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Date:	Tue, 7 Dec 2010 21:29:26 -0600
From:	Jon Nelson <jnelson@...poni.net>
To:	Chris Mason <chris.mason@...cle.com>
Cc:	Mike Snitzer <snitzer@...hat.com>, Matt <jackdachef@...il.com>,
	Milan Broz <mbroz@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	linux-btrfs <linux-btrfs@...r.kernel.org>,
	dm-devel <dm-devel@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	htd <htd@...cy-poultry.org>, htejun <htejun@...il.com>,
	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: hunt for 2.6.37 dm-crypt+ext4 corruption? (was: Re: dm-crypt
 barrier support is effective)

On Tue, Dec 7, 2010 at 3:02 PM, Chris Mason <chris.mason@...cle.com> wrote:
> Excerpts from Jon Nelson's message of 2010-12-07 15:48:58 -0500:
>> On Tue, Dec 7, 2010 at 2:41 PM, Chris Mason <chris.mason@...cle.com> wrote:
>> > Excerpts from Jon Nelson's message of 2010-12-07 15:25:47 -0500:
>> >> On Tue, Dec 7, 2010 at 2:02 PM, Chris Mason <chris.mason@...cle.com> wrote:
>> >> > Excerpts from Jon Nelson's message of 2010-12-07 14:34:40 -0500:
>> >> >> On Tue, Dec 7, 2010 at 12:52 PM, Chris Mason <chris.mason@...cle.com> wrote:
>> >> >> >> postgresql errors. Typically, header corruption but from the limited
>> >> >> >> visibility I've had into this via strace, what I see is zeroed pages
>> >> >> >> where there shouldn't be.
>> >> >> >
>> >> >> > This sounds a lot like a bug higher up than dm-crypt.  Zeros tend to
>> >> >> > come from some piece of code explicitly filling a page with zeros, and
>> >> >> > that often happens in the corner cases for O_DIRECT and a few other
>> >> >> > places in the filesystem.
>> >> >> >
>> >> >> > Have you tried triggering this with a regular block device?
>> >> >>
>> >> >> I just tried the whole set of tests, but with /dev/sdb directly (as
>> >> >> ext4) without any crypt-y bits.
>> >> >> It takes more iterations but out of 6 tests I had one failure: same
>> >> >> type of thing, 'invalid page header in block ....'.
>> >> >>
>> >> >> I can't guarantee that it is a full-page of zeroes, just what I saw
>> >> >> from the (limited) stracing I did.
>> >> >
>> >> > Fantastic. Now for our usual suspects:

Maybe not so fantastic. I kept testing and had no more failures. At
all. After 40+ iterations I gave up.
I went back to trying ext4 on a LUKS volume. The 'hit' ratio went to
something like 1 in 3, or better.

I will continue to do testing with and without LUKS. I did /not/
reboot between tests, but I do start with a fresh postgres database.

-- 
Jon
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