312 lines
8.3 KiB
C
312 lines
8.3 KiB
C
/*
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* Copyright (C) 2008 Oracle. All rights reserved.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public
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* License v2 as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public
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* License along with this program; if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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* Boston, MA 021110-1307, USA.
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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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/*
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* if we currently have a spinning reader or writer lock
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* (indicated by the rw flag) this will bump the count
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* of blocking holders and drop the spinlock.
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*/
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void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw)
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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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if (rw == BTRFS_WRITE_LOCK) {
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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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} else if (rw == BTRFS_READ_LOCK) {
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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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}
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/*
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* if we currently have a blocking lock, take the spinlock
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* and drop our blocking count
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*/
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void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
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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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if (rw == BTRFS_WRITE_LOCK_BLOCKING) {
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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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/*
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* atomic_dec_and_test implies a barrier for waitqueue_active
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*/
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if (atomic_dec_and_test(&eb->blocking_writers) &&
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waitqueue_active(&eb->write_lock_wq))
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wake_up(&eb->write_lock_wq);
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} else if (rw == BTRFS_READ_LOCK_BLOCKING) {
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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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/*
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* atomic_dec_and_test implies a barrier for waitqueue_active
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*/
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if (atomic_dec_and_test(&eb->blocking_readers) &&
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waitqueue_active(&eb->read_lock_wq))
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wake_up(&eb->read_lock_wq);
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}
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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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/*
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* atomic_dec_and_test implies a barrier for waitqueue_active
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*/
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if (atomic_dec_and_test(&eb->blocking_readers) &&
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waitqueue_active(&eb->read_lock_wq))
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wake_up(&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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write_unlock(&eb->lock);
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wait_event(eb->read_lock_wq,
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atomic_read(&eb->blocking_readers) == 0);
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goto again;
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}
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if (atomic_read(&eb->blocking_writers)) {
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write_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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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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/*
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* Make sure counter is updated before we wake up waiters.
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*/
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smp_mb();
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if (waitqueue_active(&eb->write_lock_wq))
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wake_up(&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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