Messages in this thread | | | Date | Wed, 28 Apr 2010 14:36:54 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 1/8] [watchdog] combine nmi_watchdog and softlockup |
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On Fri, Apr 23, 2010 at 12:13:29PM -0400, Don Zickus wrote: > +void watchdog_overflow_callback(struct perf_event *event, int nmi, > + struct perf_sample_data *data, > + struct pt_regs *regs) > +{ > + int this_cpu = smp_processor_id(); > + unsigned long touch_ts = per_cpu(watchdog_touch_ts, this_cpu); > + char warn = __get_cpu_var(watchdog_warn); > + > + if (touch_ts == 0) { > + __touch_watchdog(); > + return; > + } > + > + /* check for a hardlockup > + * This is done by making sure our timer interrupt > + * is incrementing. The timer interrupt should have > + * fired multiple times before we overflow'd. If it hasn't > + * then this is a good indication the cpu is stuck > + */ > + if (is_hardlockup(this_cpu)) { > + /* only print hardlockups once */ > + if (warn & HARDLOCKUP) > + return; > + > + if (hardlockup_panic) > + panic("Watchdog detected hard LOCKUP on cpu %d", this_cpu); > + else > + WARN(1, "Watchdog detected hard LOCKUP on cpu %d", this_cpu); > + > + __get_cpu_var(watchdog_warn) = warn | HARDLOCKUP; > + return; > + } > + > + __get_cpu_var(watchdog_warn) = warn & ~HARDLOCKUP; > + return; > +} [...] > +static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) > +{ > + int this_cpu = smp_processor_id(); > + unsigned long touch_ts = __get_cpu_var(watchdog_touch_ts); > + char warn = __get_cpu_var(watchdog_warn); > + struct pt_regs *regs = get_irq_regs(); > + int duration; > + > + /* kick the hardlockup detector */ > + watchdog_interrupt_count(); > + > + /* kick the softlockup detector */ > + wake_up_process(__get_cpu_var(softlockup_watchdog)); > + > + /* .. and repeat */ > + hrtimer_forward_now(hrtimer, ns_to_ktime(get_sample_period())); > + > + if (touch_ts == 0) { > + __touch_watchdog(); > + return HRTIMER_RESTART; > + } > + > + /* check for a softlockup > + * This is done by making sure a high priority task is > + * being scheduled. The task touches the watchdog to > + * indicate it is getting cpu time. If it hasn't then > + * this is a good indication some task is hogging the cpu > + */ > + duration = is_softlockup(touch_ts, this_cpu); > + if (unlikely(duration)) { > + /* only warn once */ > + if (warn & SOFTLOCKUP) > + return HRTIMER_RESTART; > + > + printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n", > + this_cpu, duration, > + current->comm, task_pid_nr(current)); > + print_modules(); > + print_irqtrace_events(current); > + if (regs) > + show_regs(regs); > + else > + dump_stack(); > + > + if (softlockup_panic) > + panic("softlockup: hung tasks"); > + __get_cpu_var(watchdog_warn) = warn | SOFTLOCKUP; > + } else > + __get_cpu_var(watchdog_warn) = warn & ~SOFTLOCKUP;
Note these watchdog_warn modifications are racy against the same that happens with HARDLOCKUP. You might clear what did the nmi.
The race is harmless enough that we don't care much I think, but that's why it would have make sense to separate watchdog_warn tracking space between both.
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