Commit | Line | Data |
---|---|---|
925baedd CM |
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> | |
4881ee5a | 23 | #include <asm/bug.h> |
925baedd CM |
24 | #include "ctree.h" |
25 | #include "extent_io.h" | |
26 | #include "locking.h" | |
27 | ||
b4ce94de CM |
28 | static inline void spin_nested(struct extent_buffer *eb) |
29 | { | |
30 | spin_lock(&eb->lock); | |
31 | } | |
d397712b | 32 | |
b4ce94de CM |
33 | /* |
34 | * Setting a lock to blocking will drop the spinlock and set the | |
35 | * flag that forces other procs who want the lock to wait. After | |
36 | * this you can safely schedule with the lock held. | |
37 | */ | |
38 | void btrfs_set_lock_blocking(struct extent_buffer *eb) | |
925baedd | 39 | { |
b4ce94de CM |
40 | if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) { |
41 | set_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags); | |
42 | spin_unlock(&eb->lock); | |
43 | } | |
44 | /* exit with the spin lock released and the bit set */ | |
45 | } | |
f9efa9c7 | 46 | |
b4ce94de CM |
47 | /* |
48 | * clearing the blocking flag will take the spinlock again. | |
49 | * After this you can't safely schedule | |
50 | */ | |
51 | void btrfs_clear_lock_blocking(struct extent_buffer *eb) | |
52 | { | |
53 | if (test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) { | |
54 | spin_nested(eb); | |
55 | clear_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags); | |
56 | smp_mb__after_clear_bit(); | |
57 | } | |
58 | /* exit with the spin lock held */ | |
59 | } | |
60 | ||
61 | /* | |
62 | * unfortunately, many of the places that currently set a lock to blocking | |
63 | * don't end up blocking for every long, and often they don't block | |
64 | * at all. For a dbench 50 run, if we don't spin one the blocking bit | |
65 | * at all, the context switch rate can jump up to 400,000/sec or more. | |
66 | * | |
67 | * So, we're still stuck with this crummy spin on the blocking bit, | |
68 | * at least until the most common causes of the short blocks | |
69 | * can be dealt with. | |
70 | */ | |
71 | static int btrfs_spin_on_block(struct extent_buffer *eb) | |
72 | { | |
73 | int i; | |
f9efa9c7 CM |
74 | for (i = 0; i < 512; i++) { |
75 | cpu_relax(); | |
b4ce94de CM |
76 | if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) |
77 | return 1; | |
78 | if (need_resched()) | |
79 | break; | |
80 | } | |
81 | return 0; | |
82 | } | |
83 | ||
84 | /* | |
85 | * This is somewhat different from trylock. It will take the | |
86 | * spinlock but if it finds the lock is set to blocking, it will | |
87 | * return without the lock held. | |
88 | * | |
89 | * returns 1 if it was able to take the lock and zero otherwise | |
90 | * | |
91 | * After this call, scheduling is not safe without first calling | |
92 | * btrfs_set_lock_blocking() | |
93 | */ | |
94 | int btrfs_try_spin_lock(struct extent_buffer *eb) | |
95 | { | |
96 | int i; | |
97 | ||
98 | spin_nested(eb); | |
99 | if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) | |
100 | return 1; | |
101 | spin_unlock(&eb->lock); | |
102 | ||
103 | /* spin for a bit on the BLOCKING flag */ | |
104 | for (i = 0; i < 2; i++) { | |
105 | if (!btrfs_spin_on_block(eb)) | |
106 | break; | |
107 | ||
108 | spin_nested(eb); | |
109 | if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) | |
110 | return 1; | |
111 | spin_unlock(&eb->lock); | |
112 | } | |
113 | return 0; | |
114 | } | |
115 | ||
116 | /* | |
117 | * the autoremove wake function will return 0 if it tried to wake up | |
118 | * a process that was already awake, which means that process won't | |
119 | * count as an exclusive wakeup. The waitq code will continue waking | |
120 | * procs until it finds one that was actually sleeping. | |
121 | * | |
122 | * For btrfs, this isn't quite what we want. We want a single proc | |
123 | * to be notified that the lock is ready for taking. If that proc | |
124 | * already happen to be awake, great, it will loop around and try for | |
125 | * the lock. | |
126 | * | |
127 | * So, btrfs_wake_function always returns 1, even when the proc that we | |
128 | * tried to wake up was already awake. | |
129 | */ | |
130 | static int btrfs_wake_function(wait_queue_t *wait, unsigned mode, | |
131 | int sync, void *key) | |
132 | { | |
133 | autoremove_wake_function(wait, mode, sync, key); | |
134 | return 1; | |
135 | } | |
136 | ||
137 | /* | |
138 | * returns with the extent buffer spinlocked. | |
139 | * | |
140 | * This will spin and/or wait as required to take the lock, and then | |
141 | * return with the spinlock held. | |
142 | * | |
143 | * After this call, scheduling is not safe without first calling | |
144 | * btrfs_set_lock_blocking() | |
145 | */ | |
146 | int btrfs_tree_lock(struct extent_buffer *eb) | |
147 | { | |
148 | DEFINE_WAIT(wait); | |
149 | wait.func = btrfs_wake_function; | |
150 | ||
151 | while(1) { | |
152 | spin_nested(eb); | |
153 | ||
154 | /* nobody is blocking, exit with the spinlock held */ | |
155 | if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) | |
f9efa9c7 | 156 | return 0; |
b4ce94de CM |
157 | |
158 | /* | |
159 | * we have the spinlock, but the real owner is blocking. | |
160 | * wait for them | |
161 | */ | |
162 | spin_unlock(&eb->lock); | |
163 | ||
164 | /* | |
165 | * spin for a bit, and if the blocking flag goes away, | |
166 | * loop around | |
167 | */ | |
168 | if (btrfs_spin_on_block(eb)) | |
169 | continue; | |
170 | ||
171 | prepare_to_wait_exclusive(&eb->lock_wq, &wait, | |
172 | TASK_UNINTERRUPTIBLE); | |
173 | ||
174 | if (test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) | |
175 | schedule(); | |
176 | ||
177 | finish_wait(&eb->lock_wq, &wait); | |
f9efa9c7 | 178 | } |
925baedd CM |
179 | return 0; |
180 | } | |
181 | ||
b4ce94de CM |
182 | /* |
183 | * Very quick trylock, this does not spin or schedule. It returns | |
184 | * 1 with the spinlock held if it was able to take the lock, or it | |
185 | * returns zero if it was unable to take the lock. | |
186 | * | |
187 | * After this call, scheduling is not safe without first calling | |
188 | * btrfs_set_lock_blocking() | |
189 | */ | |
925baedd CM |
190 | int btrfs_try_tree_lock(struct extent_buffer *eb) |
191 | { | |
b4ce94de CM |
192 | if (spin_trylock(&eb->lock)) { |
193 | if (test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) { | |
194 | /* | |
195 | * we've got the spinlock, but the real owner is | |
196 | * blocking. Drop the spinlock and return failure | |
197 | */ | |
198 | spin_unlock(&eb->lock); | |
199 | return 0; | |
200 | } | |
201 | return 1; | |
202 | } | |
203 | /* someone else has the spinlock giveup */ | |
204 | return 0; | |
925baedd CM |
205 | } |
206 | ||
207 | int btrfs_tree_unlock(struct extent_buffer *eb) | |
208 | { | |
b4ce94de CM |
209 | /* |
210 | * if we were a blocking owner, we don't have the spinlock held | |
211 | * just clear the bit and look for waiters | |
212 | */ | |
213 | if (test_and_clear_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) | |
214 | smp_mb__after_clear_bit(); | |
215 | else | |
216 | spin_unlock(&eb->lock); | |
217 | ||
218 | if (waitqueue_active(&eb->lock_wq)) | |
219 | wake_up(&eb->lock_wq); | |
925baedd CM |
220 | return 0; |
221 | } | |
222 | ||
223 | int btrfs_tree_locked(struct extent_buffer *eb) | |
224 | { | |
b4ce94de CM |
225 | return test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags) || |
226 | spin_is_locked(&eb->lock); | |
925baedd | 227 | } |