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diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
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1/*
2 * Copyright (C) 2008 Oracle. All rights reserved.
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public
6 * License v2 as published by the Free Software Foundation.
7 *
8 * This program is distributed in the hope that it will be useful,
9 * but WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
11 * General Public License for more details.
12 *
13 * You should have received a copy of the GNU General Public
14 * License along with this program; if not, write to the
15 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
16 * Boston, MA 021110-1307, USA.
17 */
18#include <linux/sched.h>
19#include <linux/gfp.h>
20#include <linux/pagemap.h>
21#include <linux/spinlock.h>
22#include <linux/page-flags.h>
23#include <asm/bug.h>
24#include "ctree.h"
25#include "extent_io.h"
26#include "locking.h"
27
28/*
29 * locks the per buffer mutex in an extent buffer. This uses adaptive locks
30 * and the spin is not tuned very extensively. The spinning does make a big
31 * difference in almost every workload, but spinning for the right amount of
32 * time needs some help.
33 *
34 * In general, we want to spin as long as the lock holder is doing btree
35 * searches, and we should give up if they are in more expensive code.
36 */
37
38int btrfs_tree_lock(struct extent_buffer *eb)
39{
40 int i;
41
42 if (mutex_trylock(&eb->mutex))
43 return 0;
44 for (i = 0; i < 512; i++) {
45 cpu_relax();
46 if (mutex_trylock(&eb->mutex))
47 return 0;
48 }
49 cpu_relax();
50 mutex_lock_nested(&eb->mutex, BTRFS_MAX_LEVEL - btrfs_header_level(eb));
51 return 0;
52}
53
54int btrfs_try_tree_lock(struct extent_buffer *eb)
55{
56 return mutex_trylock(&eb->mutex);
57}
58
59int btrfs_tree_unlock(struct extent_buffer *eb)
60{
61 mutex_unlock(&eb->mutex);
62 return 0;
63}
64
65int btrfs_tree_locked(struct extent_buffer *eb)
66{
67 return mutex_is_locked(&eb->mutex);
68}
69
70/*
71 * btrfs_search_slot uses this to decide if it should drop its locks
72 * before doing something expensive like allocating free blocks for cow.
73 */
74int btrfs_path_lock_waiting(struct btrfs_path *path, int level)
75{
76 int i;
77 struct extent_buffer *eb;
78 for (i = level; i <= level + 1 && i < BTRFS_MAX_LEVEL; i++) {
79 eb = path->nodes[i];
80 if (!eb)
81 break;
82 smp_mb();
83 if (!list_empty(&eb->mutex.wait_list))
84 return 1;
85 }
86 return 0;
87}
88