Messages in this thread Patch in this message | | | From | Don Zickus <> | Subject | [PATCH 3/3] x86: Avoid calling arch_trigger_all_cpu_backtrace() at the same time | Date | Fri, 12 Nov 2010 09:50:55 -0500 |
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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); + + 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
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