On Fri, Jun 19, 2015 at 10:58:36AM -0700, tip-bot for Alexander Shishkin wrote:
> @@ -371,12 +373,24 @@ int x86_add_exclusive(unsigned int what)
>
> out:
> mutex_unlock(&pmc_reserve_mutex);
> +
> + /*
> + * Assuming that all exclusive events will share the PMI handler
> + * (which checks active_events for whether there is work to do),
> + * we can bump active_events counter right here, except for
> + * x86_lbr_exclusive_lbr events that go through x86_pmu_event_init()
> + * path, which already bumps active_events for them.
> + */
> + if (!ret && what != x86_lbr_exclusive_lbr)
> + atomic_inc(&active_events);
> +
> return ret;
> }
>
> void x86_del_exclusive(unsigned int what)
> {
> atomic_dec(&x86_pmu.lbr_exclusive[what]);
> + atomic_dec(&active_events);
> }
>
This, conditional inc, unconditional dec.
This leads to active_events == 0 even though there's still the NMI
watchdog active generating NMIs.
I would say, drop the condition on inc, double inc isn't a problem as
long as we match with a double dec and that results in simpler code too.
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