Re: fio test triggering bad data on ext4

Eric Sandeen
2010-06-18T18:04:47Z

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()

-Eric