On 03/26, Thomas Gleixner wrote: > > The rework of the watchdog core to use cpu_stop_work broke the watchdog > cpumask on CPU hotplug. > > The watchdog_enable/disable() functions are now called unconditionally from > the hotplug callback, i.e. even on CPUs which are not in the watchdog > cpumask. > > Only invoke them when the plugged CPU is in the watchdog cpumask. > > Fixes: 9cf57731b63e ("watchdog/softlockup: Replace "watchdog/%u" threads with > cpu_stop_work") > Signed-off-by: Thomas Gleixner <t...@linutronix.de> > Cc: sta...@vger.kernel.org > --- > kernel/watchdog.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > --- a/kernel/watchdog.c > +++ b/kernel/watchdog.c > @@ -547,13 +547,15 @@ static void softlockup_start_all(void) > > int lockup_detector_online_cpu(unsigned int cpu) > { > - watchdog_enable(cpu); > + if (cpumask_test_cpu(cpu, &watchdog_allowed_mask)) > + watchdog_enable(cpu); > return 0; > } > > int lockup_detector_offline_cpu(unsigned int cpu) > { > - watchdog_disable(cpu); > + if (cpumask_test_cpu(cpu, &watchdog_allowed_mask)) > + watchdog_disable(cpu); > return 0; > }
IIUC without this fix an NMI watchdog can too be enabled at boot time even if the initial watchdog_cpumask = housekeeping_cpumask(HK_FLAG_TIMER) doesn't include the plugged CPU. And after that writing 0 to /proc/sys/kernel/nmi_watchdog clears NMI_WATCHDOG_ENABLED but this can't disable NMI watchdog's outside of watchdog_allowed_mask. So may be this can explain the problem reported by Maxime ? See https://lore.kernel.org/lkml/b99c5a25-a5fe-18dd-2f1d-bdd6834f0...@redhat.com/ Oleg.