Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759087Ab0KRP5d (ORCPT ); Thu, 18 Nov 2010 10:57:33 -0500 Received: from mail-fx0-f46.google.com ([209.85.161.46]:40465 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753255Ab0KRP5c (ORCPT ); Thu, 18 Nov 2010 10:57:32 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=j85orrSQMLqEEi8AXehO/OHz9URVB2HtTVujBVHWsoZ48SfgTvOgGlR/fVywIdtKRZ Q4znT3vxFwzugiKSIfnDYZ4NwMTpipWjzndtLMSeYTHH4rAGyl+b81jmb1t81TJS7cmE pgIadb91yio9RnS2FzfH80jsPV2oeVqI43zz8= Date: Thu, 18 Nov 2010 16:57:26 +0100 From: Frederic Weisbecker To: Don Zickus Cc: Ingo Molnar , LKML , Dongdong Deng , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org Subject: Re: [PATCH 3/3] x86: Avoid calling arch_trigger_all_cpu_backtrace() at the same time Message-ID: <20101118155722.GC5374@nowhere> References: <1289573455-3410-1-git-send-email-dzickus@redhat.com> <1289573455-3410-3-git-send-email-dzickus@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1289573455-3410-3-git-send-email-dzickus@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3721 Lines: 107 On Fri, Nov 12, 2010 at 09:50:55AM -0500, Don Zickus wrote: > From: Dongdong Deng > > 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: Thomas Gleixner > CC: Ingo Molnar > CC: "H. Peter Anvin" > CC: x86@kernel.org > CC: linux-kernel@vger.kernel.org > Signed-off-by: Don Zickus > --- > arch/x86/kernel/apic/hw_nmi.c | 24 ++++++++++++++++++++++++ > 1 files changed, 24 insertions(+), 0 deletions(-) > > diff --git a/arch/x86/kernel/apic/hw_nmi.c b/arch/x86/kernel/apic/hw_nmi.c > index f349647..d892896 100644 > --- a/arch/x86/kernel/apic/hw_nmi.c > +++ b/arch/x86/kernel/apic/hw_nmi.c > @@ -27,9 +27,27 @@ 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; > + 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); I'm not sure I understand why you disable irqs here. It looks safe with the test_and_set_bit already. > + > + 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. > + */ > + goto out_restore_irq; > > cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask); > > @@ -42,6 +60,12 @@ void arch_trigger_all_cpu_backtrace(void) > break; > mdelay(1); > } > + > + clear_bit(0, &backtrace_flag); > + smp_mb__after_clear_bit(); > + > +out_restore_irq: > + local_irq_restore(flags); > } > > static int __kprobes > -- > 1.7.2.3 > > -- > 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/ -- 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/