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Re: 2.6.39-rc3, 2.6.39-rc4: XFS lockup - regression since 2.6.38

To: linux-kernel@xxxxxxxxxxxxxxx, Markus Trippelsdorf <markus@xxxxxxxxxxxxxxx>, Bruno Prémont <bonbons@xxxxxxxxxxxxxxxxx>, xfs-masters@xxxxxxxxxxx, xfs@xxxxxxxxxxx, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Alex Elder <aelder@xxxxxxx>, Dave Chinner <dchinner@xxxxxxxxxx>
Subject: Re: 2.6.39-rc3, 2.6.39-rc4: XFS lockup - regression since 2.6.38
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 5 May 2011 12:26:13 +1000
In-reply-to: <20110505002126.GA26797@dastard>
References: <20110423224403.5fd1136a@xxxxxxxxxxxx> <20110427050850.GG12436@dastard> <20110427182622.05a068a2@xxxxxxxxxxxx> <20110428194528.GA1627@xxxxxxxxxxxxxx> <20110429011929.GA13542@dastard> <20110504005736.GA2958@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> <20110505002126.GA26797@dastard>
User-agent: Mutt/1.5.20 (2009-06-14)
On Thu, May 05, 2011 at 10:21:26AM +1000, Dave Chinner wrote:
> On Wed, May 04, 2011 at 12:57:36AM +0000, Jamie Heilman wrote:
> > Dave Chinner wrote:
> > > OK, so the common elements here appears to be root filesystems
> > > with small log sizes, which means they are tail pushing all the
> > > time metadata operations are in progress. Definitely seems like a
> > > race in the AIL workqueue trigger mechanism. I'll see if I can
> > > reproduce this and cook up a patch to fix it.
> > 
> > Is there value in continuing to post sysrq-w, sysrq-l, xfs_info, and
> > other assorted feedback wrt this issue?  I've had it happen twice now
> > myself in the past week or so, though I have no reliable reproduction
> > technique.  Just wondering if more data points will help isolate the
> > cause, and if so, how to be prepared to get them.
> > 
> > For whatever its worth, my last lockup was while running
> > 2.6.39-rc5-00127-g1be6a1f with a preempt config without cgroups.
> Can you all try the patch below? I've managed to trigger a couple of
> xlog_wait() lockups in some controlled load tests. The lockups don't
> appear to occur with the following patch to he race condition in
> the AIL workqueue trigger.

They are still there, just harder to hit.

FWIW, I've also discovered that "echo 2 > /proc/sys/vm/drop_caches"
gets the system moving again because that changes the push target.

I've found two more bugs, and now my test case is now reliably
reproducably a 5-10s pause at ~1M created 1byte files and then
hanging at about 1.25M files. So there's yet another problem lurking
that I need to get to the bottom of.


Dave Chinner

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