Re: [PATCH] ext4: Fix incorrect group count in ext4_fill_super error message

From: Andreas Dilger <adilger@dilger.ca>
To: Josh Triplett <josh@joshtriplett.org>
Cc: linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org,
	Theodore Ts'o <tytso@mit.edu>,
	Andreas Dilger <adilger.kernel@dilger.ca>
Subject: Re: [PATCH] ext4: Fix incorrect group count in ext4_fill_super error message
Date: Sat, 28 Mar 2020 17:07:55 -0600	[thread overview]
Message-ID: <04E7F659-18B0-4CD2-8DE9-F69310BC3B06@dilger.ca> (raw)
In-Reply-To: <8b957cd1513fcc4550fe675c10bcce2175c33a49.1585431964.git.josh@joshtriplett.org>

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On Mar 28, 2020, at 3:54 PM, Josh Triplett <josh@joshtriplett.org> wrote:
> 
> ext4_fill_super doublechecks the number of groups before mounting; if
> that check fails, the resulting error message prints the group count
> from the ext4_sb_info sbi, which hasn't been set yet. Print the freshly
> computed group count instead (which at that point has just been computed
> in "blocks_count").
> 
> Signed-off-by: Josh Triplett <josh@joshtriplett.org>
> Fixes: 4ec1102813798 ("ext4: Add sanity checks for the superblock before mounting the filesystem")

Modulo the compiler warning pointed out by kbuild test robot, I think the
patch is correct, but was definitely confusing to read within the shown
context, since "blocks_count" definitely doesn't seem to be "groups count"
(it *is* the "groups count", but is just used as a temporary variable).

Reviewed-by: Andreas Dilger <adilger@dilger.ca>

> ---
> fs/ext4/super.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 0c7c4adb664e..7f5f37653a03 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -4288,7 +4288,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> 	if (blocks_count > ((uint64_t)1<<32) - EXT4_DESC_PER_BLOCK(sb)) {
> 		ext4_msg(sb, KERN_WARNING, "groups count too large: %u "
> 		       "(block count %llu, first data block %u, "
> -		       "blocks per group %lu)", sbi->s_groups_count,
> +		       "blocks per group %lu)", blocks_count,
> 		       ext4_blocks_count(es),
> 		       le32_to_cpu(es->s_first_data_block),
> 		       EXT4_BLOCKS_PER_GROUP(sb));
> --
> 2.26.0

Cheers, Andreas

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