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Re: BUG: soft lockup - is this XFS problem?

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: BUG: soft lockup - is this XFS problem?
From: Nick Piggin <npiggin@xxxxxxx>
Date: Mon, 5 Jan 2009 05:19:59 +0100
Cc: Peter Klotz <peter.klotz@xxxxxx>, Roman Kononov <kernel@xxxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <20090105014821.GA367@xxxxxxxxxxxxx>
References: <gifgp1$8ic$1@xxxxxxxxxxxxx> <20081223171259.GA11945@xxxxxxxxxxxxx> <20081230042333.GC27679@xxxxxxxxxxxxx> <20090103214443.GA6612@xxxxxxxxxxxxx> <20090105014821.GA367@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.9i
On Mon, Jan 05, 2009 at 02:48:21AM +0100, Nick Piggin wrote:
> On Sat, Jan 03, 2009 at 04:44:43PM -0500, Christoph Hellwig wrote:
> > On Tue, Dec 30, 2008 at 05:23:33AM +0100, Nick Piggin wrote:
> > > On Tue, Dec 23, 2008 at 12:12:59PM -0500, Christoph Hellwig wrote:
> > > > 
> > > > Nick, I've seen various reports like this by Roman.  It seems to be
> > > > caused by an interaction of the lockless pagecache with the xfs
> > > > I/O code.  Any idea what might be wrong here:
> > > 
> > > Hmm, it could get into a loop here if there is a page in the pagecache
> > > with a zero refcount, which might be a problem with XFS... other looping
> > > conditions might indicate a problem iwth lockless pagecache or radix
> > > tree. It would be very helpful to know what condition it is looping on...
> > 
> > See http://oss.sgi.com/bugzilla/show_bug.cgi?id=805
> OK.. Hmm, well here is a modification to your patch which might help further.
> I'll see if I can reproduce it here meanwhile.

I have reproduced it. It seems like it might be a livelock condition
because the system ended up recovering after I terminated the dd (and
did so before I collected any real info, oops, hopefully I can
reproduce it again).

This would fit with the problem going away when the debugging patch
was applied. Timing changes...

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