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Date: Mon, 30 Apr 2012 09:05:25 -0400 From: Don Zickus <dzickus@...hat.com> To: "Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com> Cc: Sameer Nanda <snanda@...omium.org>, mingo@...hat.com, peterz@...radead.org, len.brown@...el.com, pavel@....cz, rjw@...k.pl, akpm@...ux-foundation.org, msb@...omium.org, linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, olofj@...omium.org Subject: Re: [PATCH] watchdog: fix for lockup detector breakage on resume On Mon, Apr 30, 2012 at 11:42:13AM +0530, Srivatsa S. Bhat wrote: > > +void lockup_detector_bootcpu_resume(void) > > +{ > > + void *cpu = (void *)(long)smp_processor_id(); > > + > > + /* > > + * On the suspend/resume path the boot CPU does not go though the > > + * offline->online transition. This breaks the NMI detector post > > + * resume. Force an offline->online transition for the boot CPU on > > + * resume. > > + */ > > + cpu_callback(&cpu_nfb, CPU_DEAD, cpu); > > + cpu_callback(&cpu_nfb, CPU_ONLINE, cpu); > > + > > > I have a couple of comments about this: > > 1. Strictly speaking, we should be using the _FROZEN variants here (since the > tasks are still frozen). > > Like, cpu_callback(&cpu_nfb, CPU_DEAD_FROZEN, cpu); > and cpu_callback(&cpu_nfb, CPU_ONLINE_FROZEN, cpu); > > Right now, since the same action is taken for either variant (ie., with or without > _FROZEN), it really doesn't matter. But still, good to be on the safer side no? > > 2. Why are we skipping the CPU_UP_PREPARE_FROZEN callback? > > 3. How about hibernation? We don't hit this problem there? Hi, I have similar concerns as this patch seems kinda like a hack. OTOH I don't know all the available hooks for the suspend/resume paths. I would have assumed there was a special case call for the boot cpu to shutdown or at least disable its services. Wouldn't a lot of other tasks run into similar problems as the watchdog? I don't think the watchdog does anything special that requires a special hook into the suspend path. What do other hardware timers do on the suspend path? Cheers, Don -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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