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 static 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         if (atomic_read(&eb->blocking_writers)) {
 117                 read_unlock(&eb->lock);
 118                 wait_event(eb->write_lock_wq,
 119                            atomic_read(&eb->blocking_writers) == 0);
 120                 goto again;
 121         }
 122         atomic_inc(&eb->read_locks);
 123         atomic_inc(&eb->spinning_readers);
 124 }
 125
 126 /*
 127  * returns 1 if we get the read lock and 0 if we don't
 128  * this won't wait for blocking writers
 129  */
 130 int btrfs_try_tree_read_lock(struct extent_buffer *eb)
 131 {
 132         if (atomic_read(&eb->blocking_writers))
 133                 return 0;
 134
 135         read_lock(&eb->lock);
 136         if (atomic_read(&eb->blocking_writers)) {
 137                 read_unlock(&eb->lock);
 138                 return 0;
 139         }
 140         atomic_inc(&eb->read_locks);
 141         atomic_inc(&eb->spinning_readers);
 142         return 1;
 143 }
 144
 145 /*
 146  * returns 1 if we get the read lock and 0 if we don't
 147  * this won't wait for blocking writers or readers
 148  */
 149 int btrfs_try_tree_write_lock(struct extent_buffer *eb)
 150 {
 151         if (atomic_read(&eb->blocking_writers) ||
 152             atomic_read(&eb->blocking_readers))
 153                 return 0;
 154         write_lock(&eb->lock);
 155         if (atomic_read(&eb->blocking_writers) ||
 156             atomic_read(&eb->blocking_readers)) {
 157                 write_unlock(&eb->lock);
 158                 return 0;
 159         }
 160         atomic_inc(&eb->write_locks);
 161         atomic_inc(&eb->spinning_writers);
 162         eb->lock_owner = current->pid;
 163         return 1;
 164 }
 165
 166 /*
 167  * drop a spinning read lock
 168  */
 169 void btrfs_tree_read_unlock(struct extent_buffer *eb)
 170 {
 171         if (eb->lock_nested) {
 172                 read_lock(&eb->lock);
 173                 if (eb->lock_nested && current->pid == eb->lock_owner) {
 174                         eb->lock_nested = 0;
 175                         read_unlock(&eb->lock);
 176                         return;
 177                 }
 178                 read_unlock(&eb->lock);
 179         }
 180         btrfs_assert_tree_read_locked(eb);
 181         WARN_ON(atomic_read(&eb->spinning_readers) == 0);
 182         atomic_dec(&eb->spinning_readers);
 183         atomic_dec(&eb->read_locks);
 184         read_unlock(&eb->lock);
 185 }
 186
 187 /*
 188  * drop a blocking read lock
 189  */
 190 void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
 191 {
 192         if (eb->lock_nested) {
 193                 read_lock(&eb->lock);
 194                 if (eb->lock_nested && current->pid == eb->lock_owner) {
 195                         eb->lock_nested = 0;
 196                         read_unlock(&eb->lock);
 197                         return;
 198                 }
 199                 read_unlock(&eb->lock);
 200         }
 201         btrfs_assert_tree_read_locked(eb);
 202         WARN_ON(atomic_read(&eb->blocking_readers) == 0);
 203         if (atomic_dec_and_test(&eb->blocking_readers) &&
 204             waitqueue_active(&eb->read_lock_wq))
 205                 wake_up(&eb->read_lock_wq);
 206         atomic_dec(&eb->read_locks);
 207 }
 208
 209 /*
 210  * take a spinning write lock.  This will wait for both
 211  * blocking readers or writers
 212  */
 213 void btrfs_tree_lock(struct extent_buffer *eb)
 214 {
 215 again:
 216         wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
 217         wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
 218         write_lock(&eb->lock);
 219         if (atomic_read(&eb->blocking_readers)) {
 220                 write_unlock(&eb->lock);
 221                 wait_event(eb->read_lock_wq,
 222                            atomic_read(&eb->blocking_readers) == 0);
 223                 goto again;
 224         }
 225         if (atomic_read(&eb->blocking_writers)) {
 226                 write_unlock(&eb->lock);
 227                 wait_event(eb->write_lock_wq,
 228                            atomic_read(&eb->blocking_writers) == 0);
 229                 goto again;
 230         }
 231         WARN_ON(atomic_read(&eb->spinning_writers));
 232         atomic_inc(&eb->spinning_writers);
 233         atomic_inc(&eb->write_locks);
 234         eb->lock_owner = current->pid;
 235 }
 236
 237 /*
 238  * drop a spinning or a blocking write lock.
 239  */
 240 void btrfs_tree_unlock(struct extent_buffer *eb)
 241 {
 242         int blockers = atomic_read(&eb->blocking_writers);
 243
 244         BUG_ON(blockers > 1);
 245
 246         btrfs_assert_tree_locked(eb);
 247         atomic_dec(&eb->write_locks);
 248
 249         if (blockers) {
 250                 WARN_ON(atomic_read(&eb->spinning_writers));
 251                 atomic_dec(&eb->blocking_writers);
 252                 smp_mb();
 253                 if (waitqueue_active(&eb->write_lock_wq))
 254                         wake_up(&eb->write_lock_wq);
 255         } else {
 256                 WARN_ON(atomic_read(&eb->spinning_writers) != 1);
 257                 atomic_dec(&eb->spinning_writers);
 258                 write_unlock(&eb->lock);
 259         }
 260 }
 261
 262 void btrfs_assert_tree_locked(struct extent_buffer *eb)
 263 {
 264         BUG_ON(!atomic_read(&eb->write_locks));
 265 }
 266
 267 static void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
 268 {
 269         BUG_ON(!atomic_read(&eb->read_locks));
 270 }