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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Message-ID: <20110901151744.GA2070@quack.suse.cz>
Date:	Thu, 1 Sep 2011 17:17:44 +0200
From:	Jan Kara <jack@...e.cz>
To:	"Moffett, Kyle D" <Kyle.D.Moffett@...ing.com>
Cc:	Jan Kara <jack@...e.cz>, 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 Tue 30-08-11 19:26:22, Moffett, Kyle D wrote:
> On Aug 30, 2011, at 18:12, Jan Kara wrote:
> >> I can still trigger it on my VM snapshot very easily, so if you have anything
> >> you think I should test I would be very happy to give it a shot.
> > 
> >  OK, so in the meantime I found a bug in data=journal code which could be
> > related to your problem. It is fixed by commit
> > 2d859db3e4a82a365572592d57624a5f996ed0ec which is in 3.1-rc1. Have you
> > tried that or newer kernel as well?
> > 
> > If the problem still is not fixed, I can provide some debugging patch to
> > you. We spoke with Josef Bacik how errors like yours could happen so I have
> > some places to watch...
> 
> I have not tried anything more recent; I'm actually a bit reluctant to move
> away from the Debian squeeze official kernels since I do need the security
> updates.
> 
> I took a quick look and I can't find that function in 2.6.32, so I assume it
> would be a rather nontrivial back-port.  It looks like the relevant code
> used to be in ext4_clear_inode somewhere?
  It's not that hard - untested patch attached.

> Out of curiosity, what would happen in data=journal mode if you unlinked a
> file which still had buffers pending?  That case does not seem to be handled
> by that commit you mentioned, was it already handled elsewhere?
  Once the file is deleted, it's OK to discard its data after a
transaction doing delete commits. The current code in JBD2 handles this
case fine - the problem was that for not-deleted files we cannot discard
dirty data after a transaction commits ;)

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

View attachment "ext4-2.6.32-data-journal-corruption.diff" of type "text/x-patch" (3022 bytes)