[PATCH] Btrfs: do not backup tree roots when fsync

[Liu Bo <bo.li.liu@oracle.com>]

It doens't make sense to backup tree roots when doing fsync, since
during fsync those tree roots have not been consistent on disk.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
---
 fs/btrfs/disk-io.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 79ac228..a145a88 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3668,7 +3668,14 @@ int write_all_supers(struct btrfs_fs_info *fs_info, int max_mirrors)
 	u64 flags;
 
 	do_barriers = !btrfs_test_opt(fs_info, NOBARRIER);
-	backup_super_roots(fs_info);
+
+	/*
+	 * max_mirrors == 0 indicates we're from commit_transaction,
+	 * not from fsync where the tree roots in fs_info have not
+	 * been consistent on disk.
+	 */
+	if (max_mirrors == 0)
+		backup_super_roots(fs_info);
 
 	sb = fs_info->super_for_commit;
 	dev_item = &sb->dev_item;
-- 
2.9.4