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

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Date:	Fri, 18 Jun 2010 13:04:31 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Jens Axboe <jaxboe@...ionio.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

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()

-Eric
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