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

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Date:	Tue, 16 Oct 2012 09:31:41 -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 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...  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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