linux-kernel - Re: Help needed: Resume problems in 2.6.32-rc, perhaps related to preempt

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Message-Id: <200911091526.02147.rjw@sisk.pl>
Date:	Mon, 9 Nov 2009 15:26:02 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	Greg KH <gregkh@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: Help needed: Resume problems in 2.6.32-rc, perhaps related to preempt_count leakage in keventd

On Monday 09 November 2009, Thomas Gleixner wrote:
> On Mon, 9 Nov 2009, Ingo Molnar wrote:
> > 
> > * Rafael J. Wysocki <rjw@...k.pl> wrote:
> > 
> > > On Monday 09 November 2009, Ingo Molnar wrote:
> > > > 
> > > > * Rafael J. Wysocki <rjw@...k.pl> wrote:
> > > > 
> > > > > [ 2016.865041] BUG: using smp_processor_id() in preemptible [00000000] code: events/1/29920                                                                                         
> > > > > [ 2016.865344] caller is vmstat_update+0x13/0x48                                          
> > > > > [ 2016.865522] Pid: 29920, comm: events/1 Not tainted 2.6.31-tst #158                     
> > > > > [ 2016.865700] Call Trace:                                                                
> > > > > [ 2016.865877]  [<ffffffff811608e8>] debug_smp_processor_id+0xc4/0xd4                     
> > > > > [ 2016.866052]  [<ffffffff810a9ae1>] vmstat_update+0x13/0x48                              
> > > > > [ 2016.866232]  [<ffffffff81051ee6>] worker_thread+0x18b/0x22a                            
> > > > > [ 2016.866409]  [<ffffffff810a9ace>] ? vmstat_update+0x0/0x48                             
> > > > > [ 2016.866578]  [<ffffffff810556a5>] ? autoremove_wake_function+0x0/0x38                  
> > > > > [ 2016.866749]  [<ffffffff81288803>] ? _spin_unlock_irqrestore+0x35/0x37                  
> > > > > [ 2016.866935]  [<ffffffff81051d5b>] ? worker_thread+0x0/0x22a                            
> > > > > [ 2016.867113]  [<ffffffff8105547d>] kthread+0x69/0x71                                    
> > > > > [ 2016.867278]  [<ffffffff8100c1aa>] child_rip+0xa/0x20                                   
> > > > > [ 2016.867450]  [<ffffffff81055414>] ? kthread+0x0/0x71                                   
> > > > > [ 2016.867618]  [<ffffffff8100c1a0>] ? child_rip+0x0/0x20                                 
> > > > 
> > > > a bug producing similar looking messages was fixed by:
> > > > 
> > > >   fd21073: sched: Fix affinity logic in select_task_rq_fair()
> > > > 
> > > > but that bug was introduced by:
> > > > 
> > > >   a1f84a3: sched: Check for an idle shared cache in select_task_rq_fair()
> > > 
> > > I guess these are tip commits?
> > 
> > yep, tip:sched/core ones.
> > 
> > > > Which is for v2.6.33, not v2.6.32.
> > > 
> > > The one I saw was in the Linus' tree, quite obviously.
> > 
> > ok, then my observation should not apply.
> 
> I think it _IS_ releated because the worker_thread is CPU affine and
> the debug_smp_processor_id() check does:
> 
>     if (cpumask_equal(&current->cpus_allowed, cpumask_of(this_cpu)))
> 
> which prevents that usage of smp_processor_id() in ksoftirqd and
> keventd in preempt enabled regions is warned on.
> 
> We saw exaclty the same back trace with fd21073 (sched: Fix affinity
> logic in select_task_rq_fair()).
> 
> Rafael, can you please add a printk to debug_smp_processor_id() so we
> can see on which CPU we are running ? I suspect we are on the wrong
> one.

Well, I can add the printk(), but I can't guarantee that I will get the call
trace once again.  So far I've seen it only once after 20-25 consecutive
suspend-resume cycles, so ...  you get the idea.

However, running on a wrong CPU would very nicely explain all of the observed
symptoms, so I guess we can try a House M.D.-alike approach and assume that the
answer is "yes, we're running on the wrong CPU".  What would we do next if that
was the case?

Rafael
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