linux-ext4 - Re: [PATCH -next] ext4: Fix symlink file size not match to file content

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Date:   Mon, 21 Mar 2022 12:37:03 +0100
From:   Jan Kara <jack@...e.cz>
To:     Ye Bin <yebin10@...wei.com>
Cc:     tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        jack@...e.cz, lczerner@...hat.com
Subject: Re: [PATCH -next] ext4: Fix symlink file size not match to file
 content

On Mon 21-03-22 19:34:08, Ye Bin wrote:
> We got issue as follows:
> [home]# fsck.ext4  -fn  ram0yb
> e2fsck 1.45.6 (20-Mar-2020)
> Pass 1: Checking inodes, blocks, and sizes
> Pass 2: Checking directory structure
> Symlink /p3/d14/d1a/l3d (inode #3494) is invalid.
> Clear? no
> Entry 'l3d' in /p3/d14/d1a (3383) has an incorrect filetype (was 7, should be 0).
> Fix? no
> 
> As symlink file size not match to file content. If symlink data block
> writback failed, will call ext4_finish_bio to end io. In this path don't
> mark buffer error. When umount do checkpoint can't detect buffer error,
> then will cleanup jounral. Actually, correct data maybe in journal area.
> To solve this issue, mark buffer error when detect bio error in
> ext4_finish_bio.

Thanks for the patch! Let me rephrase the text a bit:

As the symlink file size does not match the file content. If the writeback
of the symlink data block failed, ext4_finish_bio() handles the end of IO.
However this function fails to mark the buffer with BH_write_io_error and
so when unmount does journal checkpoint it cannot detect the writeback
error and will cleanup the journal. Thus we've lost the correct data in the
journal area. To solve this issue, mark the buffer as BH_write_io_error in
ext4_finish_bio().

> Signed-off-by: Ye Bin <yebin10@...wei.com>
> ---
>  fs/ext4/page-io.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
> index 495ce59fb4ad..14695e2b5042 100644
> --- a/fs/ext4/page-io.c
> +++ b/fs/ext4/page-io.c
> @@ -134,8 +134,10 @@ static void ext4_finish_bio(struct bio *bio)
>  				continue;
>  			}
>  			clear_buffer_async_write(bh);
> -			if (bio->bi_status)
> +			if (bio->bi_status) {
> +				set_buffer_write_io_error(bh);

Why don't you use mark_buffer_write_io_error()? It will also update other IO
error counters properly so that e.g. fsync(2) or sync_filesystem() can properly
report IO error etc. Granted we'll abort the journal in response to
checkpointing error so the failure will be hard to miss anyway but still
:).

								Honza

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