Commit 5c902ba6 authored by Miao Xie's avatar Miao Xie Committed by Josef Bacik
Browse files

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: default avatarMiao Xie <miaox@cn.fujitsu.com>
Signed-off-by: default avatarJosef Bacik <jbacik@fb.com>
parent 7813b3db

fs/btrfs/tree-log.c

+10 −7
Original line number Original line Diff line number Diff line
@@ -2375,14 +2375,14 @@ static int wait_log_commit(struct btrfs_trans_handle *trans, 
				&wait, TASK_UNINTERRUPTIBLE);

				&wait, TASK_UNINTERRUPTIBLE);

		mutex_unlock(&root->log_mutex);

		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 &&

		    trans->transid && root->log_transid < transid + 2 &&

		    atomic_read(&root->log_commit[index]))

		    atomic_read(&root->log_commit[index]))

			schedule();

			schedule();





		finish_wait(&root->log_commit_wait[index], &wait);

		finish_wait(&root->log_commit_wait[index], &wait);

		mutex_lock(&root->log_mutex);

		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 &&

		 trans->transid && root->log_transid < transid + 2 &&

		 atomic_read(&root->log_commit[index]));

		 atomic_read(&root->log_commit[index]));

	return 0;

	return 0;
@@ -2392,12 +2392,12 @@ static void wait_for_writer(struct btrfs_trans_handle *trans, 
			    struct btrfs_root *root)

			    struct btrfs_root *root)

{

{

	DEFINE_WAIT(wait);

	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)) {

	       trans->transid && atomic_read(&root->log_writers)) {

		prepare_to_wait(&root->log_writer_wait,

		prepare_to_wait(&root->log_writer_wait,

				&wait, TASK_UNINTERRUPTIBLE);

				&wait, TASK_UNINTERRUPTIBLE);

		mutex_unlock(&root->log_mutex);

		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))

		    trans->transid && atomic_read(&root->log_writers))

			schedule();

			schedule();

		mutex_lock(&root->log_mutex);

		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 */

	/* 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;

		ret = -EAGAIN;

		btrfs_free_logged_extents(log, log_transid);

		btrfs_free_logged_extents(log, log_transid);

		mutex_unlock(&root->log_mutex);

		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);

			mutex_unlock(&log_root_tree->log_mutex);

			goto out;

			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_wait_marked_extents(log, &log->dirty_log_pages, mark);

		btrfs_free_logged_extents(log, log_transid);

		btrfs_free_logged_extents(log, log_transid);

		mutex_unlock(&log_root_tree->log_mutex);

		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,

	 * now that we've moved on to the tree of log tree roots,

	 * check the full commit flag again

	 * 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);

		blk_finish_plug(&plug);

		btrfs_wait_marked_extents(log, &log->dirty_log_pages, mark);

		btrfs_wait_marked_extents(log, &log->dirty_log_pages, mark);

		btrfs_free_logged_extents(log, log_transid);

		btrfs_free_logged_extents(log, log_transid);

CRA Git | Maintained and supported by SUSTech CRA and CCSE