From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753665Ab0KJHnh (ORCPT ); Wed, 10 Nov 2010 02:43:37 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:44534 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751406Ab0KJHnf (ORCPT ); Wed, 10 Nov 2010 02:43:35 -0500 Date: Wed, 10 Nov 2010 08:43:07 +0100 From: Ingo Molnar To: Don Zickus Cc: Peter Zijlstra , Dongdong Deng , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , 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: <20101110074307.GC29493@elte.hu> References: <1288721818-10851-1-git-send-email-dzickus@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1288721818-10851-1-git-send-email-dzickus@redhat.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 * 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 took as > unknown reason NMI interrupts. > > This patch uses a lock to avoid the problem, and stop the > arch_trigger_all_cpu_backtrace() calling to avoid dumping 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 | 14 ++++++++++++++ > arch/x86/kernel/apic/nmi.c | 14 ++++++++++++++ > 2 files changed, 28 insertions(+), 0 deletions(-) > > diff --git a/arch/x86/kernel/apic/hw_nmi.c b/arch/x86/kernel/apic/hw_nmi.c > index cefd694..3aea0a5 100644 > --- a/arch/x86/kernel/apic/hw_nmi.c > +++ b/arch/x86/kernel/apic/hw_nmi.c > @@ -29,6 +29,16 @@ u64 hw_nmi_get_sample_period(void) > void arch_trigger_all_cpu_backtrace(void) > { > int i; > + static arch_spinlock_t lock = __ARCH_SPIN_LOCK_UNLOCKED; Please dont put statics into the middle of local variables - put them into file scope in a visible way. > + unsigned long flags; > + > + local_irq_save(flags); > + if (!arch_spin_trylock(&lock)) > + /* > + * If there is already a trigger_all_cpu_backtrace() > + * in progress, don't output double cpu dump infos. > + */ > + goto out_restore_irq; > > cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask); > > @@ -41,6 +51,10 @@ void arch_trigger_all_cpu_backtrace(void) > break; > mdelay(1); > } > + > + arch_spin_unlock(&lock); > +out_restore_irq: > + local_irq_restore(flags); > } > > static int __kprobes > diff --git a/arch/x86/kernel/apic/nmi.c b/arch/x86/kernel/apic/nmi.c > index a43f71c..5fa8a13 100644 > --- a/arch/x86/kernel/apic/nmi.c > +++ b/arch/x86/kernel/apic/nmi.c > @@ -552,6 +552,16 @@ int do_nmi_callback(struct pt_regs *regs, int cpu) > void arch_trigger_all_cpu_backtrace(void) > { > int i; > + static arch_spinlock_t lock = __ARCH_SPIN_LOCK_UNLOCKED; > + unsigned long flags; > + > + local_irq_save(flags); > + if (!arch_spin_trylock(&lock)) > + /* > + * If there is already a trigger_all_cpu_backtrace() > + * in progress, don't output double cpu dump infos. > + */ > + goto out_restore_irq; > > cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask); > > @@ -564,4 +574,8 @@ void arch_trigger_all_cpu_backtrace(void) > break; > mdelay(1); > } > + > + arch_spin_unlock(&lock); > +out_restore_irq: > + local_irq_restore(flags); This spinlock is never actually used as a spinlock - it's a "in progress" flag. Why not use a flag and test_and_set_bit()? Also, the irq disabling really needed, will this code ever be called with irqs on? Thanks, Ingo