_OBJECTID, DEFINE_NAME("root") },
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{ .id = BTRFS_EXTENT_TREE_OBJECTID, DEFINE_NAME("extent") },
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{ .id = BTRFS_CHUNK_TREE_OBJECTID, DEFINE_NAME("chunk") },
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{ .id = BTRFS_DEV_TREE_OBJECTID, DEFINE_NAME("dev") },
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{ .id = BTRFS_CSUM_TREE_OBJECTID, DEFINE_NAME("csum") },
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{ .id = BTRFS_QUOTA_TREE_OBJECTID, DEFINE_NAME("quota") },
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{ .id = BTRFS_TREE_LOG_OBJECTID, DEFINE_NAME("log") },
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{ .id = BTRFS_TREE_RELOC_OBJECTID, DEFINE_NAME("treloc") },
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{ .id = BTRFS_DATA_RELOC_TREE_OBJECTID, DEFINE_NAME("dreloc") },
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{ .id = BTRFS_UUID_TREE_OBJECTID, DEFINE_NAME("uuid") },
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{ .id = BTRFS_FREE_SPACE_TREE_OBJECTID, DEFINE_NAME("free-space") },
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{ .id = 0, DEFINE_NAME("tree") },
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};
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#undef DEFINE_LEVEL
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#undef DEFINE_NAME
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void btrfs_set_buffer_lockdep_class(u64 objectid, struct extent_buffer *eb, int level)
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{
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struct btrfs_lockdep_keyset *ks;
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BUG_ON(level >= ARRAY_SIZE(ks->keys));
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/* Find the matching keyset, id 0 is the default entry */
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for (ks = btrfs_lockdep_keysets; ks->id; ks++)
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if (ks->id == objectid)
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break;
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lockdep_set_class_and_name(&eb->lock, &ks->keys[level], ks->names[level]);
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}
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void btrfs_maybe_reset_lockdep_class(struct btrfs_root *root, struct extent_buffer *eb)
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{
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if (test_bit(BTRFS_ROOT_RESET_LOCKDEP_CLASS, &root->state))
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btrfs_set_buffer_lockdep_class(root->root_key.objectid,
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eb, btrfs_header_level(eb));
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}
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#endif
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/*
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* Extent buffer locking
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* =====================
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*
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* We use a rw_semaphore for tree locking, and the semantics are exactly the
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* same:
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*
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* - reader/writer exclusion
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* - writer/writer exclusion
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* - reader/reader sharing
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* - try-lock semantics for readers and writers
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*
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* The rwsem implementation does opportunistic spinning which reduces number of
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* times the locking task needs to sleep.
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*/
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/*
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* __btrfs_tree_read_lock - lock extent buffer for read
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* @eb: the eb to be locked
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* @nest: the nesting level to be used for lockdep
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*
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* This takes the read lock on the extent buffer, using the specified nesting
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* level for lockdep purposes.
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*/
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void __btrfs_tree_read_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest)
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{
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u64 start_ns = 0;
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if (trace_btrfs_tree_read_lock_enabled())
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start_ns = ktime_get_ns();
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down_read_nested(&eb->lock, nest);
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trace_btrfs_tree_read_lock(eb, start_ns);
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}
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void btrfs_tree_read_lock(struct extent_buffer *eb)
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{
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__btrfs_tree_read_lock(eb, BTRFS_NESTING_NORMAL);
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}
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/*
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* Try-lock for read.
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*
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* Return 1 if the rwlock has been taken, 0 otherwise
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*/
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int btrfs_try_tree_read_lock(struct extent_buffer *eb)
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{
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if (down_read_trylock(&eb->lock)) {
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trace_btrfs_try_tree_read_lock(eb);
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return 1;
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}
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return 0;
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}
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/*
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* Try-lock for write.
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*
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* Return 1 if the rwlock has been taken, 0 otherwise
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*/
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int btrfs_try_tree_write_lock(struct extent_buffer *eb)
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{
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if (down_write_trylock(&eb->lock)) {
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eb->lock_owner = current->pid;
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trace_btrfs_try_tree_write_lock(eb);
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return 1;
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}
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return 0;
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}
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/*
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* Release read lock.
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*/
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void btrfs_tree_read_unlock(struct extent_buffer *eb)
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{
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trace_btrfs_tree_read_unlock(eb);
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up_read(&eb->lock);
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}
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/*
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* __btrfs_tree_lock - lock eb for write
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* @eb: the eb to lock
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* @nest: the nesting to use for the lock
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*
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* Returns with the eb->lock write locked.
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*/
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void __btrfs_tree_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest)
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__acquires(&eb->lock)
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{
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u64 start_ns = 0;
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if (trace_btrfs_tree_lock_enabled())
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start_ns = ktime_get_ns();
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down_write_nested(&eb->lock, nest);
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eb->lock_owner = current->pid;
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trace_btrfs_tree_lock(eb, start_ns);
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}
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void btrfs_tree_lock(struct extent_buffer *eb)
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{
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__btrfs_tree_lock(eb, BTRFS_NESTING_NORMAL);
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}
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/*
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* Release the write lock.
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*/
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void btrfs_tree_unlock(struct extent_buffer *eb)
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{
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trace_btrfs_tree_unlock(eb);
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eb->lock_owner = 0;
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up_write(&eb->lock);
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}
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/*
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* This releases any locks held in the path starting at level and going all the
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* way up to the root.
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*
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* btrfs_search_slot will keep the lock held on higher nodes in a few corner
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* cases, such as COW of the block at slot zero in the node. This ignores
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* those rules, and it should only be called when there are no more updates to
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* be done higher up in the tree.
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*/
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void btrfs_unlock_up_safe(struct btrfs_path *path, int level)
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{
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int i;
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if (path->keep_locks)
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return;
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for (i = level; i < BTRFS_MAX_LEVEL; i++) {
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if (!path->nodes[i])
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continue;
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if (!path->locks[i])
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continue;
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btrfs_tree_unlock_rw(path->nodes[i], path->locks[i]);
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path->locks[i] = 0;
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}
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}
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/*
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* Loop around taking references on and locking the root node of the tree until
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* we end up with a lock on the root node.
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*
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* Return: root extent buffer with write lock held
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*/
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struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root)
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{
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struct extent_buffer *eb;
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while (1) {
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eb = btrfs_root_node(root);
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btrfs_maybe_reset_lockdep_class(root, eb);
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btrfs_tree_lock(eb);
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if (eb == root->node)
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break;
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btrfs_tree_unlock(eb);
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free_extent_buffer(eb);
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}
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return eb;
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}
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/*
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* Loop around taking references on and locking the root node of the tree until
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* we end up with a lock on the root node.
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*
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* Return: root extent buffer with read lock held
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*/
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struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root)
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{
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struct extent_buffer *eb;
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while (1) {
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eb = btrfs_root_node(root);
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btrfs_maybe_reset_lockdep_class(root, eb);
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btrfs_tree_read_lock(eb);
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if (eb == root->node)
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break;
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btrfs_tree_read_unlock(eb);
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free_extent_buffer(eb);
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}
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return eb;
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}
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/*
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* Loop around taking references on and locking the root node of the tree in
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* nowait mode until we end up with a lock on the root node or returning to
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* avoid blocking.
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*
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* Return: root extent buffer with read lock held or -EAGAIN.
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*/
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struct extent_buffer *btrfs_try_read_lock_root_node(struct btrfs_root *root)
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{
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struct extent_buffer *eb;
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while (1) {
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eb = btrfs_root_node(root);
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if (!btrfs_try_tree_read_lock(eb)) {
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free_extent_buffer(eb);
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return ERR_PTR(-EAGAIN);
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}
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if (eb == root->node)
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break;
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btrfs_tree_read_unlock(eb);
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free_extent_buffer(eb);
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}
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return eb;
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}
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/*
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* DREW locks
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* ==========
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*
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* DREW stands for double-reader-writer-exclusion lock. It's used in situation
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* where you want to provide A-B exclusion but not AA or BB.
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*
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* Currently implementation gives more priority to reader. If a reader and a
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* writer both race to acquire their respective sides of the lock the writer
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* would yield its lock as soon as it detects a concurrent reader. Additionally
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* if there are pending readers no new writers would be allowed to come in and
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* acquire the lock.
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*/
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int btrfs_drew_lock_init(struct btrfs_drew_lock *lock)
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{
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int ret;
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ret = percpu_counter_init(&lock->writers, 0, GFP_KERNEL);
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if (ret)
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return ret;
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atomic_set(&lock->readers, 0);
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init_waitqueue_head(&lock->pending_readers);
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init_waitqueue_head(&lock->pending_writers);
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return 0;
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}
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void btrfs_drew_lock_destroy(struct btrfs_drew_lock *lock)
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{
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percpu_counter_destroy(&lock->writers);
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}
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/* Return true if acquisition is successful, false otherwise */
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bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock)
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{
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if (atomic_read(&lock->readers))
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return false;
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percpu_counter_inc(&lock->writers);
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/* Ensure writers count is updated before we check for pending readers */
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smp_mb();
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if (atomic_read(&lock->readers)) {
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btrfs_drew_write_unlock(lock);
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return false;
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}
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return true;
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}
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void btrfs_drew_write_lock(struct btrfs_drew_lock *lock)
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{
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while (true) {
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if (btrfs_drew_try_write_lock(lock))
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return;
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wait_event(lock->pending_writers, !atomic_read(&lock->readers));
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}
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}
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void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock)
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||
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{
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||
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|
percpu_counter_dec(&lock->writers);
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||
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cond_wake_up(&lock->pending_readers);
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||
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}
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||
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||
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void btrfs_drew_read_lock(struct btrfs_drew_lock *lock)
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||
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|
{
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||
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|
atomic_inc(&lock->readers);
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||
|
|
|
||
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|
/*
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||
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|
* Ensure the pending reader count is perceieved BEFORE this reader
|
||
|
|
* goes to sleep in case of active writers. This guarantees new writers
|
||
|
|
* won't be allowed and that the current reader will be woken up when
|
||
|
|
* the last active writer finishes its jobs.
|
||
|
|
*/
|
||
|
|
smp_mb__after_atomic();
|
||
|
|
|
||
|
|
wait_event(lock->pending_readers,
|
||
|
|
percpu_counter_sum(&lock->writers) == 0);
|
||
|
|
}
|
||
|
|
|
||
|
|
void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock)
|
||
|
|
{
|
||
|
|
/*
|
||
|
|
* atomic_dec_and_test implies a full barrier, so woken up writers
|
||
|
|
* are guaranteed to see the decrement
|
||
|
|
*/
|
||
|
|
if (atomic_dec_and_test(&lock->readers))
|
||
|
|
wake_up(&lock->pending_writers);
|
||
|
|
}
|