Re: Crashes in perf_event_ctx_lock_nested

Thomas Gleixner
2017-11-01T18:23:21Z

On Tue, 31 Oct 2017, Guenter Roeck wrote:
> On Tue, Oct 31, 2017 at 10:32:00PM +0100, Thomas Gleixner wrote:
>
> [ ...]
>
> > So we have to revert
> >
> > a33d44843d45 ("watchdog/hardlockup/perf: Simplify deferred event destroy")
> >
> > Patch attached.
> >
>
> Tested-by: Guenter Roeck <linux@roeck-us.net>
>
> There is still a problem. When running
>
> echo 6 > /proc/sys/kernel/watchdog_thresh
> echo 5 > /proc/sys/kernel/watchdog_thresh
>
> repeatedly, the message
>
> NMI watchdog: Enabled. Permanently consumes one hw-PMU counter.
>
> stops after a while (after ~10-30 iterations, with fluctuations).
> After adding trace messages into hardlockup_detector_perf_disable()
> and hardlockup_detector_perf_enable(), I see:
>
> hardlockup_detector_perf_disable: disable(0): Number of CPUs: 3
> hardlockup_detector_perf_disable: disable(1): Number of CPUs: 2
> hardlockup_detector_perf_disable: disable(2): Number of CPUs: 1
> hardlockup_detector_perf_disable: disable(3): Number of CPUs: 0
> ...
> hardlockup_detector_perf_disable: disable(0): Number of CPUs: 2
> hardlockup_detector_perf_disable: disable(1): Number of CPUs: 1
> hardlockup_detector_perf_disable: disable(2): Number of CPUs: 0
> hardlockup_detector_perf_disable: disable(3): Number of CPUs: -1
> ...
> hardlockup_detector_perf_enable: enable(1): Number of CPUs: -6
> hardlockup_detector_perf_enable: enable(3): Number of CPUs: -5
> hardlockup_detector_perf_enable: enable(2): Number of CPUs: -4
> hardlockup_detector_perf_enable: enable(0): Number of CPUs: -3
>
> Maybe watchdog_cpus needs to be atomic ?

Indeed.

Thanks,

tglx