linux-ext4 - Re: Bug with "fix partial page writes" [3.2-rc regression]

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Date:	Tue, 6 Dec 2011 11:20:10 +0800
From:	Yongqiang Yang <xiaoqiangnk@...il.com>
To:	Allison Henderson <achender@...ux.vnet.ibm.com>
Cc:	Hugh Dickins <hughd@...gle.com>, "Ted Ts'o" <tytso@....edu>,
	Curt Wohlgemuth <curtw@...gle.com>,
	Surbhi Palande <csurbhi@...il.com>,
	Rafael Wysocki <rjw@...k.pl>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Bug with "fix partial page writes" [3.2-rc regression]

On Tue, Dec 6, 2011 at 11:08 AM, Yongqiang Yang <xiaoqiangnk@...il.com> wrote:
> Hi Allison,
>
> I noticed another problem which has nothing to do with punching hole.
>  __block_write_begin does not zero buffers beyond EOF.(I guess you
> tried to zero them in your code, am I right? )  When users mapread
> beyond EOF,  users get non-zero data.  I am not sure zero or non-zero
> data should be, but fsx thinks they should be zero data and reports an
> error.
>
> It I understand the problem right, it happens more often with punch hole.
Strange!   filemap_fault should have handled the case.

Yongqiang.
>
> Yongqiang.
> On Tue, Dec 6, 2011 at 9:40 AM, Allison Henderson
> <achender@...ux.vnet.ibm.com> wrote:
>> On 12/05/2011 04:38 PM, Hugh Dickins wrote:
>>>
>>> On Mon, 21 Nov 2011, Hugh Dickins wrote:
>>>>
>>>> On Mon, 21 Nov 2011, Ted Ts'o wrote:
>>>>>
>>>>> On Sun, Nov 20, 2011 at 12:59:10PM -0800, Hugh Dickins wrote:
>>>>>>
>>>>>> On Tue, 8 Nov 2011, Curt Wohlgemuth wrote:
>>>>>> It appears that there's a bug with this patch:
>>>
>>>
>>> This has been outstanding for a month now, and we've heard no progress:
>>> please revert commit 02fac1297eb3 "ext4: fix partial page writes" for rc5.
>>>
>>> The problems appear on a 1k-blocksize filesystem under memory pressure:
>>> the hunk in ext4_da_write_end() causes oops, because it's playing with
>>> a page after generic_write_end() dropped our last reference to it; and
>>> backing out the hunk in ext4_da_write_begin() is then found to stop
>>> rare data corruption seen when kbuilding.
>>>
>>> Although I earlier reported that backing out the patch caused an fsx
>>> test to fail earlier, I've since found great variation in how soon it
>>> fails, and seen it fail just as quickly with 02fac1297eb3 still in.
>>> I also reported that I had to go back to 2.6.38 for fsx not to fail
>>> under memory pressure: you won't be surprised that that turned out to
>>> be because 2.6.38 defaults nomblk_io_submit but 2.6.39 mblk_io_submit.
>>>
>>> Thanks,
>>> Hugh
>>>
>>
>>
>> Hi there,
>>
>> Have you tried Yongqiang's patch "[PATCH 1/2] ext4: let mpage_submit_io
>> works well when blocksize < pagesize" ?  I have tried it and it does seem to
>> help, but I am still running into some failures that I am trying to debug,
>> but let please let us know if it helps the issues that you are seeing.  Thx!
>>
>> Allison Henderson
>>
>
>
>
> --
> Best Wishes
> Yongqiang Yang



-- 
Best Wishes
Yongqiang Yang
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