Re: Crashes in perf_event_ctx_lock_nested

Guenter Roeck
2017-11-01T18:34:19Z

On Wed, Nov 01, 2017 at 02:11:27PM -0400, Don Zickus wrote:
> >
> > Maybe watchdog_cpus needs to be atomic ?
>
> I switched it to atomic and it solves that problem. The functionality isn't
> broken currently, just the informational message.
>
> Patch attached to try.
>

Tested-by: Guenter Roeck <linux@roeck-us.net>

Thanks!
Guenter

> Cheers,
> Don
>
> ---8<--------------
>
> diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c
> index a7f137c1933a..8ee4da223b35 100644
> --- a/kernel/watchdog_hld.c
> +++ b/kernel/watchdog_hld.c
> @@ -14,6 +14,7 @@
> #include <linux/nmi.h>
> #include <linux/module.h>
> #include <linux/sched/debug.h>
> +#include <linux/atomic.h>

Alphabetical order, maybe ?

>
> #include <asm/irq_regs.h>
> #include <linux/perf_event.h>
> @@ -25,7 +26,7 @@ static DEFINE_PER_CPU(struct perf_event *, dead_event);
> static struct cpumask dead_events_mask;
>
> static unsigned long hardlockup_allcpu_dumped;
> -static unsigned int watchdog_cpus;
> +static atomic_t watchdog_cpus = ATOMIC_INIT(0);
>
> void arch_touch_nmi_watchdog(void)
> {
> @@ -189,7 +190,8 @@ void hardlockup_detector_perf_enable(void)
> if (hardlockup_detector_event_create())
> return;
>
> - if (!watchdog_cpus++)
> + /* use original value for check */
> + if (!atomic_fetch_inc(&watchdog_cpus))
> pr_info("Enabled. Permanently consumes one hw-PMU counter.\n");
>
> perf_event_enable(this_cpu_read(watchdog_ev));
> @@ -207,7 +209,7 @@ void hardlockup_detector_perf_disable(void)
> this_cpu_write(watchdog_ev, NULL);
> this_cpu_write(dead_event, event);
> cpumask_set_cpu(smp_processor_id(), &dead_events_mask);
> - watchdog_cpus--;
> + atomic_dec(&watchdog_cpus);
> }
> }
>