ext4: fix e2fsprogs checksum failure for mounted filesystem

Commit 81414b4dd48 ("ext4: remove redundant sb checksum
recomputation") removed checksum recalculation after updating
superblock free space / inode counters in ext4_fill_super() based on
the fact that we will recalculate the checksum on superblock
writeout.

That is correct assumption but until the writeout happens (which can
take a long time) the checksum is incorrect in the buffer cache and if
programs such as tune2fs or resize2fs is called shortly after a file
system is mounted can fail.  So return back the checksum recalculation
and add a comment explaining why.

Fixes: 81414b4dd48f ("ext4: remove redundant sb checksum recomputation")
Cc: stable@kernel.org
Reported-by: Boyang Xue <bxue@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Link: https://lore.kernel.org/r/20210812124737.21981-1-jack@suse.cz

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index dfa09a277b56fb4a1add7b5c28d8e75030c65023..970013c93d3ea243bed45a0f49a963d1f12472e9 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5032,6 +5032,14 @@ no_journal:
                err = percpu_counter_init(&sbi->s_freeinodes_counter, freei,
                                          GFP_KERNEL);
        }
+       /*
+        * Update the checksum after updating free space/inode
+        * counters.  Otherwise the superblock can have an incorrect
+        * checksum in the buffer cache until it is written out and
+        * e2fsprogs programs trying to open a file system immediately
+        * after it is mounted can fail.
+        */
+       ext4_superblock_csum_set(sb);
        if (!err)
                err = percpu_counter_init(&sbi->s_dirs_counter,
                                          ext4_count_dirs(sb), GFP_KERNEL);