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Date: Fri, 28 Sep 2012 15:05:52 -0400
From: Dave Jones <davej@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Sasha Levin <levinsasha928@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: Linux 3.6-rc4
Message-ID: <20120928190552.GA32188@redhat.com>
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On Fri, Sep 21, 2012 at 05:16:39PM -0400, Dave Jones wrote:
 > On Mon, Sep 10, 2012 at 04:36:20PM +0200, Peter Zijlstra wrote:
 >  > On Fri, 2012-09-07 at 11:39 -0700, Linus Torvalds wrote:
 >  > > Al? Please look into this. I'm not entirely sure what's going on, but
 >  > > lockdep complains about this:
 >  > > 
 >  > >  Possible interrupt unsafe locking scenario:
 >  > > 
 >  > >        CPU0                    CPU1
 >  > >        ----                    ----
 >  > >   lock(&(&p->alloc_lock)->rlock);
 >  > >                                local_irq_disable();
 >  > >                                lock(&(&new_timer->it_lock)->rlock);
 >  > >                                lock(tasklist_lock);
 >  > >   <Interrupt>
 >  > >     lock(&(&new_timer->it_lock)->rlock);
 >  > > 
 >  > >  *** DEADLOCK ***
 >  > > 
 >  > > and it looks real. IOW, if I read that right, we have the task_lock ->
 >  > > it_lock dependency through exit_itimers(), and then we have the
 >  > > tasklist_lock -> task_lock dependency everywhere else. So now it_lock
 >  > > -> tasklist_lock becomes a deadlock. 
 >  > 
 >  > Agreed, I've got the following series from Oleg queued to solve this:
 >  > 
 >  >  http://marc.info/?l=linux-kernel&m=134600821828491&w=2
 > 
 > What's happening with this series ? I'm still seeing these traces in rc6.

and still in rc7.

Peter ?

	Dave