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Date:	Mon, 9 Nov 2009 15:02:33 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Ingo Molnar <mingo@...e.hu>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	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 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.

Thanks,

	tglx
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