From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758470AbZCMNKI (ORCPT ); Fri, 13 Mar 2009 09:10:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756633AbZCMNIV (ORCPT ); Fri, 13 Mar 2009 09:08:21 -0400 Received: from hera.kernel.org ([140.211.167.34]:36753 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759216AbZCMNIR (ORCPT ); Fri, 13 Mar 2009 09:08:17 -0400 Date: Fri, 13 Mar 2009 13:06:43 GMT From: Peter Zijlstra To: linux-tip-commits@vger.kernel.org Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@redhat.com, a.p.zijlstra@chello.nl, tglx@linutronix.de, mingo@elte.hu Reply-To: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, tglx@linutronix.de, mingo@elte.hu In-Reply-To: <20090313112301.384074618@chello.nl> References: <20090313112301.384074618@chello.nl> Subject: [tip:perfcounters/core] perf_counter: add comment to barrier Message-ID: Git-Commit-ID: ffd25c2b454557dd5a09b23d2446d1800d497bde X-Mailer: tip-git-log-daemon MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.0 (hera.kernel.org [127.0.0.1]); Fri, 13 Mar 2009 13:06:45 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: ffd25c2b454557dd5a09b23d2446d1800d497bde Gitweb: http://git.kernel.org/tip/ffd25c2b454557dd5a09b23d2446d1800d497bde Author: Peter Zijlstra AuthorDate: Fri, 13 Mar 2009 12:21:30 +0100 Commit: Ingo Molnar CommitDate: Fri, 13 Mar 2009 14:02:43 +0100 perf_counter: add comment to barrier We need to ensure the enabled=0 write happens before we start disabling the actual counters, so that a pcm_amd_enable() will not enable one underneath us. I think the race is impossible anyway, we always balance the ops within any one context and perform enable() with IRQs disabled. Signed-off-by: Peter Zijlstra LKML-Reference: <20090313112301.384074618@chello.nl> Signed-off-by: Ingo Molnar --- arch/x86/kernel/cpu/perf_counter.c | 4 ++++ 1 files changed, 4 insertions(+), 0 deletions(-) diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c index 1cedc34..a2e3b76 100644 --- a/arch/x86/kernel/cpu/perf_counter.c +++ b/arch/x86/kernel/cpu/perf_counter.c @@ -247,6 +247,10 @@ static u64 pmc_amd_save_disable_all(void) enabled = cpuc->enabled; cpuc->enabled = 0; + /* + * ensure we write the disable before we start disabling the + * counters proper, so that pcm_amd_enable() does the right thing. + */ barrier(); for (idx = 0; idx < nr_counters_generic; idx++) {