From: Heiko Carstens <heiko.carstens@de.ibm.com>
To: Sebastian Andrzej Siewior <sebastian.siewior@linutronix.de>,
Anna-Maria Gleixner <anna-maria@linutronix.de>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
rt@linutronix.de
Subject: Re: [PREEMPT-RT] [PATCH] s390/cpum_sf: Remove superfluous SMP function call
Date: Tue, 5 Apr 2016 13:36:38 +0200 [thread overview]
Message-ID: <20160405113637.GC6890@osiris> (raw)
In-Reply-To: <20160405112336.GB6890@osiris>
On Tue, Apr 05, 2016 at 01:23:36PM +0200, Heiko Carstens wrote:
> 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.
.. or to illustrate this behaviour: the following patch (white space
damaged due to copy-paste) results in the following:
# chcpu -d 2
[console] failed cpu: 2 - this cpu: 1
diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index 40a6b4f9c36c..48d417abfdae 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -852,6 +852,7 @@ int __cpu_disable(void)
{
unsigned long cregs[16];
+ return -EBUSY;
/* Handle possible pending IPIs */
smp_handle_ext_call();
set_cpu_online(smp_processor_id(), false);
@@ -1065,6 +1066,10 @@ static int smp_cpu_notify(struct notifier_block *self, unsigned long action,
int err = 0;
switch (action & ~CPU_TASKS_FROZEN) {
+ case CPU_DOWN_FAILED:
+ printk("failed cpu: %d - this cpu: %d\n", cpu, get_cpu());
+ put_cpu();
+ break;
case CPU_ONLINE:
err = sysfs_create_group(&s->kobj, &cpu_online_attr_group);
break;
next prev parent reply other threads:[~2016-04-05 11:36 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-04 10:27 [PATCH] s390/cpum_sf: Remove superfluous SMP function call Anna-Maria Gleixner
2016-04-05 10:49 ` Heiko Carstens
2016-04-05 11:13 ` [PREEMPT-RT] " Sebastian Andrzej Siewior
2016-04-05 11:23 ` Heiko Carstens
2016-04-05 11:36 ` Heiko Carstens [this message]
2016-04-05 11:51 ` rcochran
2016-04-05 11:55 ` Heiko Carstens
2016-04-05 11:57 ` Sebastian Andrzej Siewior
2016-04-05 12:11 ` Heiko Carstens
2016-04-05 12:19 ` Sebastian Andrzej Siewior
2016-04-05 15:59 ` [PATCH] cpu/hotplug: fix rollback during error-out in __cpu_disable() Sebastian Andrzej Siewior
2016-04-06 19:51 ` Heiko Carstens
2016-04-07 15:14 ` Sebastian Andrzej Siewior
2016-04-08 6:19 ` Heiko Carstens
2016-04-08 12:40 ` [PATCH v2] " Sebastian Andrzej Siewior
2016-04-22 7:54 ` [tip:smp/urgent] cpu/hotplug: Fix " tip-bot for Sebastian Andrzej Siewior
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