Messages in this thread | | | Date | Thu, 11 Nov 2010 22:39:54 -0500 | From | Don Zickus <> | Subject | Re: [V3 PATCH] x86: avoid calling arch_trigger_all_cpu_backtrace() at the same time on SMP |
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On Fri, Nov 12, 2010 at 10:38:13AM +0800, DDD wrote: > Dongdong Deng wrote: > >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 <dongdong.deng@windriver.com> > >Reviewed-by: Bruce Ashfield <bruce.ashfield@windriver.com> > >CC: Thomas Gleixner <tglx@linutronix.de> > >CC: Ingo Molnar <mingo@redhat.com> > >CC: "H. Peter Anvin" <hpa@zytor.com> > >CC: x86@kernel.org > >CC: linux-kernel@vger.kernel.org > >Signed-off-by: Don Zickus <dzickus@redhat.com> > >--- > > arch/x86/kernel/apic/hw_nmi.c | 23 +++++++++++++++++++++++ > > arch/x86/kernel/apic/nmi.c | 23 +++++++++++++++++++++++ > > 2 files changed, 46 insertions(+), 0 deletions(-) > > > >diff --git a/arch/x86/kernel/apic/hw_nmi.c b/arch/x86/kernel/apic/hw_nmi.c > >index cefd694..bfdab3b 100644 > >--- a/arch/x86/kernel/apic/hw_nmi.c > >+++ b/arch/x86/kernel/apic/hw_nmi.c > >@@ -26,9 +26,27 @@ u64 hw_nmi_get_sample_period(void) > > } > > #ifdef ARCH_HAS_NMI_WATCHDOG > >+/* "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); > >+ > >+ 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); > >@@ -41,6 +59,11 @@ void arch_trigger_all_cpu_backtrace(void) > > break; > > mdelay(1); > > } > >+ > >+ clear_bit(0, &backtrace_flag); > > Hi Don, > > The clear_bit() on x86 (arch/x86/include/asm/bitops.h) does not > contain a memory barrier, Could you add a memory barrier ops here > when you pick up this patch? > > + clear_bit(0, &backtrace_flag); > + smp_mb__after_clear_bit(); > >
Ok. Thanks.
Cheers, Don
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