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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>
This commit is contained in:
Miao Xie 2014-02-20 18:08:51 +08:00 committed by Josef Bacik
parent 7813b3db0a
commit 5c902ba622
1 changed files with 10 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
fs/btrfs/tree-log.c
View File

@ -2375,14 +2375,14 @@ static int wait_log_commit(struct btrfs_trans_handle *trans,
&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 @@ static void wait_for_writer(struct btrfs_trans_handle *trans,
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 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
}
/* 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 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
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 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
* 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);