Re: [PATCH] ext4: fix bad checksum after online resize

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, Nov 04, 2022 at 04:35:53PM +0800, Baokun Li wrote:
> When online resizing is performed twice consecutively, the error message
> "Superblock checksum does not match superblock" is displayed for the
> second time. Here's the reproducer:
> 
> 	mkfs.ext4 -F /dev/sdb 100M
> 	mount /dev/sdb /tmp/test
> 	resize2fs /dev/sdb 5G
> 	resize2fs /dev/sdb 6G
> 
> To solve this issue, we moved the update of the checksum after the
> es->s_overhead_clusters is updated.
> 
> Fixes: 026d0d27c488 ("ext4: reduce computation of overhead during resize")
> Fixes: de394a86658f ("ext4: update s_overhead_clusters in the superblock during an on-line resize")
> Signed-off-by: Baokun Li <libaokun1@huawei.com>

Yep, that looks correct.  Sort of a pity that the checksum computation
isn't quite as automatic as it is in other filesystems, but that's my
fault... :/

Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
>  fs/ext4/resize.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
> index 6dfe9ccae0c5..32fbfc173571 100644
> --- a/fs/ext4/resize.c
> +++ b/fs/ext4/resize.c
> @@ -1471,8 +1471,6 @@ static void ext4_update_super(struct super_block *sb,
>  	 * active. */
>  	ext4_r_blocks_count_set(es, ext4_r_blocks_count(es) +
>  				reserved_blocks);
> -	ext4_superblock_csum_set(sb);
> -	unlock_buffer(sbi->s_sbh);
>  
>  	/* Update the free space counts */
>  	percpu_counter_add(&sbi->s_freeclusters_counter,
> @@ -1508,6 +1506,8 @@ static void ext4_update_super(struct super_block *sb,
>  		ext4_calculate_overhead(sb);
>  	es->s_overhead_clusters = cpu_to_le32(sbi->s_overhead);
>  
> +	ext4_superblock_csum_set(sb);
> +	unlock_buffer(sbi->s_sbh);
>  	if (test_opt(sb, DEBUG))
>  		printk(KERN_DEBUG "EXT4-fs: added group %u:"
>  		       "%llu blocks(%llu free %llu reserved)\n", flex_gd->count,
> -- 
> 2.31.1
>