Messages in this thread | | | Date | Thu, 18 Nov 2010 16:57:26 +0100 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 3/3] x86: Avoid calling arch_trigger_all_cpu_backtrace() at the same time |
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On Fri, Nov 12, 2010 at 09:50:55AM -0500, Don Zickus wrote: > From: Dongdong Deng <dongdong.deng@windriver.com> > > 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 <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 | 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/
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