286 lines
7.5 KiB
C
286 lines
7.5 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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#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 "ctree.h"
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#include "extent_io.h"
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#include "locking.h"
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static void btrfs_assert_tree_read_locked(struct extent_buffer *eb);
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void btrfs_set_lock_blocking_read(struct extent_buffer *eb)
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{
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/*
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* No lock is required. The lock owner may change if we have a read
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* lock, but it won't change to or away from us. If we have the write
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* lock, we are the owner and it'll never change.
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*/
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if (eb->lock_nested && current->pid == eb->lock_owner)
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return;
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btrfs_assert_tree_read_locked(eb);
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atomic_inc(&eb->blocking_readers);
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WARN_ON(atomic_read(&eb->spinning_readers) == 0);
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atomic_dec(&eb->spinning_readers);
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read_unlock(&eb->lock);
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}
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void btrfs_set_lock_blocking_write(struct extent_buffer *eb)
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{
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/*
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* No lock is required. The lock owner may change if we have a read
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* lock, but it won't change to or away from us. If we have the write
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* lock, we are the owner and it'll never change.
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*/
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if (eb->lock_nested && current->pid == eb->lock_owner)
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return;
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if (atomic_read(&eb->blocking_writers) == 0) {
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WARN_ON(atomic_read(&eb->spinning_writers) != 1);
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atomic_dec(&eb->spinning_writers);
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btrfs_assert_tree_locked(eb);
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atomic_inc(&eb->blocking_writers);
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write_unlock(&eb->lock);
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}
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}
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void btrfs_clear_lock_blocking_read(struct extent_buffer *eb)
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{
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/*
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* No lock is required. The lock owner may change if we have a read
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* lock, but it won't change to or away from us. If we have the write
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* lock, we are the owner and it'll never change.
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*/
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if (eb->lock_nested && current->pid == eb->lock_owner)
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return;
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BUG_ON(atomic_read(&eb->blocking_readers) == 0);
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read_lock(&eb->lock);
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atomic_inc(&eb->spinning_readers);
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/* atomic_dec_and_test implies a barrier */
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if (atomic_dec_and_test(&eb->blocking_readers))
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cond_wake_up_nomb(&eb->read_lock_wq);
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}
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void btrfs_clear_lock_blocking_write(struct extent_buffer *eb)
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{
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/*
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* no lock is required. The lock owner may change if
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* we have a read lock, but it won't change to or away
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* from us. If we have the write lock, we are the owner
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* and it'll never change.
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*/
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if (eb->lock_nested && current->pid == eb->lock_owner)
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return;
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BUG_ON(atomic_read(&eb->blocking_writers) != 1);
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write_lock(&eb->lock);
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WARN_ON(atomic_read(&eb->spinning_writers));
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atomic_inc(&eb->spinning_writers);
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/* atomic_dec_and_test implies a barrier */
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if (atomic_dec_and_test(&eb->blocking_writers))
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cond_wake_up_nomb(&eb->write_lock_wq);
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}
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/*
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* take a spinning read lock. This will wait for any blocking
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* writers
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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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again:
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BUG_ON(!atomic_read(&eb->blocking_writers) &&
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current->pid == eb->lock_owner);
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read_lock(&eb->lock);
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if (atomic_read(&eb->blocking_writers) &&
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current->pid == eb->lock_owner) {
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/*
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* This extent is already write-locked by our thread. We allow
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* an additional read lock to be added because it's for the same
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* thread. btrfs_find_all_roots() depends on this as it may be
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* called on a partly (write-)locked tree.
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*/
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BUG_ON(eb->lock_nested);
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eb->lock_nested = 1;
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read_unlock(&eb->lock);
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return;
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}
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if (atomic_read(&eb->blocking_writers)) {
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read_unlock(&eb->lock);
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wait_event(eb->write_lock_wq,
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atomic_read(&eb->blocking_writers) == 0);
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goto again;
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}
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atomic_inc(&eb->read_locks);
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atomic_inc(&eb->spinning_readers);
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}
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/*
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* take a spinning read lock.
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* returns 1 if we get the read lock and 0 if we don't
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* this won't wait for blocking writers
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*/
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int btrfs_tree_read_lock_atomic(struct extent_buffer *eb)
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{
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if (atomic_read(&eb->blocking_writers))
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return 0;
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read_lock(&eb->lock);
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if (atomic_read(&eb->blocking_writers)) {
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read_unlock(&eb->lock);
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return 0;
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}
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atomic_inc(&eb->read_locks);
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atomic_inc(&eb->spinning_readers);
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return 1;
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}
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/*
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* returns 1 if we get the read lock and 0 if we don't
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* this won't wait for blocking writers
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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 (atomic_read(&eb->blocking_writers))
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return 0;
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if (!read_trylock(&eb->lock))
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return 0;
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if (atomic_read(&eb->blocking_writers)) {
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read_unlock(&eb->lock);
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return 0;
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}
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atomic_inc(&eb->read_locks);
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atomic_inc(&eb->spinning_readers);
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return 1;
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}
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/*
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* returns 1 if we get the read lock and 0 if we don't
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* this won't wait for blocking writers or readers
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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 (atomic_read(&eb->blocking_writers) ||
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atomic_read(&eb->blocking_readers))
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return 0;
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write_lock(&eb->lock);
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if (atomic_read(&eb->blocking_writers) ||
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atomic_read(&eb->blocking_readers)) {
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write_unlock(&eb->lock);
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return 0;
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}
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atomic_inc(&eb->write_locks);
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atomic_inc(&eb->spinning_writers);
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eb->lock_owner = current->pid;
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return 1;
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}
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/*
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* drop a spinning 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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/*
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* if we're nested, we have the write lock. No new locking
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* is needed as long as we are the lock owner.
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* The write unlock will do a barrier for us, and the lock_nested
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* field only matters to the lock owner.
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*/
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if (eb->lock_nested && current->pid == eb->lock_owner) {
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eb->lock_nested = 0;
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return;
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}
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btrfs_assert_tree_read_locked(eb);
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WARN_ON(atomic_read(&eb->spinning_readers) == 0);
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atomic_dec(&eb->spinning_readers);
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atomic_dec(&eb->read_locks);
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read_unlock(&eb->lock);
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}
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/*
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* drop a blocking read lock
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*/
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void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
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{
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/*
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* if we're nested, we have the write lock. No new locking
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* is needed as long as we are the lock owner.
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* The write unlock will do a barrier for us, and the lock_nested
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* field only matters to the lock owner.
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*/
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if (eb->lock_nested && current->pid == eb->lock_owner) {
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eb->lock_nested = 0;
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return;
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}
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btrfs_assert_tree_read_locked(eb);
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WARN_ON(atomic_read(&eb->blocking_readers) == 0);
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/* atomic_dec_and_test implies a barrier */
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if (atomic_dec_and_test(&eb->blocking_readers))
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cond_wake_up_nomb(&eb->read_lock_wq);
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atomic_dec(&eb->read_locks);
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}
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/*
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* take a spinning write lock. This will wait for both
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* blocking readers or writers
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*/
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void btrfs_tree_lock(struct extent_buffer *eb)
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{
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WARN_ON(eb->lock_owner == current->pid);
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again:
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wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
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wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
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write_lock(&eb->lock);
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if (atomic_read(&eb->blocking_readers) ||
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atomic_read(&eb->blocking_writers)) {
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write_unlock(&eb->lock);
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goto again;
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}
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WARN_ON(atomic_read(&eb->spinning_writers));
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atomic_inc(&eb->spinning_writers);
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atomic_inc(&eb->write_locks);
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eb->lock_owner = current->pid;
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}
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/*
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* drop a spinning or a blocking 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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int blockers = atomic_read(&eb->blocking_writers);
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BUG_ON(blockers > 1);
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btrfs_assert_tree_locked(eb);
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eb->lock_owner = 0;
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atomic_dec(&eb->write_locks);
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if (blockers) {
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WARN_ON(atomic_read(&eb->spinning_writers));
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atomic_dec(&eb->blocking_writers);
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/* Use the lighter barrier after atomic */
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smp_mb__after_atomic();
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cond_wake_up_nomb(&eb->write_lock_wq);
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} else {
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WARN_ON(atomic_read(&eb->spinning_writers) != 1);
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atomic_dec(&eb->spinning_writers);
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write_unlock(&eb->lock);
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}
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}
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void btrfs_assert_tree_locked(struct extent_buffer *eb)
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{
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BUG_ON(!atomic_read(&eb->write_locks));
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}
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static void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
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{
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BUG_ON(!atomic_read(&eb->read_locks));
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}
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