2992df7326
A (D)ouble (R)eader (W)riter (E)xclustion lock is a locking primitive that allows to have multiple readers or multiple writers but not multiple readers and writers holding it concurrently. The code is factored out from the existing open-coded locking scheme used to exclude pending snapshots from nocow writers and vice-versa. Current implementation actually favors Readers (that is snapshot creaters) to writers (nocow writers of the filesystem). The API provides lock/unlock/trylock for reads and writes. Formal specification for TLA+ provided by Valentin Schneider is at https://lore.kernel.org/linux-btrfs/2dcaf81c-f0d3-409e-cb29-733d8b3b4cc9@arm.com/ Signed-off-by: Nikolay Borisov <nborisov@suse.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
72 lines
2.1 KiB
C
72 lines
2.1 KiB
C
/* 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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#ifndef BTRFS_LOCKING_H
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#define BTRFS_LOCKING_H
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#include <linux/atomic.h>
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#include <linux/wait.h>
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#include <linux/percpu_counter.h>
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#include "extent_io.h"
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#define BTRFS_WRITE_LOCK 1
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#define BTRFS_READ_LOCK 2
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#define BTRFS_WRITE_LOCK_BLOCKING 3
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#define BTRFS_READ_LOCK_BLOCKING 4
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struct btrfs_path;
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void btrfs_tree_lock(struct extent_buffer *eb);
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void btrfs_tree_unlock(struct extent_buffer *eb);
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void btrfs_tree_read_lock(struct extent_buffer *eb);
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void btrfs_tree_read_unlock(struct extent_buffer *eb);
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void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb);
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void btrfs_set_lock_blocking_read(struct extent_buffer *eb);
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void btrfs_set_lock_blocking_write(struct extent_buffer *eb);
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int btrfs_try_tree_read_lock(struct extent_buffer *eb);
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int btrfs_try_tree_write_lock(struct extent_buffer *eb);
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int btrfs_tree_read_lock_atomic(struct extent_buffer *eb);
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#ifdef CONFIG_BTRFS_DEBUG
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static inline void btrfs_assert_tree_locked(struct extent_buffer *eb) {
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BUG_ON(!eb->write_locks);
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}
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#else
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static inline void btrfs_assert_tree_locked(struct extent_buffer *eb) { }
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#endif
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void btrfs_set_path_blocking(struct btrfs_path *p);
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void btrfs_unlock_up_safe(struct btrfs_path *path, int level);
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static inline void btrfs_tree_unlock_rw(struct extent_buffer *eb, int rw)
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{
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if (rw == BTRFS_WRITE_LOCK || rw == BTRFS_WRITE_LOCK_BLOCKING)
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btrfs_tree_unlock(eb);
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else if (rw == BTRFS_READ_LOCK_BLOCKING)
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btrfs_tree_read_unlock_blocking(eb);
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else if (rw == BTRFS_READ_LOCK)
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btrfs_tree_read_unlock(eb);
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else
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BUG();
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}
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struct btrfs_drew_lock {
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atomic_t readers;
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struct percpu_counter writers;
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wait_queue_head_t pending_writers;
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wait_queue_head_t pending_readers;
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};
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int btrfs_drew_lock_init(struct btrfs_drew_lock *lock);
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void btrfs_drew_lock_destroy(struct btrfs_drew_lock *lock);
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void btrfs_drew_write_lock(struct btrfs_drew_lock *lock);
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bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock);
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void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock);
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void btrfs_drew_read_lock(struct btrfs_drew_lock *lock);
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void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock);
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#endif
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