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291 lines
6.6 KiB
291 lines
6.6 KiB
// 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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/* |
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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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eb->lock_owner = current->pid; |
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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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* Retrun 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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eb->lock_owner = current->pid; |
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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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* Retrun 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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eb->lock_owner = 0; |
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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_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_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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* 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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percpu_counter_dec(&lock->writers); |
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cond_wake_up(&lock->pending_readers); |
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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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atomic_inc(&lock->readers); |
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/* |
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* Ensure the pending reader count is perceieved BEFORE this reader |
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* goes to sleep in case of active writers. This guarantees new writers |
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* won't be allowed and that the current reader will be woken up when |
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* the last active writer finishes its jobs. |
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*/ |
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smp_mb__after_atomic(); |
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wait_event(lock->pending_readers, |
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percpu_counter_sum(&lock->writers) == 0); |
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} |
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void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock) |
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{ |
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/* |
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* atomic_dec_and_test implies a full barrier, so woken up writers |
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* are guaranteed to see the decrement |
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*/ |
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if (atomic_dec_and_test(&lock->readers)) |
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wake_up(&lock->pending_writers); |
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}
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