Re: fio test triggering bad data on ext4

Jens Axboe
2010-06-18T18:14:47Z

On 2010-06-18 20:04, Eric Sandeen wrote:
> Jens Axboe wrote:
>> On 2010-06-18 17:28, Eric Sandeen wrote:
>>> Jens Axboe wrote:
>>>> On 18/06/10 16.59, Eric Sandeen wrote:
>>>>
>>>>> Eric Sandeen wrote:
>>>>>
>>>>>> Jens Axboe wrote:
>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> I was writing a small fio job file to do writes and read verifies on a
>>>>>>> device. It forks 32 processes, each writing randomly to 4 files with a
>>>>>>> block size between 4k and 16k. When it has written 1024 of those blocks,
>>>>>>> it'll verify the oldest 512 of them. Each block is checksummed for every
>>>>>>> 512b. It uses libaio and O_DIRECT.
>>>>>>>
>>>>>>> It works on ext2 and btrfs. I haven't run it to completion yet, but they
>>>>>>> survive 15-20 minutes just fine. ext4 doesn't even go a full minutes
>>>>>>> before this triggers:
>>>>>>>
>>>>>> Jens, can you try XFS too? Since ext3 can't do direct IO to a hole,
>>>>>> (and I'm not sure about btrfs in that regard), ext4 may be most similar
>>>>>> to xfs's behavior on the test ... wondering how it fares.
>>>>>>
>>>>>> Thanks,
>>>>>> -Eric
>>>>>>
>>>>> Actually mingming had a patch for direct-io.c which may be related, I'll
>>>>> test that out.
>>>>>
>>>> OK, I'll try XFS tonight as well.
>>>>
>>>>
>>>>
>>> I haven't been able to reproduce it on ext4 here, yet.
>>>
>>> FWIW here's the patch from mingming:
>>>
>>> When unaligned DIO writes, skip zero out the block if the buffer is marked
>>> unwritten. That means there is an asynconous direct IO (append or fill the hole)
>>> still pending.
>>>
>>> Signed-off-by: Mingming Cao <cmm@us.ibm.com>
>>> ---
>>> fs/direct-io.c | 3 ++-
>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> Index: linux-git/fs/direct-io.c
>>> ===================================================================
>>> --- linux-git.orig/fs/direct-io.c 2010-05-07 15:42:22.855033403 -0700
>>> +++ linux-git/fs/direct-io.c 2010-05-07 15:44:17.695007770 -0700
>>> @@ -740,7 +740,8 @@
>>> struct page *page;
>>>
>>> dio->start_zero_done = 1;
>>> - if (!dio->blkfactor || !buffer_new(&dio->map_bh))
>>> + if (!dio->blkfactor || !buffer_new(&dio->map_bh)
>>> + || buffer_unwritten(&dio->map_bh))
>>> return;
>>>
>>> dio_blocks_per_fs_block = 1 << dio->blkfactor;
>>>
>>>
>>
>> What is this patch against?
>>
>
> Applied to 2.6.32, seems to apply upstream as well.
>
> It hits dio_zero-block()

Irk indeed, I am blind. The patch does not fix it.

--
Jens Axboe