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SubjectRe: hunt for 2.6.37 dm-crypt+ext4 corruption? (was: Re: dm-crypt barrier support is effective)
On Tue, Dec 7, 2010 at 2:02 PM, Chris Mason <chris.mason@oracle.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@oracle.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:
>
> 1) Is postgres using O_DIRECT?  If yes, please turn it off

According to strace, O_DIRECT didn't show up once during the test.

> 2) Is postgres allocating sparse files?  If yes, please have it fully
> allocate the file instead.

That's a tough one. I don't think postgresql does that, but I'm not an
expert here.

> 3) Is postgres using preallocation (fallocate)?  If yes, please have it
> fully allocate the file instead

As far as strace is concerned, postgreql is not using fallocate in
this version.

--
Jon
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