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

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Date:	Thu, 11 Nov 2010 10:23:01 +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: [PATCH] x86: avoid calling arch_trigger_all_cpu_backtrace() at
 the same time on SMP


* Dongdong Deng <dongdong.deng@...driver.com> wrote:

> +static int backtrace_flag;

> +	if (cmpxchg(&backtrace_flag, 0, 1) != 0)

Sorry to be a PITA, but i asked for test_and_set() because that's the simplest 
primitive. cmpxchg() semantics is not nearly as obvious and people regularly get it 
wrong :-/

Also, variables that cmpxchg or test_and_set operates on need to be long, not int.

	Ingo
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