ext4: fix memory leak in ext4_fill_super

mainline inclusion
from mainline-5.14
commit	618f003199c6188e01472b03cdbba227f1dc5f24
category: bugfix
bugzilla: 167360
CVE: NA

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

static int kthread(void *_create) will return -ENOMEM
or -EINTR in case of internal failure or
kthread_stop() call happens before threadfn call.

To prevent fancy error checking and make code
more straightforward we moved all cleanup code out
of kmmpd threadfn.

Also, dropped struct mmpd_data at all. Now struct super_block
is a threadfn data and struct buffer_head embedded into
struct ext4_sb_info.

Reported-by:  <syzbot+d9e482e303930fa4f6ff@syzkaller.appspotmail.com>
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Link: https://lore.kernel.org/r/20210430185046.15742-1-paskripkin@gmail.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>

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

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Ya...