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    SubjectRe: [PATCH 1/8] [watchdog] combine nmi_watchdog and softlockup
    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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