Messages in this thread | | | Date | Mon, 18 Oct 2010 14:03:12 -0400 | From | Don Zickus <> | Subject | Re: [PATCH] x86: avoid calling arch_trigger_all_cpu_backtrace() at the same time on SMP |
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On Mon, Oct 18, 2010 at 07:00:15PM +0800, DDD wrote: > CC to Ingo's mingo@elte.hu and add some code explains for this patch. > > Dongdong > > > 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:
The patch seems reasonable. I can queue it up. Ingo wrote the original code and knows which spin locks to use better than me, perhaps he can find a moment to comment.
Cheers, Don
> > > > 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 > >--- > > 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; > > Why an arch spin lock vs just using a raw spin lock? > for example. static DEFINE_RAW_SPINLOCK(lock); > > The spin_lock_debug detector was used in raw_spinlock too. > > arch_trigger_all_cpu_backtrace() --> > raw_spin_lock(lock) --> > _raw_spin_lock(lock) --> > __raw_spin_lock(lock) --> > do_raw_spin_lock(lock) --> > __spin_lock_debug(lock) --> > trigger_all_cpu_backtrace() > > Therefor, we have to use arch spin lock here. > > > > >+ unsigned long flags; > >+ > >+ local_irq_save(flags); > > Why have to save the irq's here? > > When the arch_trigger_all_cpu_backtrace() was triggered by > "spin_lock()"'s spin_lock_debug detector, it is possible that > the irq is enabled, thus we have to save and disable it here. > > > > >+ 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); > > } > > > > > > -- > 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/
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