Loading...
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 | /*
* Copyright (C) 2008 Oracle. All rights reserved.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public
* License v2 as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public
* License along with this program; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 021110-1307, USA.
*/
#include <linux/sched.h>
#include <linux/pagemap.h>
#include <linux/spinlock.h>
#include <linux/page-flags.h>
#include <asm/bug.h>
#include "ctree.h"
#include "extent_io.h"
#include "locking.h"
static void btrfs_assert_tree_read_locked(struct extent_buffer *eb);
/*
* if we currently have a spinning reader or writer lock
* (indicated by the rw flag) this will bump the count
* of blocking holders and drop the spinlock.
*/
void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw)
{
/*
* no lock is required. The lock owner may change if
* we have a read lock, but it won't change to or away
* from us. If we have the write lock, we are the owner
* and it'll never change.
*/
if (eb->lock_nested && current->pid == eb->lock_owner)
return;
if (rw == BTRFS_WRITE_LOCK) {
if (atomic_read(&eb->blocking_writers) == 0) {
WARN_ON(atomic_read(&eb->spinning_writers) != 1);
atomic_dec(&eb->spinning_writers);
btrfs_assert_tree_locked(eb);
atomic_inc(&eb->blocking_writers);
write_unlock(&eb->lock);
}
} else if (rw == BTRFS_READ_LOCK) {
btrfs_assert_tree_read_locked(eb);
atomic_inc(&eb->blocking_readers);
WARN_ON(atomic_read(&eb->spinning_readers) == 0);
atomic_dec(&eb->spinning_readers);
read_unlock(&eb->lock);
}
return;
}
/*
* if we currently have a blocking lock, take the spinlock
* and drop our blocking count
*/
void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
{
/*
* no lock is required. The lock owner may change if
* we have a read lock, but it won't change to or away
* from us. If we have the write lock, we are the owner
* and it'll never change.
*/
if (eb->lock_nested && current->pid == eb->lock_owner)
return;
if (rw == BTRFS_WRITE_LOCK_BLOCKING) {
BUG_ON(atomic_read(&eb->blocking_writers) != 1);
write_lock(&eb->lock);
WARN_ON(atomic_read(&eb->spinning_writers));
atomic_inc(&eb->spinning_writers);
if (atomic_dec_and_test(&eb->blocking_writers) &&
waitqueue_active(&eb->write_lock_wq))
wake_up(&eb->write_lock_wq);
} else if (rw == BTRFS_READ_LOCK_BLOCKING) {
BUG_ON(atomic_read(&eb->blocking_readers) == 0);
read_lock(&eb->lock);
atomic_inc(&eb->spinning_readers);
if (atomic_dec_and_test(&eb->blocking_readers) &&
waitqueue_active(&eb->read_lock_wq))
wake_up(&eb->read_lock_wq);
}
return;
}
/*
* take a spinning read lock. This will wait for any blocking
* writers
*/
void btrfs_tree_read_lock(struct extent_buffer *eb)
{
again:
BUG_ON(!atomic_read(&eb->blocking_writers) &&
current->pid == eb->lock_owner);
read_lock(&eb->lock);
if (atomic_read(&eb->blocking_writers) &&
current->pid == eb->lock_owner) {
/*
* This extent is already write-locked by our thread. We allow
* an additional read lock to be added because it's for the same
* thread. btrfs_find_all_roots() depends on this as it may be
* called on a partly (write-)locked tree.
*/
BUG_ON(eb->lock_nested);
eb->lock_nested = 1;
read_unlock(&eb->lock);
return;
}
if (atomic_read(&eb->blocking_writers)) {
read_unlock(&eb->lock);
wait_event(eb->write_lock_wq,
atomic_read(&eb->blocking_writers) == 0);
goto again;
}
atomic_inc(&eb->read_locks);
atomic_inc(&eb->spinning_readers);
}
/*
* take a spinning read lock.
* returns 1 if we get the read lock and 0 if we don't
* this won't wait for blocking writers
*/
int btrfs_tree_read_lock_atomic(struct extent_buffer *eb)
{
if (atomic_read(&eb->blocking_writers))
return 0;
read_lock(&eb->lock);
if (atomic_read(&eb->blocking_writers)) {
read_unlock(&eb->lock);
return 0;
}
atomic_inc(&eb->read_locks);
atomic_inc(&eb->spinning_readers);
return 1;
}
/*
* returns 1 if we get the read lock and 0 if we don't
* this won't wait for blocking writers
*/
int btrfs_try_tree_read_lock(struct extent_buffer *eb)
{
if (atomic_read(&eb->blocking_writers))
return 0;
if (!read_trylock(&eb->lock))
return 0;
if (atomic_read(&eb->blocking_writers)) {
read_unlock(&eb->lock);
return 0;
}
atomic_inc(&eb->read_locks);
atomic_inc(&eb->spinning_readers);
return 1;
}
/*
* returns 1 if we get the read lock and 0 if we don't
* this won't wait for blocking writers or readers
*/
int btrfs_try_tree_write_lock(struct extent_buffer *eb)
{
if (atomic_read(&eb->blocking_writers) ||
atomic_read(&eb->blocking_readers))
return 0;
write_lock(&eb->lock);
if (atomic_read(&eb->blocking_writers) ||
atomic_read(&eb->blocking_readers)) {
write_unlock(&eb->lock);
return 0;
}
atomic_inc(&eb->write_locks);
atomic_inc(&eb->spinning_writers);
eb->lock_owner = current->pid;
return 1;
}
/*
* drop a spinning read lock
*/
void btrfs_tree_read_unlock(struct extent_buffer *eb)
{
/*
* if we're nested, we have the write lock. No new locking
* is needed as long as we are the lock owner.
* The write unlock will do a barrier for us, and the lock_nested
* field only matters to the lock owner.
*/
if (eb->lock_nested && current->pid == eb->lock_owner) {
eb->lock_nested = 0;
return;
}
btrfs_assert_tree_read_locked(eb);
WARN_ON(atomic_read(&eb->spinning_readers) == 0);
atomic_dec(&eb->spinning_readers);
atomic_dec(&eb->read_locks);
read_unlock(&eb->lock);
}
/*
* drop a blocking read lock
*/
void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
{
/*
* if we're nested, we have the write lock. No new locking
* is needed as long as we are the lock owner.
* The write unlock will do a barrier for us, and the lock_nested
* field only matters to the lock owner.
*/
if (eb->lock_nested && current->pid == eb->lock_owner) {
eb->lock_nested = 0;
return;
}
btrfs_assert_tree_read_locked(eb);
WARN_ON(atomic_read(&eb->blocking_readers) == 0);
if (atomic_dec_and_test(&eb->blocking_readers) &&
waitqueue_active(&eb->read_lock_wq))
wake_up(&eb->read_lock_wq);
atomic_dec(&eb->read_locks);
}
/*
* take a spinning write lock. This will wait for both
* blocking readers or writers
*/
void btrfs_tree_lock(struct extent_buffer *eb)
{
again:
wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
write_lock(&eb->lock);
if (atomic_read(&eb->blocking_readers)) {
write_unlock(&eb->lock);
wait_event(eb->read_lock_wq,
atomic_read(&eb->blocking_readers) == 0);
goto again;
}
if (atomic_read(&eb->blocking_writers)) {
write_unlock(&eb->lock);
wait_event(eb->write_lock_wq,
atomic_read(&eb->blocking_writers) == 0);
goto again;
}
WARN_ON(atomic_read(&eb->spinning_writers));
atomic_inc(&eb->spinning_writers);
atomic_inc(&eb->write_locks);
eb->lock_owner = current->pid;
}
/*
* drop a spinning or a blocking write lock.
*/
void btrfs_tree_unlock(struct extent_buffer *eb)
{
int blockers = atomic_read(&eb->blocking_writers);
BUG_ON(blockers > 1);
btrfs_assert_tree_locked(eb);
eb->lock_owner = 0;
atomic_dec(&eb->write_locks);
if (blockers) {
WARN_ON(atomic_read(&eb->spinning_writers));
atomic_dec(&eb->blocking_writers);
smp_mb();
if (waitqueue_active(&eb->write_lock_wq))
wake_up(&eb->write_lock_wq);
} else {
WARN_ON(atomic_read(&eb->spinning_writers) != 1);
atomic_dec(&eb->spinning_writers);
write_unlock(&eb->lock);
}
}
void btrfs_assert_tree_locked(struct extent_buffer *eb)
{
BUG_ON(!atomic_read(&eb->write_locks));
}
static void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
{
BUG_ON(!atomic_read(&eb->read_locks));
}
|