ext4: ignore journal checksum on remount; don't fail

commit 2d5b86e048780c5efa7f7d9708815555919e7b05 upstream.

As of v3.18, ext4 started rejecting a remount which changes the
journal_checksum option.

Prior to that, it was simply ignored; the problem here is that
if someone has this in their fstab for the root fs, now the box
fails to boot properly, because remount of root with the new options
will fail, and the box proceeds with a readonly root.

I think it is a little nicer behavior to accept the option, but
warn that it's being ignored, rather than failing the mount,
but that might be a subjective matter...

Reported-by: Cónräd <conradsand.arma@gmail.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: Josh Boyer <jwboyer@fedoraproject.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 2c9e6864abd932f007d107c65615ad440cd56f2c..fc7391e14c2a0339cb45b39691225bd6b8e20b06 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4849,9 +4849,8 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
        if ((old_opts.s_mount_opt & EXT4_MOUNT_JOURNAL_CHECKSUM) ^
            test_opt(sb, JOURNAL_CHECKSUM)) {
                ext4_msg(sb, KERN_ERR, "changing journal_checksum "
-                        "during remount not supported");
-               err = -EINVAL;
-               goto restore_opts;
+                        "during remount not supported; ignoring");
+               sbi->s_mount_opt ^= EXT4_MOUNT_JOURNAL_CHECKSUM;
        }
 
        if (test_opt(sb, DATA_FLAGS) == EXT4_MOUNT_JOURNAL_DATA) {