btrfs: sync ioctl, handle errors after transaction start

The version merged to 3.19 did not handle errors from start_trancaction
and could pass an invalid pointer to commit_transaction.

Fixes: 6b5fe46dfa52441f ("btrfs: do commit in sync_fs if there are pending changes")
Reported-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 60f7cbe815e9..c86fb5438454 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1001,9 +1001,9 @@ int btrfs_sync_fs(struct super_block *sb, int wait)
                         if (fs_info->pending_changes == 0)
                                 return 0;
                         trans = btrfs_start_transaction(root, 0);
-                } else {
-                        return PTR_ERR(trans);
                 }
+                if (IS_ERR(trans))
+                        return PTR_ERR(trans);
         }
         return btrfs_commit_transaction(trans, root);
 }