ext4: recalucate superblock checksum after updating free blocks/inodes
authorTheodore Ts'o <tytso@mit.edu>
Sat, 1 Sep 2018 18:42:14 +0000 (14:42 -0400)
committerTheodore Ts'o <tytso@mit.edu>
Sat, 1 Sep 2018 18:42:14 +0000 (14:42 -0400)
commit4274f516d4bc50648a4d97e4f67ecbd7b65cde4a
treeca5f67e0132c8969e20bf988508b04d24ee9aabb
parentbcd8e91f98c156f4b1ebcfacae675f9cfd962441
ext4: recalucate superblock checksum after updating free blocks/inodes

When mounting the superblock, ext4_fill_super() calculates the free
blocks and free inodes and stores them in the superblock.  It's not
strictly necessary, since we don't use them any more, but it's nice to
keep them roughly aligned to reality.

Since it's not critical for file system correctness, the code doesn't
call ext4_commit_super().  The problem is that it's in
ext4_commit_super() that we recalculate the superblock checksum.  So
if we're not going to call ext4_commit_super(), we need to call
ext4_superblock_csum_set() to make sure the superblock checksum is
consistent.

Most of the time, this doesn't matter, since we end up calling
ext4_commit_super() very soon thereafter, and definitely by the time
the file system is unmounted.  However, it doesn't work in this
sequence:

mke2fs -Fq -t ext4 /dev/vdc 128M
mount /dev/vdc /vdc
cp xfstests/git-versions /vdc
godown /vdc
umount /vdc
mount /dev/vdc
tune2fs -l /dev/vdc

With this commit, the "tune2fs -l" no longer fails.

Reported-by: Chengguang Xu <cgxu519@gmx.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
fs/ext4/super.c