linux-kernel - Re: linux-next: OOPS at boot time

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Message-ID: <20100721052007.GT32635@dastard>
Date:	Wed, 21 Jul 2010 15:20:07 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	Al Viro <viro@...iv.linux.org.uk>, linux-next@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
	Jan Kara <jack@...e.cz>
Subject: Re: linux-next: OOPS at boot time

On Tue, Jul 20, 2010 at 05:44:24PM -0700, Andrew Morton wrote:
> On Wed, 21 Jul 2010 08:45:25 +1000 Dave Chinner <david@...morbit.com> wrote:
> > On Tue, Jul 20, 2010 at 03:36:56AM -0700, Andrew Morton wrote:
> > > On Tue, 20 Jul 2010 16:41:45 +1000 Stephen Rothwell <sfr@...b.auug.org.au> wrote:
> > > > Has anyone seen this or something similar?
> > > 
> > > I get it all the time.  See the thread "Subject: Re: linux-next: Tree for
> > > July 7".
> > 
> > Yet nobody else seems to be able to reproduce it. Given that powerPC
> > is good at triggering reace conditions, maybe there is one that
> > only you are unlucky eough to trigger.
> > 
> > Rather than just commenting out the BUG_ON() and ignoring the
> > problem, can you print out the inode state (and enough information
> > to identify the filesystem the inode belongs to) before triggering
> > the BUG_ON() so we can get some idea of how this is triggering?
> 
> Already did.  ext3.  I_DIRTY_SYNC, I_DIRTY_DATASYNC and I_DIRTY_PAGES
> are set (i_state=0x67).
>
> A bit of poking around indicates that these inodes always have zero
> attached pages,

They should, because by the time that bug fires they should have had
all their pages stripped away.

> and they were dirtied within dquot_free_space().

AFAICT dquot_free_space() is called deep in the guts of
ext3_truncate() via dquot_free_block(), which is called directly
before end_writeback(). That should overwrite any state changes made
inside ext3_truncate. I wonder if iput_final() is racing with
something else here?

> This isn't necessarily a problem in the quota code (setting aside the
> question: why the heck does dquot_free_space() set I_DIRTY_PAGES??). 
> If the vfs is asked to kill off a dirty inode, it should at least clean
> the thing first.
> 
> I dunno.  That fs/inode.c patch series from Viro looks fishy.  I guess
> I get to bisect it tomorrow.

I suspect that is the only way to get to the bottom of this, short
of a reliable reproducer being discovered. I'm still trying to
reproduce it - I've even turned quota on - but I'm not having any
more luck than over the weekend, though...

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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