lkml.org 
[lkml]   [2010]   [Aug]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: fix BUG: using smp_processor_id() in touch_nmi_watchdog and touch_softlockup_watchdog
On Mon, Aug 16, 2010 at 10:22:50AM +0200, Peter Zijlstra wrote:
> On Fri, 2010-08-13 at 13:21 +0300, Sergey Senozhatsky wrote:
>
> > [ 67.703556] BUG: using smp_processor_id() in preemptible [00000000] code: s2disk/5139
> > [ 67.703563] caller is touch_nmi_watchdog+0x15/0x2c
> > [ 67.703566] Pid: 5139, comm: s2disk Not tainted 2.6.36-rc0-git12-07921-g60bf26a-dirty #116
> > [ 67.703568] Call Trace:
> > [ 67.703575] [<ffffffff811f6bf1>] debug_smp_processor_id+0xc9/0xe4
> > [ 67.703578] [<ffffffff81092766>] touch_nmi_watchdog+0x15/0x2c
> > [ 67.703584] [<ffffffff81222950>] acpi_os_stall+0x34/0x40
> > [ 67.703589] [<ffffffff812398d2>] acpi_ex_system_do_stall+0x34/0x38
>
> Which could mean two things, either ACPI got funny on us, or Don's new
> watchdog stuff has a hole in it.

it could. :-)

>
>
> > ---
> >
> > diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> > index 613bc1f..8822f1e 100644
> > --- a/kernel/watchdog.c
> > +++ b/kernel/watchdog.c
> > @@ -116,13 +116,14 @@ static unsigned long get_sample_period(void)
> > static void __touch_watchdog(void)
> > {
> > int this_cpu = smp_processor_id();
> > -
> > - __get_cpu_var(watchdog_touch_ts) = get_timestamp(this_cpu);
> > + per_cpu(watchdog_touch_ts, this_cpu) = get_timestamp(this_cpu);
> > }
>
> That change seems sensible enough..

ok.

>
> > void touch_softlockup_watchdog(void)
> > {
> > - __get_cpu_var(watchdog_touch_ts) = 0;
> > + int this_cpu = get_cpu();
> > + per_cpu(watchdog_touch_ts, this_cpu) = 0;
> > + put_cpu();
> > }
> > EXPORT_SYMBOL(touch_softlockup_watchdog);
> >
> > @@ -142,7 +143,9 @@ void touch_all_softlockup_watchdogs(void)
> > #ifdef CONFIG_HARDLOCKUP_DETECTOR
> > void touch_nmi_watchdog(void)
> > {
> > - __get_cpu_var(watchdog_nmi_touch) = true;
> > + int this_cpu = get_cpu();
> > + per_cpu(watchdog_nmi_touch, this_cpu) = true;
> > + put_cpu();
> > touch_softlockup_watchdog();
> > }
> > EXPORT_SYMBOL(touch_nmi_watchdog);
>
> These other two really are about assumptions we make on the call sites,
> which at the very least are violated by ACPI.
>
> Don/Ingo, remember if we require touch_*_watchdog callers to have
> preemption disabled? Or is the proposed patch sensible?

I don't recall any requirement to have preemption disabled when using
those functions. It seems sensible to put it in the
touch_{softlockup|nmi}_watchdog code.
I assume the reason for having preemption disabled when using
smp_processor_id() is that the code could migrate to another cpu when
rescheduled?

I don't see a problem with the patch, but my low level understanding of
the __get_cpu_var vs. per_cpu isn't very strong.

Cheers,
Don

>


\
 
 \ /
  Last update: 2010-08-16 15:37    [from the cache]
©2003-2011 Jasper Spaans