Btrfs: use ACCESS_ONCE to prevent the optimize accesses to ->last_trans_log_full_commit
->last_trans_log_full_commit may be changed by the other tasks without lock,
so we need prevent the compiler from the optimize access just like
tmp = fs_info->last_trans_log_full_commit
if (tmp == ...)
...
<do something>
if (tmp == ...)
...
In fact, we need get the new value of ->last_trans_log_full_commit during
the second access. Fix it by ACCESS_ONCE().
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 7c449c6..5a4e10b 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -2375,14 +2375,14 @@
&wait, TASK_UNINTERRUPTIBLE);
mutex_unlock(&root->log_mutex);
- if (root->fs_info->last_trans_log_full_commit !=
+ if (ACCESS_ONCE(root->fs_info->last_trans_log_full_commit) !=
trans->transid && root->log_transid < transid + 2 &&
atomic_read(&root->log_commit[index]))
schedule();
finish_wait(&root->log_commit_wait[index], &wait);
mutex_lock(&root->log_mutex);
- } while (root->fs_info->last_trans_log_full_commit !=
+ } while (ACCESS_ONCE(root->fs_info->last_trans_log_full_commit) !=
trans->transid && root->log_transid < transid + 2 &&
atomic_read(&root->log_commit[index]));
return 0;
@@ -2392,12 +2392,12 @@
struct btrfs_root *root)
{
DEFINE_WAIT(wait);
- while (root->fs_info->last_trans_log_full_commit !=
+ while (ACCESS_ONCE(root->fs_info->last_trans_log_full_commit) !=
trans->transid && atomic_read(&root->log_writers)) {
prepare_to_wait(&root->log_writer_wait,
&wait, TASK_UNINTERRUPTIBLE);
mutex_unlock(&root->log_mutex);
- if (root->fs_info->last_trans_log_full_commit !=
+ if (ACCESS_ONCE(root->fs_info->last_trans_log_full_commit) !=
trans->transid && atomic_read(&root->log_writers))
schedule();
mutex_lock(&root->log_mutex);
@@ -2456,7 +2456,8 @@
}
/* bail out if we need to do a full commit */
- if (root->fs_info->last_trans_log_full_commit == trans->transid) {
+ if (ACCESS_ONCE(root->fs_info->last_trans_log_full_commit) ==
+ trans->transid) {
ret = -EAGAIN;
btrfs_free_logged_extents(log, log_transid);
mutex_unlock(&root->log_mutex);
@@ -2515,7 +2516,8 @@
mutex_unlock(&log_root_tree->log_mutex);
goto out;
}
- root->fs_info->last_trans_log_full_commit = trans->transid;
+ ACCESS_ONCE(root->fs_info->last_trans_log_full_commit) =
+ trans->transid;
btrfs_wait_marked_extents(log, &log->dirty_log_pages, mark);
btrfs_free_logged_extents(log, log_transid);
mutex_unlock(&log_root_tree->log_mutex);
@@ -2547,7 +2549,8 @@
* now that we've moved on to the tree of log tree roots,
* check the full commit flag again
*/
- if (root->fs_info->last_trans_log_full_commit == trans->transid) {
+ if (ACCESS_ONCE(root->fs_info->last_trans_log_full_commit) ==
+ trans->transid) {
blk_finish_plug(&plug);
btrfs_wait_marked_extents(log, &log->dirty_log_pages, mark);
btrfs_free_logged_extents(log, log_transid);