[PATCH] btrfs: log message when rw remount is attempted with unclean tree-log

[David Sterba <dsterba@suse.com>]

A remount to a read-write filesystem is not safe when there's tree-log
to be replayed. Files that could be opened until now might be affected
by the changes in the tree-log.

A regular mount is needed to replay the log so the filesystem presents
the consistent view with the pending changes included.

CC: stable@vger.kernel.org # 4.4+
Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/super.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 580ba7db67e5..a2554c651548 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1834,6 +1834,8 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
 		}
 
 		if (btrfs_super_log_root(fs_info->super_copy) != 0) {
+			btrfs_warn(f_info,
+		"mount required to replay tree-log, cannot remount read-write");
 			ret = -EINVAL;
 			goto restore;
 		}
-- 
2.24.0