linux-kernel - Re: [RESEND PATCH 1/2] perf, cpu hotplug: Run CPU

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Message-ID: <20121016183431.GF2385@linux.vnet.ibm.com>
Date:	Tue, 16 Oct 2012 11:34:31 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	peterz@...radead.org, acme@...stprotocols.net, mingo@...nel.org,
	tglx@...utronix.de, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH 1/2] perf, cpu hotplug: Run CPU_STARTING notifiers
 with irqs disabled

On Tue, Oct 16, 2012 at 10:07:15PM +0530, Srivatsa S. Bhat wrote:
> On 10/16/2012 10:01 PM, Paul E. McKenney wrote:
> > On Tue, Oct 16, 2012 at 01:28:10PM +0530, Srivatsa S. Bhat wrote:
> >> The CPU_STARTING notifiers are supposed to be run with irqs disabled. But the
> >> perf_cpu_notifier() macro invokes them without doing that. Fix it.
> > 
> > Color me confused...
> 
> Hehe, I believe the context provided by diff tricked you ;-)
> The function I am referring to is perf_cpu_notifier(), not
> perf_event_task_tick() :-)

It did indeed fool me!  And indeed, checking the code did indeed show
that the name of interest if perf_cpu_notifier().

When using the correct name, I do indeed find places where it is
called with interrupts enabled.  So...

Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

> Regards,
> Srivatsa S. Bhat
> 
> >  Isn't perf_event_task_tick() invoked only
> > from scheduler_tick(), which always has interrupts disabled?
> > 
> > Or are you needing to invoke it from somewhere else?
> > 
> > 							Thanx, Paul
> > 
> >> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
> >> ---
> >>
> >>  include/linux/perf_event.h |    3 +++
> >>  1 file changed, 3 insertions(+)
> >>
> >> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> >> index 2e90235..0647805 100644
> >> --- a/include/linux/perf_event.h
> >> +++ b/include/linux/perf_event.h
> >> @@ -803,10 +803,13 @@ static inline void perf_event_task_tick(void)				{ }
> >>  do {									\
> >>  	static struct notifier_block fn##_nb __cpuinitdata =		\
> >>  		{ .notifier_call = fn, .priority = CPU_PRI_PERF };	\
> >> +	unsigned long flags;						\
> >>  	fn(&fn##_nb, (unsigned long)CPU_UP_PREPARE,			\
> >>  		(void *)(unsigned long)smp_processor_id());		\
> >> +	local_irq_save(flags);						\
> >>  	fn(&fn##_nb, (unsigned long)CPU_STARTING,			\
> >>  		(void *)(unsigned long)smp_processor_id());		\
> >> +	local_irq_restore(flags);					\
> >>  	fn(&fn##_nb, (unsigned long)CPU_ONLINE,				\
> >>  		(void *)(unsigned long)smp_processor_id());		\
> >>  	register_cpu_notifier(&fn##_nb);				\
> >>
> 

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