[kernel-5.11 regression] tune2fs fails after shutdown

[Boyang Xue <bxue@xxxxxxxxxx>]

Hi,

kernel commit

4274f516d4bc ext4: recalucate superblock checksum after updating free
blocks/inodes

had been reverted by

81414b4dd48 ext4: remove redundant sb checksum recomputation

since kernel-5.11-rc1. As a result, the original reproducer fails again.

Reproducer:
```
mkdir mntpt
fallocate -l 256M mntpt.img
mkfs.ext4 -Fq -t ext4 mntpt.img 128M
LPDEV=$(losetup -f --show mntpt.img)
mount "$LPDEV" mntpt
cp /proc/version mntpt/
./godown mntpt # godown program attached.
umount mntpt
mount "$LPDEV" mntpt
tune2fs -l "$LPDEV"
```

tune2fs fails with
```
tune2fs 1.46.2 (28-Feb-2021)
tune2fs: Superblock checksum does not match superblock while trying to
open /dev/loop0
Couldn't find valid filesystem superblock.
```

Tested on e2fsprogs-1.46.2 + kernel-5.14.0-0.rc3.29. I think it's a
regression. If this is the case, can we fix it again please?

Thanks,
Boyang

Attachment: godown.c
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