linux-kernel - Re: nfsd oops on Linus' current tree.

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Message-ID: <4FA345DA4F4AE44899BD2B03EEEC2FA9119886EE@SACEXCMBX04-PRD.hq.netapp.com>
Date:	Thu, 3 Jan 2013 22:12:32 +0000
From:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
To:	Tejun Heo <tj@...nel.org>
CC:	"J. Bruce Fields" <bfields@...ldses.org>,
	"Adamson, Dros" <Weston.Adamson@...app.com>,
	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>
Subject: Re: nfsd oops on Linus' current tree.

On Thu, 2013-01-03 at 17:08 -0500, Tejun Heo wrote:
> Hello,
> 
> On Thu, Jan 03, 2013 at 03:11:20PM -0500, J. Bruce Fields wrote:
> > Both rpciod and nfsiod already set WQ_MEM_RECLAIM.
> > 
> > But, right, looking at kernel/workqueue.c, it seems that the dedicated
> > "rescuer" threads are invoked only in the case when work is stalled
> > because a new worker thread isn't allocated quickly enough.
> 
> Because that's the *only* case where progress can't be guaranteed
> otherwise.
> 
> > So, what to do that's simplest enough that it would work for
> > post-rc2/stable?  I was happy having just a simple dedicated
> > thread--these are only started when nfsd is, so there's no real thread
> > proliferation problem.
> 
> The analysis is likely completely wrong, so please don't go off doing
> something unnecessary.  Please take look at what's causing the
> deadlocks again.

The analysis is a no-brainer:
We see a deadlock due to one work item waiting for completion of another
work item that is queued on the same CPU. There is no other dependency
between the two work items.

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@...app.com
www.netapp.com
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