linux-kernel - Re: [PATCH v2] arm, hw-breakpoint: Remove superfluous SMP function call

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Message-ID: <20160407113448.GF5657@arm.com>
Date:	Thu, 7 Apr 2016 12:34:48 +0100
From:	Will Deacon <will.deacon@....com>
To:	Anna-Maria Gleixner <anna-maria@...utronix.de>
Cc:	linux-kernel@...r.kernel.org, rt@...utronix.de,
	Mark Rutland <mark.rutland@....com>,
	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] arm, hw-breakpoint: Remove superfluous SMP function
 call

On Wed, Apr 06, 2016 at 10:40:30AM +0200, Anna-Maria Gleixner wrote:
> Since commit 1cf4f629d9d2 ("cpu/hotplug: Move online calls to
> hotplugged cpu") it is ensured that callbacks of CPU_ONLINE and
> CPU_DOWN_PREPARE are processed on the hotplugged CPU. Due to this SMP
> function calls are no longer required.
> 
> Replace smp_call_function_single() with a direct call of
> reset_ctrl_regs(). To keep the calling convention, interrupts are
> explicitly disabled around the call.
> 
> Cc: Will Deacon <will.deacon@....com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Russell King <linux@....linux.org.uk>
> Cc: linux-arm-kernel@...ts.infradead.org
> Signed-off-by: Anna-Maria Gleixner <anna-maria@...utronix.de>
> ---
>  arch/arm/kernel/hw_breakpoint.c |    7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> --- a/arch/arm/kernel/hw_breakpoint.c
> +++ b/arch/arm/kernel/hw_breakpoint.c
> @@ -1023,8 +1023,11 @@ static void reset_ctrl_regs(void *unused
>  static int dbg_reset_notify(struct notifier_block *self,
>  				      unsigned long action, void *cpu)
>  {
> -	if ((action & ~CPU_TASKS_FROZEN) == CPU_ONLINE)
> -		smp_call_function_single((int)cpu, reset_ctrl_regs, NULL, 1);
> +	if ((action & ~CPU_TASKS_FROZEN) == CPU_ONLINE) {
> +		local_irq_disable();
> +		reset_ctrl_regs(NULL);
> +		local_irq_enable();
> +	}
>  
>  	return NOTIFY_OK;
>  }

Acked-by: Will Deacon <will.deacon@....com>

Will