fs/btrfs/locking.c

   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/pagemap.h>
  20 #include <linux/spinlock.h>
  21 #include <linux/page-flags.h>
  22 #include <asm/bug.h>
  23 #include "ctree.h"
  24 #include "extent_io.h"
  25 #include "locking.h"
  26
  27 void btrfs_assert_tree_read_locked(struct extent_buffer *eb);
  28
  29 /*
  30  * if we currently have a spinning reader or writer lock
  31  * (indicated by the rw flag) this will bump the count
  32  * of blocking holders and drop the spinlock.
  33  */
  34 void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw)
  35 {
  36         if (eb->lock_nested) {
  37                 read_lock(&eb->lock);
  38                 if (eb->lock_nested && current->pid == eb->lock_owner) {
  39                         read_unlock(&eb->lock);
  40                         return;
  41                 }
  42                 read_unlock(&eb->lock);
  43         }
  44         if (rw == BTRFS_WRITE_LOCK) {
  45                 if (atomic_read(&eb->blocking_writers) == 0) {
  46                         WARN_ON(atomic_read(&eb->spinning_writers) != 1);
  47                         atomic_dec(&eb->spinning_writers);
  48                         btrfs_assert_tree_locked(eb);
  49                         atomic_inc(&eb->blocking_writers);
  50                         write_unlock(&eb->lock);
  51                 }
  52         } else if (rw == BTRFS_READ_LOCK) {
  53                 btrfs_assert_tree_read_locked(eb);
  54                 atomic_inc(&eb->blocking_readers);
  55                 WARN_ON(atomic_read(&eb->spinning_readers) == 0);
  56                 atomic_dec(&eb->spinning_readers);
  57                 read_unlock(&eb->lock);
  58         }
  59         return;
  60 }
  61
  62 /*
  63  * if we currently have a blocking lock, take the spinlock
  64  * and drop our blocking count
  65  */
  66 void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
  67 {
  68         if (eb->lock_nested) {
  69                 read_lock(&eb->lock);
  70                 if (eb->lock_nested && current->pid == eb->lock_owner) {
  71                         read_unlock(&eb->lock);
  72                         return;
  73                 }
  74                 read_unlock(&eb->lock);
  75         }
  76         if (rw == BTRFS_WRITE_LOCK_BLOCKING) {
  77                 BUG_ON(atomic_read(&eb->blocking_writers) != 1);
  78                 write_lock(&eb->lock);
  79                 WARN_ON(atomic_read(&eb->spinning_writers));
  80                 atomic_inc(&eb->spinning_writers);
  81                 if (atomic_dec_and_test(&eb->blocking_writers) &&
  82                     waitqueue_active(&eb->write_lock_wq))
  83                         wake_up(&eb->write_lock_wq);
  84         } else if (rw == BTRFS_READ_LOCK_BLOCKING) {
  85                 BUG_ON(atomic_read(&eb->blocking_readers) == 0);
  86                 read_lock(&eb->lock);
  87                 atomic_inc(&eb->spinning_readers);
  88                 if (atomic_dec_and_test(&eb->blocking_readers) &&
  89                     waitqueue_active(&eb->read_lock_wq))
  90                         wake_up(&eb->read_lock_wq);
  91         }
  92         return;
  93 }
  94
  95 /*
  96  * take a spinning read lock.  This will wait for any blocking
  97  * writers
  98  */
  99 void btrfs_tree_read_lock(struct extent_buffer *eb)
 100 {
 101 again:
 102         read_lock(&eb->lock);
 103         if (atomic_read(&eb->blocking_writers) &&
 104             current->pid == eb->lock_owner) {
 105                 /*
 106                  * This extent is already write-locked by our thread. We allow
 107                  * an additional read lock to be added because it's for the same
 108                  * thread. btrfs_find_all_roots() depends on this as it may be
 109                  * called on a partly (write-)locked tree.
 110                  */
 111                 BUG_ON(eb->lock_nested);
 112                 eb->lock_nested = 1;
 113                 read_unlock(&eb->lock);
 114                 return;
 115         }
 116         read_unlock(&eb->lock);
 117         wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
 118         read_lock(&eb->lock);
 119         if (atomic_read(&eb->blocking_writers)) {
 120                 read_unlock(&eb->lock);
 121                 goto again;
 122         }
 123         atomic_inc(&eb->read_locks);
 124         atomic_inc(&eb->spinning_readers);
 125 }
 126
 127 /*
 128  * returns 1 if we get the read lock and 0 if we don't
 129  * this won't wait for blocking writers
 130  */
 131 int btrfs_try_tree_read_lock(struct extent_buffer *eb)
 132 {
 133         if (atomic_read(&eb->blocking_writers))
 134                 return 0;
 135
 136         read_lock(&eb->lock);
 137         if (atomic_read(&eb->blocking_writers)) {
 138                 read_unlock(&eb->lock);
 139                 return 0;
 140         }
 141         atomic_inc(&eb->read_locks);
 142         atomic_inc(&eb->spinning_readers);
 143         return 1;
 144 }
 145
 146 /*
 147  * returns 1 if we get the read lock and 0 if we don't
 148  * this won't wait for blocking writers or readers
 149  */
 150 int btrfs_try_tree_write_lock(struct extent_buffer *eb)
 151 {
 152         if (atomic_read(&eb->blocking_writers) ||
 153             atomic_read(&eb->blocking_readers))
 154                 return 0;
 155         write_lock(&eb->lock);
 156         if (atomic_read(&eb->blocking_writers) ||
 157             atomic_read(&eb->blocking_readers)) {
 158                 write_unlock(&eb->lock);
 159                 return 0;
 160         }
 161         atomic_inc(&eb->write_locks);
 162         atomic_inc(&eb->spinning_writers);
 163         eb->lock_owner = current->pid;
 164         return 1;
 165 }
 166
 167 /*
 168  * drop a spinning read lock
 169  */
 170 void btrfs_tree_read_unlock(struct extent_buffer *eb)
 171 {
 172         if (eb->lock_nested) {
 173                 read_lock(&eb->lock);
 174                 if (eb->lock_nested && current->pid == eb->lock_owner) {
 175                         eb->lock_nested = 0;
 176                         read_unlock(&eb->lock);
 177                         return;
 178                 }
 179                 read_unlock(&eb->lock);
 180         }
 181         btrfs_assert_tree_read_locked(eb);
 182         WARN_ON(atomic_read(&eb->spinning_readers) == 0);
 183         atomic_dec(&eb->spinning_readers);
 184         atomic_dec(&eb->read_locks);
 185         read_unlock(&eb->lock);
 186 }
 187
 188 /*
 189  * drop a blocking read lock
 190  */
 191 void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
 192 {
 193         if (eb->lock_nested) {
 194                 read_lock(&eb->lock);
 195                 if (eb->lock_nested && current->pid == eb->lock_owner) {
 196                         eb->lock_nested = 0;
 197                         read_unlock(&eb->lock);
 198                         return;
 199                 }
 200                 read_unlock(&eb->lock);
 201         }
 202         btrfs_assert_tree_read_locked(eb);
 203         WARN_ON(atomic_read(&eb->blocking_readers) == 0);
 204         if (atomic_dec_and_test(&eb->blocking_readers) &&
 205             waitqueue_active(&eb->read_lock_wq))
 206                 wake_up(&eb->read_lock_wq);
 207         atomic_dec(&eb->read_locks);
 208 }
 209
 210 /*
 211  * take a spinning write lock.  This will wait for both
 212  * blocking readers or writers
 213  */
 214 void btrfs_tree_lock(struct extent_buffer *eb)
 215 {
 216 again:
 217         wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
 218         wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
 219         write_lock(&eb->lock);
 220         if (atomic_read(&eb->blocking_readers)) {
 221                 write_unlock(&eb->lock);
 222                 wait_event(eb->read_lock_wq,
 223                            atomic_read(&eb->blocking_readers) == 0);
 224                 goto again;
 225         }
 226         if (atomic_read(&eb->blocking_writers)) {
 227                 write_unlock(&eb->lock);
 228                 wait_event(eb->write_lock_wq,
 229                            atomic_read(&eb->blocking_writers) == 0);
 230                 goto again;
 231         }
 232         WARN_ON(atomic_read(&eb->spinning_writers));
 233         atomic_inc(&eb->spinning_writers);
 234         atomic_inc(&eb->write_locks);
 235         eb->lock_owner = current->pid;
 236 }
 237
 238 /*
 239  * drop a spinning or a blocking write lock.
 240  */
 241 void btrfs_tree_unlock(struct extent_buffer *eb)
 242 {
 243         int blockers = atomic_read(&eb->blocking_writers);
 244
 245         BUG_ON(blockers > 1);
 246
 247         btrfs_assert_tree_locked(eb);
 248         atomic_dec(&eb->write_locks);
 249
 250         if (blockers) {
 251                 WARN_ON(atomic_read(&eb->spinning_writers));
 252                 atomic_dec(&eb->blocking_writers);
 253                 smp_mb();
 254                 if (waitqueue_active(&eb->write_lock_wq))
 255                         wake_up(&eb->write_lock_wq);
 256         } else {
 257                 WARN_ON(atomic_read(&eb->spinning_writers) != 1);
 258                 atomic_dec(&eb->spinning_writers);
 259                 write_unlock(&eb->lock);
 260         }
 261 }
 262
 263 void btrfs_assert_tree_locked(struct extent_buffer *eb)
 264 {
 265         BUG_ON(!atomic_read(&eb->write_locks));
 266 }
 267
 268 void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
 269 {
 270         BUG_ON(!atomic_read(&eb->read_locks));
 271 }