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Date: Wed, 1 Nov 2017 14:11:27 -0400 From: Don Zickus <dzickus@...hat.com> To: Guenter Roeck <linux@...ck-us.net> Cc: Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org> Subject: Re: Crashes in perf_event_ctx_lock_nested On Tue, Oct 31, 2017 at 03:11:07PM -0700, 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@...ck-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 ? I switched it to atomic and it solves that problem. The functionality isn't broken currently, just the informational message. Patch attached to try. 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> #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); } }
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