On Mon, May 09, 2022 at 04:03:39PM +0200, Thomas Gleixner wrote: > On Thu, May 05 2022 at 17:00, Ricardo Neri wrote: > > + if (is_hpet_hld_interrupt(hdata)) { > > + /* > > + * Kick the timer first. If the HPET channel is periodic, it > > + * helps to reduce the delta between the expected TSC value and > > + * its actual value the next time the HPET channel fires. > > + */ > > + kick_timer(hdata, !(hdata->has_periodic)); > > + > > + if (cpumask_weight(hld_data->monitored_cpumask) > 1) { > > + /* > > + * Since we cannot know the source of an NMI, the best > > + * we can do is to use a flag to indicate to all online > > + * CPUs that they will get an NMI and that the source of > > + * that NMI is the hardlockup detector. Offline CPUs > > + * also receive the NMI but they ignore it. > > + * > > + * Even though we are in NMI context, we have concluded > > + * that the NMI came from the HPET channel assigned to > > + * the detector, an event that is infrequent and only > > + * occurs in the handling CPU. There should not be races > > + * with other NMIs. > > + */ > > + cpumask_copy(hld_data->inspect_cpumask, > > + cpu_online_mask); > > + > > + /* If we are here, IPI shorthands are enabled. */ > > + apic->send_IPI_allbutself(NMI_VECTOR); > > So if the monitored cpumask is a subset of online CPUs, which is the > case when isolation features are enabled, then you still send NMIs to > those isolated CPUs. I'm sure the isolation folks will be enthused.
Yes, I acknowledged this limitation in the cover letter. I should also update Documentation/admin-guide/lockup-watchdogs.rst. This patchset proposes the HPET NMI watchdog as an opt-in feature. Perhaps the limitation might be mitigated by adding a check for non-housekeeping and non-monitored CPUs in exc_nmi(). However, that will not eliminate the problem of isolated CPUs also getting the NMI. Thanks and BR, Ricardo