ext4: defer saving error info from atomic context

mainline inclusion
from mainline-v5.11-rc1
commit c92dc856848f32781e37b88c1b7f875e274f5efb
category: bugfix
bugzilla: 46758
CVE: NA

-----------------------------------------------

When filesystem inconsistency is detected with group locked, we
currently try to modify superblock to store error there without
blocking. However this can cause superblock checksum failures (or
DIF/DIX failure) when the superblock is just being written out.

Make error handling code just store error information in ext4_sb_info
structure and copy it to on-disk superblock only in ext4_commit_super().
In case of error happening with group locked, we just postpone the
superblock flushing to a workqueue.

[ Added fixup so that s_first_error_* does not get updated after
  the file system is remounted.
  Also added fix for syzbot failure.  - Ted ]

Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20201127113405.26867-8-jack@suse.cz


Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: Hillf Danton <hdanton@sina.com>
Reported-by:  <syzbot+9043030c040ce1849a60@syzkaller.appspotmail.com>

conflicts:
fs/ext4/ext4.h
fs/ext4/super.c

Signed-off-by: Ye Bin <yebin10@huawei.com>
Reviewed-by: zhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>