Messages in this thread | | | Date | Sat, 6 Jun 2009 14:54:49 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH] tick: add check for the existence of broadcast clock event device |
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Feng,
On Sat, 6 Jun 2009, Feng Tang wrote: > > If your percpu devices are always on (not affected by C3 stop) then > > you never dereference bc. So why do we need an extra check for !bc ? > > Hi tglx,
> Thanks for the explanation. But we really ran into the NULL pointer > case, in our platform, there are 2 X86 CPUs which have lapic, also > it has 2 external timers which are pretty similar with HPET timers, > those 2 external timers will be used as per-cpu timers (higher > rating than lapic timer). In system's power cycle of suspend and > resume, disable_nontboot_cpus will be called before goto suspend > state,and enable_nonboot_cpus will be called for the resume process, > so lapic timer of cpu1 will be first registered as per-cpu timer, > and our external timer will be registered later after get a > CPU_ONLINE notifier (similar with HPET), right in this time slot > that lapic is the per-cpu timer, when system get the > CLOCK_EVT_BROADCAST_ENTER/EXIT msg, tick_do_broadcast_on_off() is > called and hit the NULL pointer case.
Ok, I can understand now why we need it. I'll apply your patch and add some more info into the commit msg so we do not look at it in a year and scratch our heads. :)
> Our external timer driver is very similar with HPET dirver, why HPET > doesn't see such an issue? becuase HPET has enough number of timers, > and it use "hpet0" as the bc device, while our platform doesn't have > a extra one to act as bc.
Correct.
Thanks,
tglx
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