linux-kernel - Re: 3.14.0+/x86: lockdep and mutexes not getting along

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Message-ID: <20140410232652.GA24658@redhat.com>
Date:	Thu, 10 Apr 2014 19:26:52 -0400
From:	Dave Jones <davej@...hat.com>
To:	Jason Low <jason.low2@...com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	"Michael L. Semon" <mlsemon35@...il.com>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	paulmck@...ux.vnet.ibm.com
Subject: Re: 3.14.0+/x86: lockdep and mutexes not getting along

On Thu, Apr 10, 2014 at 10:14:44AM -0700, Jason Low wrote:
 > On Thu, 2014-04-10 at 11:18 +0200, Peter Zijlstra wrote:
 > > On Wed, Apr 09, 2014 at 10:42:59PM -0700, Jason Low wrote:
 > > > As a starting point, would either of you like to test the following
 > > > patch to see if it fixes the issue? This patch essentially generates the
 > > > same code as in older kernels in the debug case. This applies on top of
 > > > kernels with both commits 6f008e72cd11 and 1d8fe7dc8078.
 > > 
 > > 
 > > So I managed to reproduce, and the below makes it go away. I just don't
 > > understand why though. will stare more.
 > 
 > So one thing I noticed that is different in the current code is that in
 > debug_mutex_unlock(), there is is a possibility that it does not unlock
 > the mutex (when !debug_locks). May be interesting to try out this
 > patch too:
 
I've been seeing lockups this last week or two too, that manifested by
RCU spewing stall messages, and the box being totally unresponsive.
This patch seems to cure that for me, which I'm sure will make Paul
happy to hear.

	Dave
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