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

[yebin <yebin10@huawei.com>]

On 2022/3/21 19:37, Jan Kara wrote:
> 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@huawei.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

'ext4_finish_bio' already call 'mapping_set_error' set mapping error , I think fsync
and sync_filesystem can report IO error.

static inline void mapping_set_error(struct address_space *mapping, int error)
{
         if (likely(!error))
                 return;

         /* Record in wb_err for checkers using errseq_t based tracking */
         __filemap_set_wb_err(mapping, error);

         /* Record it in superblock */
         if (mapping->host)
                 errseq_set(&mapping->host->i_sb->s_wb_err, error);

         /* Record it in flags for now, for legacy callers */
         if (error == -ENOSPC)
                 set_bit(AS_ENOSPC, &mapping->flags);
         else
                 set_bit(AS_EIO, &mapping->flags);
}