linux-ext4 - Re: fio test triggering bad data on ext4

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Date:	Fri, 18 Jun 2010 20:14:46 +0200
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Eric Sandeen <sandeen@...hat.com>
CC:	"tytso@....edu" <tytso@....edu>,
	"adilger@....com" <adilger@....com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: fio test triggering bad data on ext4

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@...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

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