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

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Message-ID: <CAGBYx2YNKEiuRF31CaRiK2ROj_xmVsnL4rcWnoofyziYCkYjpw@mail.gmail.com>
Date:	Tue, 6 Dec 2011 11:08:36 +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]

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.

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
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