[dm-devel] hunt for 2.6.37 dm-crypt+ext4 corruption? (was: Re: dm-crypt barrier support is effective)

[Jon Nelson]

On Tue, Dec 7, 2010 at 12:52 PM, Chris Mason <chris.mason at oracle.com> wrote:
> Excerpts from Jon Nelson's message of 2010-12-07 13:45:14 -0500:
>> On Tue, Dec 7, 2010 at 12:22 PM, Mike Snitzer <snitzer at redhat.com> wrote:
>> > On Tue, Dec 07 2010 at  1:10pm -0500,
>> > Jon Nelson <jnelson at jamponi.net> wrote:
>> >
>> >> I finally found some time to test this out. With 2.6.37-rc4 (openSUSE
>> >> KOTD kernel) I easily encounter the issue.
>> >>
>> >> Using a virtual machine, I created a stock, minimal openSUSE 11.3 x86_64
>> >> install, installed all updates, installed postgresql and the 'KOTD'
>> >> (Kernel of the Day)
>> >> kernel, and ran the following tests (as postgres user because I'm
>> >> lazy).
>> >>
>> >> 1. create a database (from bash):
>> >>
>> >> createdb test
>> >>
>> >> 2. place the following contents in a file (I used 't.sql'):
>> >>
>> >> begin;
>> >> create temporary table foo as select x as a, ARRAY[x] as b FROM
>> >> generate_series(1, 10000000 ) AS x;
>> >> create index foo_a_idx on foo (a);
>> >> create index foo_b_idx on foo USING GIN (b);
>> >> rollback;
>> >>
>> >> 3. execute that sql:
>> >>
>> >> psql -f t.sql --echo-all test
>> >>
>> >>
>> >> With 2.6.34.7 I can re-run [3] all day long, as many times as I want,
>> >> without issue.
>> >>
>> >> With 2.6.37-rc4-13 (the currently-installed KOTD kernel) if tails
>> >> pretty frequently.
>> >
>> > How does it fail?  postgres errors?  kernel errors?
>>
>> 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.



-- 
Jon