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

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Date:	Wed, 21 Jul 2010 14:11:17 +0200
From:	Jan Kara <jack@...e.cz>
To:	Stephen Rothwell <sfr@...b.auug.org.au>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Chinner <david@...morbit.com>,
	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 Wed 21-07-10 17:48:09, Stephen Rothwell wrote:
> On Wed, 21 Jul 2010 00:29:07 -0700 Andrew Morton <akpm@...ux-foundation.org> wrote:
> >
> > On Wed, 21 Jul 2010 15:20:07 +1000 Dave Chinner <david@...morbit.com> wrote:
> > 
> > > > 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 a race.  I type `make' and the warnings spew out at hundreds
> > per second - every unlink, I'd say.
> 
> Bisected to:
> 
> commit 8bfe4a06746e5f03c02afe3ceb97b5364c099f63
> Author: Al Viro <viro@...iv.linux.org.uk>
> Date:   Sun Jun 6 07:08:19 2010 -0400
> 
>     convert ext3 to ->evict_inode()
>     
>     Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
  Thanks for bisecting this. The patch series indeed seems to uncover
some discrepancies.
  Ext3 has always dirtied inode in it's ->delete_inode method (via quota
code). But previously clear_inode() just overwrote the state with I_CLEAR
and thus we never saw the BUG_ON. After Al's patches, i_state is set in
end_writeback() which happens earlier. In particular it happens before
ext3_free_inode() which dirties the inode through quota code while freeing
xattrs - they are accounted in i_blocks, so i_blocks are updated during
freeing and inode is dirtied.
  Actually, ext3_mark_inode_dirty() called during each mark_inode_dirty()
call writes the inode state to the journal so the dirty flag in the inode
state is in fact stale and overwriting it with I_CLEAR never mattered. In
this sense, the BUG_ON triggered is a false positive. But I believe this is
a separate story.
  I'm not sure how to really fix this. It seems a bit premature to me to
mark inode as I_CLEAR before the filesystem is actually done with it. So
maybe the line
  inode->i_state = I_FREEING | I_CLEAR;
should be moved to evict() fuction?

								Honza

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