ext4: save error info to sb through journal if available

ext4: save error info to sb through journal if available

If journalling is still working at the moment we get to writing error
information to the superblock we cannot write directly to the superblock
as such write could race with journalled update of the superblock and
cause journal checksum failures, writing inconsistent information to the
journal or other problems. We cannot journal the superblock directly
from the error handling functions as we are running in uncertain context
and could deadlock so just punt journalled superblock update to a
workqueue.

Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20201216101844.22917-5-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>