linux-ext4 - Re: Bug#615998: linux-image-2.6.32-5-xen-amd64: Repeatable "kernel BUG at fs/jbd2/commit.c:534" from Postfix on ext4

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Date:	Mon, 27 Jun 2011 16:02:51 +0200
From:	Jan Kara <jack@...e.cz>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	Jan Kara <jack@...e.cz>,
	"Moffett, Kyle D" <Kyle.D.Moffett@...ing.com>,
	Sean Ryle <seanbo@...il.com>, Ted Ts'o <tytso@....edu>,
	"615998@...s.debian.org" <615998@...s.debian.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	Sachin Sant <sachinp@...ibm.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: Bug#615998: linux-image-2.6.32-5-xen-amd64: Repeatable "kernel
 BUG at fs/jbd2/commit.c:534" from Postfix on ext4

On Mon 27-06-11 13:16:50, Lukas Czerner wrote:
> On Fri, 24 Jun 2011, Jan Kara wrote:
> 
> > On Fri 24-06-11 11:03:52, Moffett, Kyle D wrote:
> > > On Jun 24, 2011, at 09:46, Jan Kara wrote:
> > > > On Thu 23-06-11 16:19:08, Moffett, Kyle D wrote:
> > > >> Besides which, line 534 in the Debian 2.6.32 kernel I am using is this
> > > >> one:
> > > >> 
> > > >>  J_ASSERT(commit_transaction->t_nr_buffers <=
> > > >>           commit_transaction->t_outstanding_credits);
> > > > 
> > > >  Hmm, OK, so we've used more metadata buffers than we told JBD2 to
> > > > reserve. I suppose you are not using data=journal mode and the filesystem
> > > > was created as ext4 (i.e. not converted from ext3), right? Are you using
> > > > quotas?
> > > 
> > > The filesystem *is* using data=journal mode.  If I switch to data=ordered
> > > or data=writeback, the problem goes away.
> >   Ah, OK. Then bug https://bugzilla.kernel.org/show_bug.cgi?id=34642 is
> > probably ext3 incarnation of the same problem and it seems it's still
> > present even in the current kernel - that ext3 assertion triggered even
> > with 2.6.39 kernel. Frankly data=journal mode is far less tested than the
> > other two modes especially with ext4, so I'm not sure how good idea is to
> > use it in production.
 
  Hi Lukas,

> if it is so (and it probably is, since I am not testing this mode as
> well:), it would be interesting to find out whether there are many users
> of this and if there are not, which is probably the case, deprecate it now,
> so we can remove it later. If we are openly suggesting not to use this,
> then there is probably no point in having this option in the first
> place.
  For about one year I'm trying to look for people using data=journal and
I've found some. So although data=journal users are minority, there are
some. That being said I agree with you we should do something about it
- either state that we want to fully support data=journal - and then we
should really do better with testing it or deprecate it and remove it
(which would save us some complications in the code).

I would be slightly in favor of removing it (code simplicity, less options
to configure for admin, less options to test for us, some users I've come
across actually were not quite sure why they are using it - they just
thought it looks safer).

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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