From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751360Ab1AEOIN (ORCPT ); Wed, 5 Jan 2011 09:08:13 -0500 Received: from hera.kernel.org ([140.211.167.34]:58352 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751879Ab1AEOIF (ORCPT ); Wed, 5 Jan 2011 09:08:05 -0500 Date: Wed, 5 Jan 2011 14:07:53 GMT From: tip-bot for Dongdong Deng Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@redhat.com, bruce.ashfield@windriver.com, dongdong.deng@windriver.com, tglx@linutronix.de, mingo@elte.hu, dzickus@redhat.com Reply-To: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, bruce.ashfield@windriver.com, dongdong.deng@windriver.com, tglx@linutronix.de, mingo@elte.hu, dzickus@redhat.com In-Reply-To: <1294198689-15447-2-git-send-email-dzickus@redhat.com> References: <1294198689-15447-2-git-send-email-dzickus@redhat.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:perf/core] x86: Avoid calling arch_trigger_all_cpu_backtrace() at the same time Message-ID: Git-Commit-ID: 554ec063982752e9a569ab9189eeffa3d96731b2 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.3 (hera.kernel.org [127.0.0.1]); Wed, 05 Jan 2011 14:07:54 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 554ec063982752e9a569ab9189eeffa3d96731b2 Gitweb: http://git.kernel.org/tip/554ec063982752e9a569ab9189eeffa3d96731b2 Author: Dongdong Deng AuthorDate: Tue, 4 Jan 2011 22:38:08 -0500 Committer: Ingo Molnar CommitDate: Wed, 5 Jan 2011 14:22:57 +0100 x86: Avoid calling arch_trigger_all_cpu_backtrace() at the same time The spin_lock_debug/rcu_cpu_stall detector uses trigger_all_cpu_backtrace() to dump cpu backtrace. Therefore it is possible that trigger_all_cpu_backtrace() could be called at the same time on different CPUs, which triggers and 'unknown reason NMI' warning. The following case illustrates the problem: CPU1 CPU2 ... CPU N trigger_all_cpu_backtrace() set "backtrace_mask" to cpu mask | generate NMI interrupts generate NMI interrupts ... \ | / \ | / The "backtrace_mask" will be cleaned by the first NMI interrupt at nmi_watchdog_tick(), then the following NMI interrupts generated by other cpus's arch_trigger_all_cpu_backtrace() will be taken as unknown reason NMI interrupts. This patch uses a test_and_set to avoid the problem, and stop the arch_trigger_all_cpu_backtrace() from calling to avoid dumping a double cpu backtrace info when there is already a trigger_all_cpu_backtrace() in progress. Signed-off-by: Dongdong Deng Reviewed-by: Bruce Ashfield Cc: fweisbec@gmail.com LKML-Reference: <1294198689-15447-2-git-send-email-dzickus@redhat.com> Signed-off-by: Ingo Molnar Signed-off-by: Don Zickus --- arch/x86/kernel/apic/hw_nmi.c | 13 +++++++++++++ 1 files changed, 13 insertions(+), 0 deletions(-) diff --git a/arch/x86/kernel/apic/hw_nmi.c b/arch/x86/kernel/apic/hw_nmi.c index 2b40a60..72ec29e 100644 --- a/arch/x86/kernel/apic/hw_nmi.c +++ b/arch/x86/kernel/apic/hw_nmi.c @@ -28,10 +28,20 @@ u64 hw_nmi_get_sample_period(void) /* For reliability, we're prepared to waste bits here. */ static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly; +/* "in progress" flag of arch_trigger_all_cpu_backtrace */ +static unsigned long backtrace_flag; + void arch_trigger_all_cpu_backtrace(void) { int i; + if (test_and_set_bit(0, &backtrace_flag)) + /* + * If there is already a trigger_all_cpu_backtrace() in progress + * (backtrace_flag == 1), don't output double cpu dump infos. + */ + return; + cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask); printk(KERN_INFO "sending NMI to all CPUs:\n"); @@ -43,6 +53,9 @@ void arch_trigger_all_cpu_backtrace(void) break; mdelay(1); } + + clear_bit(0, &backtrace_flag); + smp_mb__after_clear_bit(); } static int __kprobes