linux-kernel - Re: [V3 PATCH] x86: avoid calling arch_trigger_all_cpu

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Date:	Thu, 11 Nov 2010 12:17:02 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Dongdong Deng <dongdong.deng@...driver.com>
Cc:	dzickus@...hat.com, peterz@...radead.org, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [V3 PATCH] x86: avoid calling arch_trigger_all_cpu_backtrace()
 at the same time on SMP


Hm, another thing i noticed is that there's two of these:

>  #ifdef ARCH_HAS_NMI_WATCHDOG
> +/* "in progress" flag of arch_trigger_all_cpu_backtrace */
> +static unsigned long backtrace_flag;
> +
>  void arch_trigger_all_cpu_backtrace(void)
>  {
>  	int i;
> +	unsigned long flags;
> +
> +	/*
> +	 * Have to disable irq here, as the
> +	 * arch_trigger_all_cpu_backtrace() could be
> +	 * triggered by "spin_lock()" with irqs on.
> +	 */
> +	local_irq_save(flags);

> +/* "in progress" flag of arch_trigger_all_cpu_backtrace */
> +static unsigned long backtrace_flag;
> +
>  void arch_trigger_all_cpu_backtrace(void)
>  {
>  	int i;
> +	unsigned long flags;
> +
> +	/*
> +	 * Have to disable irq here, as the
> +	 * arch_trigger_all_cpu_backtrace() could be
> +	 * triggered by "spin_lock()" with irqs on.
> +	 */
> +	local_irq_save(flags);
> +
> +	if (test_and_set_bit(0, &backtrace_flag))

A fair amount of code is being duplicated in two places - which is not nice. Lets 
try to create a shared facility instead?

Thanks,

	Ingo
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