linux-ext4 - Re: [PATCH] ext4: fix check to prevent false positive report of incorrect used inodes

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Date:   Mon, 29 Mar 2021 16:26:31 +0200
From:   Jan Kara <jack@...e.cz>
To:     Zhang Yi <yi.zhang@...wei.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu,
        adilger.kernel@...ger.ca, jack@...e.cz
Subject: Re: [PATCH] ext4: fix check to prevent false positive report of
 incorrect used inodes

On Mon 29-03-21 14:19:55, Zhang Yi wrote:
> Commit <50122847007> ("ext4: fix check to prevent initializing reserved
> inodes") check the block group zero and prevent initializing reserved
> inodes. But in some special cases, the reserved inode may not all belong
> to the group zero, it may exist into the second group if we format
> filesystem below.
> 
>   mkfs.ext4 -b 4096 -g 8192 -N 1024 -I 4096 /dev/sda
> 
> So, it will end up triggering a false positive report of a corrupted
> file system. This patch fix it by avoid check reserved inodes if no free
> inode blocks will be zeroed.
> 
> Fixes: 50122847007 ("ext4: fix check to prevent initializing reserved inodes")
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>

Thanks! The patch looks correct but maybe the code can be made more
comprehensible like I suggest below?

> @@ -1543,22 +1544,25 @@ int ext4_init_inode_table(struct super_block *sb, ext4_group_t group,
>  	 * used inodes so we need to skip blocks with used inodes in
>  	 * inode table.
>  	 */
> -	if (!(gdp->bg_flags & cpu_to_le16(EXT4_BG_INODE_UNINIT)))
> -		used_blks = DIV_ROUND_UP((EXT4_INODES_PER_GROUP(sb) -
> -			    ext4_itable_unused_count(sb, gdp)),
> -			    sbi->s_inodes_per_block);
> -
> -	if ((used_blks < 0) || (used_blks > sbi->s_itb_per_group) ||
> -	    ((group == 0) && ((EXT4_INODES_PER_GROUP(sb) -
> -			       ext4_itable_unused_count(sb, gdp)) <
> -			      EXT4_FIRST_INO(sb)))) {
> -		ext4_error(sb, "Something is wrong with group %u: "
> -			   "used itable blocks: %d; "
> -			   "itable unused count: %u",
> -			   group, used_blks,
> -			   ext4_itable_unused_count(sb, gdp));
> -		ret = 1;
> -		goto err_out;
> +	if (!(gdp->bg_flags & cpu_to_le16(EXT4_BG_INODE_UNINIT))) {
> +		used_inos = EXT4_INODES_PER_GROUP(sb) -
> +			    ext4_itable_unused_count(sb, gdp);
> +		used_blks = DIV_ROUND_UP(used_inos, sbi->s_inodes_per_block);
> +
> +		if (used_blks >= 0 && used_blks <= sbi->s_itb_per_group)
> +			used_inos += group * EXT4_INODES_PER_GROUP(sb);

Maybe if would be more comprehensible like:

		/* Bogus inode unused count? */
		if (used_blks < 0 || used_blks > sbi->s_itb_per_group) {
			ext4_error(...);
			ret = 1;
			goto err_out;
		}

		used_inos += EXT4_INODES_PER_GROUP(sb);
		/*
		 * Are there some uninitialized inodes in the inode table
		 * before the first normal inode?
		 */
		if (used_blks != sbi->s_itb_per_group &&
		    used_inos < EXT4_FIRST_INO(sb)) {
			ext4_error(...);
			ret = 1;
			goto err_out;
		}
> +
> +		if ((used_blks < 0) || (used_blks > sbi->s_itb_per_group) ||
> +		    ((used_blks != sbi->s_itb_per_group) &&
> +		     (used_inos < EXT4_FIRST_INO(sb)))) {
> +			ext4_error(sb, "Something is wrong with group %u: "
> +				   "used itable blocks: %d; "
> +				   "itable unused count: %u",
> +				   group, used_blks,
> +				   ext4_itable_unused_count(sb, gdp));
> +			ret = 1;
> +			goto err_out;
> +		}
>  	}

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR