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Date:	Mon, 15 Aug 2011 10:36:21 +0800
From:	Tao Ma <>
To:	Michael Tokarev <>
	Jan Kara <>
Subject: Re: DIO process stuck apparently due to dioread_nolock (3.0)

On 08/15/2011 05:07 AM, Michael Tokarev wrote:
> 15.08.2011 00:57, Michael Tokarev пишет:
>> 13.08.2011 20:02, Tao Ma wrote:
>>> From: Tao Ma <>
>>> Hi Michael,
>>> 	could you please check whether this patch work for you?
>> With this patch applied to 3.0.1 I can't trigger the issue anymore,
>> after several attempts -- the system just works as it shold be.
>> I'm not sure this is the right fix or it's just my testcase isn't
>> as good as it can be... ;)
Thanks for the test.
> Well, I found a way to trigger data corruption with this patch
> applied.  I guess it's not fault of this patch, but some more
> deep problem instead.
> The sequence is my usual copy of an oracle database from another
> place and start it.  When oracle starts doing it's direct-I/O
> against its redologs, we had problem which is now solved.  But
> now I do the following: I shutdown the database, rename the current
> redologs out of the way and copy them back into place as new files.
> And start the database again.
> This time, oracle complains that the redologs contains garbage.
> I can reboot the machine now, and compare old (renamed) redologs
> with copies - they're indeed different.
> My guess is that copy is done from the pagecache - from the old
> contents of the files, somehow ignoring the (direct) writes
> performed by initial database open.  But that copy is somehow
> damaged now too, since even file identification is now different.
> Is this new issue something that dioread_nolock supposed to create?
> I mean, it isn't entirely clear what it supposed to do, it looks
> somewhat hackish, but without it performance is quite bad.
So could I generalize your sequence like below:
1. copy a large file to a new ext4 volume
2. do some direct i/o read/write to this file(bs=512)
3. rename it.
4. cp this back to the original file
5. do direct i/o read/write(bs=512) now and the file is actually corrupted.

You used to meet with problem in step 2, and my patch resolved it. Now
you met with problems in step 5. Right?

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