Messages in this thread | | | Date | Fri, 19 Nov 2010 11:00:25 +0800 | From | DDD <> | Subject | Re: [PATCH 3/3] x86: Avoid calling arch_trigger_all_cpu_backtrace() at the same time |
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Frederic Weisbecker wrote: > 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.
Hi Frederic,
Yep, after we use test_and_set_bit to replace spin_lock, the disable irqs ops obvious could be removed here.
I will redo this patch, and send it to Don.
Thanks, Dongdong
> > > >> + >> + 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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