Messages in this thread | ![/](/images/icornerl.gif) | | Date | Fri, 12 Nov 2010 10:38:13 +0800 | From | DDD <> | Subject | Re: [V3 PATCH] x86: avoid calling arch_trigger_all_cpu_backtrace() at the same time on SMP |
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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();
Thanks, Dongdong
> + > +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 c90041c..bd9cb79 100644 > --- a/arch/x86/kernel/apic/nmi.c > +++ b/arch/x86/kernel/apic/nmi.c > @@ -549,9 +549,27 @@ int do_nmi_callback(struct pt_regs *regs, int cpu) > return 0; > } > > +/* "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); > > @@ -564,4 +582,9 @@ void arch_trigger_all_cpu_backtrace(void) > break; > mdelay(1); > } > + > + clear_bit(0, &backtrace_flag); > + > +out_restore_irq: > + local_irq_restore(flags); > }
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