linux-kernel - Re: [PATCH v2 3/3] ext4: fix corruption when online resizing a 1K bigalloc fs

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Message-ID: <20221116115618.bnbnabifqnhvi5ii@quack3>
Date:   Wed, 16 Nov 2022 12:56:18 +0100
From:   Jan Kara <jack@...e.cz>
To:     Baokun Li <libaokun1@...wei.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu,
        adilger.kernel@...ger.ca, jack@...e.cz, ritesh.list@...il.com,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
        yukuai3@...wei.com
Subject: Re: [PATCH v2 3/3] ext4: fix corruption when online resizing a 1K
 bigalloc fs

On Wed 16-11-22 15:28:02, Baokun Li wrote:
> When a backup superblock is updated in update_backups(), the primary
> superblock's offset in the group (that is, sbi->s_sbh->b_blocknr) is used
> as the backup superblock's offset in its group. However, when the block
> size is 1K and bigalloc is enabled, the two offsets are not equal. This
> causes the backup group descriptors to be overwritten by the superblock
> in update_backups(). Moreover, if meta_bg is enabled, the file system will
> be corrupted because this feature uses backup group descriptors.
> 
> To solve this issue, we use a more accurate ext4_group_first_block_no() as
> the offset of the backup superblock in its group.
> 
> Fixes: d77147ff443b ("ext4: add support for online resizing with bigalloc")
> Signed-off-by: Baokun Li <libaokun1@...wei.com>

The patch looks good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
> V1->V2:
>     Replace s_first_data_block with ext4_group_first_block_no() to avoid
>     type warning.(Reported-by: kernel test robot <lkp@...el.com>)
> 
>  fs/ext4/resize.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
> index 32fbfc173571..98e544c2f97d 100644
> --- a/fs/ext4/resize.c
> +++ b/fs/ext4/resize.c
> @@ -1591,8 +1591,8 @@ static int ext4_flex_group_add(struct super_block *sb,
>  		int meta_bg = ext4_has_feature_meta_bg(sb);
>  		sector_t old_gdb = 0;
>  
> -		update_backups(sb, sbi->s_sbh->b_blocknr, (char *)es,
> -			       sizeof(struct ext4_super_block), 0);
> +		update_backups(sb, ext4_group_first_block_no(sb, 0),
> +			       (char *)es, sizeof(struct ext4_super_block), 0);
>  		for (; gdb_num <= gdb_num_end; gdb_num++) {
>  			struct buffer_head *gdb_bh;
>  
> @@ -1803,7 +1803,7 @@ static int ext4_group_extend_no_check(struct super_block *sb,
>  		if (test_opt(sb, DEBUG))
>  			printk(KERN_DEBUG "EXT4-fs: extended group to %llu "
>  			       "blocks\n", ext4_blocks_count(es));
> -		update_backups(sb, EXT4_SB(sb)->s_sbh->b_blocknr,
> +		update_backups(sb, ext4_group_first_block_no(sb, 0),
>  			       (char *)es, sizeof(struct ext4_super_block), 0);
>  	}
>  	return err;
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR