linux-ext4 - Re: what happened with dccaf33fa37 "ext4: flush any pending end

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Message-ID: <CAFgt=MCXRzLx+s1mthr1oD=Pj=HQ5kxnOdbtX8Q9=wSeZ41u2w@mail.gmail.com>
Date:	Mon, 19 Mar 2012 10:10:11 -0700
From:	Jiaying Zhang <jiayingz@...gle.com>
To:	Michael Tokarev <mjt@....msk.ru>, Theodore Tso <tytso@...gle.com>
Cc:	gregkh@...uxfoundation.org, stable@...nel.org,
	linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>,
	Jan Kara <jack@...e.cz>
Subject: Re: what happened with dccaf33fa37 "ext4: flush any pending end_io
 requests before DIO" for 3.0?

On Mon, Mar 19, 2012 at 9:42 AM, Jan Kara <jack@...e.cz> wrote:
> On Sat 17-03-12 13:31:30, Michael Tokarev wrote:
>> Ping?
>>
>> Maybe just a one-line reply isn't THAT difficult?
Sorry for the slow response. I am not sure what happened to this patch.
Ted, do you know what we need to do to get this patch to the
stable release?

Jiaying

>>
>> We've a data corruption bug in current longterm stable kernel
>> series which is known and has a fix and tagged for -stable for
>> over half a year already...
>  Greg, any idea why this patch was not included?
>
>                                                        Honza
>
>> On 28.02.2012 15:42, Michael Tokarev wrote:
>> > Is there something wrong with my question?  I asked it 1.5 months ago...
>> >
>> > Meanwhile, we're using this patch on our database server since
>> > Aug-2011, and it appears to work correctly - direct and buffered
>> > I/O works together without surprizes.  Without this patch, I see
>> > unexpected results.
>> >
>> > Thanks,
>> >
>> > /mjt
>> >
>> > On 01.12.2011 00:38, Michael Tokarev wrote:
>> >> Hello.
>> >>
>> >> Back in August 2011, a commit has been tagged to be included
>> >> into stable, this one:
>> >>
>> >> commit dccaf33fa37a1bc5d651baeb3bfeb6becb86597b
>> >> Author: Jiaying Zhang <jiayingz@...gle.com>
>> >> Date:   Fri Aug 19 19:13:32 2011 -0400
>> >>
>> >>     ext4: flush any pending end_io requests before DIO reads w/dioread_nolock
>> >>
>> >>     There is a race between ext4 buffer write and direct_IO read with
>> >>     dioread_nolock mount option enabled. The problem is that we clear
>> >>     PageWriteback flag during end_io time but will do
>> >>     uninitialized-to-initialized extent conversion later with dioread_nolock.
>> >>     If an O_direct read request comes in during this period, ext4 will return
>> >>     zero instead of the recently written data.
>> >>
>> >>     This patch checks whether there are any pending uninitialized-to-initialized
>> >>     extent conversion requests before doing O_direct read to close the race.
>> >>     Note that this is just a bandaid fix. The fundamental issue is that we
>> >>     clear PageWriteback flag before we really complete an IO, which is
>> >>     problem-prone. To fix the fundamental issue, we may need to implement an
>> >>     extent tree cache that we can use to look up pending to-be-converted extents.
>> >>
>> >>     Signed-off-by: Jiaying Zhang <jiayingz@...gle.com>
>> >>     Signed-off-by: "Theodore Ts'o" <tytso@....edu>
>> >>     Cc: stable@...nel.org
>> >>
>> >>
>> >> There was one more ext4 commit at that time, which made its way into
>> >> stable but this one did not.
>> >>
>> >> I wonder if the reason for that was the fact that it needed a small
>> >> "backport" for 3.0, since in 3.1+ the code has been moved into another
>> >> file, and the context is slightly different.  In that case, attached
>> >> is the "backport" which we use with 3.0.x since that time.
>> >>
>> >> Thanks!
>> >>
>> >> /mjt
>> >
>>
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