Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753482Ab0KKJXR (ORCPT ); Thu, 11 Nov 2010 04:23:17 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:41732 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751535Ab0KKJXP (ORCPT ); Thu, 11 Nov 2010 04:23:15 -0500 Date: Thu, 11 Nov 2010 10:23:01 +0100 From: Ingo Molnar To: Dongdong Deng Cc: dzickus@redhat.com, peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86: avoid calling arch_trigger_all_cpu_backtrace() at the same time on SMP Message-ID: <20101111092301.GD18789@elte.hu> References: <1289442042-2515-1-git-send-email-dongdong.deng@windriver.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1289442042-2515-1-git-send-email-dongdong.deng@windriver.com> User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -2.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 643 Lines: 19 * Dongdong Deng 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/