Commit 4274f516 authored Sep 01, 2018 by Theodore Ts'o

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

parent bcd8e91f

fs/ext4/super.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -4378,11 +4378,13 @@ no_journal:
		block = ext4_count_free_clusters(sb);
		ext4_free_blocks_count_set(sbi->s_es,
		EXT4_C2B(sbi, block));
		ext4_superblock_csum_set(sb);
		err = percpu_counter_init(&sbi->s_freeclusters_counter, block,
		GFP_KERNEL);
		if (!err) {
		unsigned long freei = ext4_count_free_inodes(sb);
		sbi->s_es->s_free_inodes_count = cpu_to_le32(freei);
		ext4_superblock_csum_set(sb);
		err = percpu_counter_init(&sbi->s_freeinodes_counter, freei,
		GFP_KERNEL);
		}

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