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

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Thu, Apr 10, 2014 at 07:26:52PM -0400, Dave Jones wrote:
> 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.

Whew!!!  ;-)

							Thanx, Paul