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Date: Tue, 5 Apr 2016 13:23:36 +0200 From: Heiko Carstens <heiko.carstens@...ibm.com> To: Sebastian Andrzej Siewior <sebastian.siewior@...utronix.de> Cc: Anna-Maria Gleixner <anna-maria@...utronix.de>, Martin Schwidefsky <schwidefsky@...ibm.com>, linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org, rt@...utronix.de Subject: Re: [PREEMPT-RT] [PATCH] s390/cpum_sf: Remove superfluous SMP function call On Tue, Apr 05, 2016 at 01:13:06PM +0200, Sebastian Andrzej Siewior wrote: > On 04/05/2016 12:49 PM, Heiko Carstens wrote: > >> --- a/arch/s390/kernel/perf_cpum_sf.c > >> +++ b/arch/s390/kernel/perf_cpum_sf.c > >> @@ -1510,7 +1510,6 @@ static void cpumf_measurement_alert(stru > >> static int cpumf_pmu_notifier(struct notifier_block *self, > >> unsigned long action, void *hcpu) > >> { > >> - unsigned int cpu = (long) hcpu; > >> int flags; > >> > >> /* Ignore the notification if no events are scheduled on the PMU. > >> @@ -1523,11 +1522,15 @@ static int cpumf_pmu_notifier(struct not > >> case CPU_ONLINE: > >> case CPU_DOWN_FAILED: > >> flags = PMC_INIT; > >> - smp_call_function_single(cpu, setup_pmc_cpu, &flags, 1); > >> + local_irq_disable(); > >> + setup_pmc_cpu(&flags); > >> + local_irq_enable(); > >> break; > > > > ...but at least the CPU_DOWN_FAILED callback will not necessarily be called > > on the cpu that couldn't be brought offline. > > I don't follow. I was trying to say that if bringing a cpu down fails, then the cpu hotplug notifier with CPU_DOWN_FAILED might be called on a cpu that is _not_ the same cpu that was supposed to be brought offline. Subsequently, in this case, the setup_pmc_cpu() call will be executed on the wrong cpu.
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