Messages in this thread |  | | | Date | Mon, 16 Aug 2010 09:34:52 -0400 | | From | Don Zickus <> | | Subject | Re: fix BUG: using smp_processor_id() in touch_nmi_watchdog and touch_softlockup_watchdog |
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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
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