linux-ext4 - Re: [PATCH] jbd jbd2: fix dio write returning EIO when try_to_release

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Date:	Mon, 04 Aug 2008 23:35:53 -0400
From:	Chris Mason <chris.mason@...cle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>, cmm@...ibm.com,
	jack@...e.cz, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] jbd jbd2: fix dio write returning EIO when
	try_to_release_page fails

On Mon, 2008-08-04 at 14:50 -0700, Andrew Morton wrote:
> On Mon, 04 Aug 2008 20:10:33 +0900
> Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp> wrote:
> 
> > Hi
> > 
> > Dio write returns EIO when try_to_release_page fails because bh is
> > still referenced.

> > 
> > diff -Nrup linux-2.6.27-rc1.org/fs/jbd/transaction.c linux-2.6.27-rc1/fs/jbd/transaction.c
> > --- linux-2.6.27-rc1.org/fs/jbd/transaction.c	2008-07-29 19:28:47.000000000 +0900
> > +++ linux-2.6.27-rc1/fs/jbd/transaction.c	2008-07-29 20:40:12.000000000 +0900
> > @@ -1764,6 +1764,12 @@ int journal_try_to_free_buffers(journal_
> >  	*/
> >  	if (ret == 0 && (gfp_mask & __GFP_WAIT) && (gfp_mask & __GFP_FS)) {
> >  		journal_wait_for_transaction_sync_data(journal);
> > +
> > +		bh = head;
> > +		do {
> > +			while (atomic_read(&bh->b_count))
> > +				schedule();
> > +		} while ((bh = bh->b_this_page) != head);
> >  		ret = try_to_free_buffers(page);
> >  	}
> 
> The loop is problematic.  If the scheduler decides to keep running this
> task then we have a busy loop.  If this task has realtime policy then
> it might even lock up the kernel.
> 

ocfs2 calls journal_try_to_free_buffers too, looping on b_count might
not be the best idea there either.

This code gets called from releasepage, which is used other places than
the O_DIRECT invalidation paths, I'd be worried about performance
problems here.

-chris


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