On Fri, Jan 08, 2021 at 08:55:27PM +0800, Lecopzer Chen wrote: > > On Mon, 21 Dec 2020 at 21:53, Lecopzer Chen <[email protected]> > > wrote: > > > > > > commit 367c820ef08082 ("arm64: Enable perf events based hard lockup > > > detector") > > > reinitilizes lockup detector after arm64 PMU is initialized and open > > > a window for accessing smp_processor_id() in preemptible context. > > > Since hardlockup_detector_perf_init() always called in init stage > > > with a single cpu, but we initialize lockup detector after the init task > > > is migratable. > > > > > > Fix this by utilizing lockup detector reconfiguration which calls > > > softlockup_start_all() on each cpu and calls watatchdog_nmi_enable() > > > later. > > > Because softlockup_start_all() use IPI call function to make sure > > > watatchdog_nmi_enable() will bind on each cpu and fix this issue. > > > > IMO, this just creates unnecessary dependency for hardlockup detector > > init via softlockup detector (see the alternative definition of > > lockup_detector_reconfigure()). > > > The arm64/Kconfig select HAVE_HARDLOCKUP_DETECTOR_PERF if we have NMI: > select HAVE_HARDLOCKUP_DETECTOR_PERF if PERF_EVENTS && > HAVE_PERF_EVENTS_NMI > > And in lib/Kconfig.debug HARDLOCKUP_DETECTOR select SOFTLOCKUP_DETECTOR > automatically. > config HARDLOCKUP_DETECTOR_PERF > bool > select SOFTLOCKUP_DETECTOR > > So we don't need to explicitly select softlockup. > And actually this patch is not a perfect solution like you said > (hardlockup depends on softlockup), > but the key point is that lockup_detector_init() seems only design for > using in early init stage and not for calling in later deffered initial > process.
I agree; the current usage in armv8_pmu_driver_init() looks very broken to me, and bodging it with raw_smp_processor_id() isn't the right solution. Maybe we should just revert 367c820ef08082, as this looks like a design issue rather than something with a simple fix? Will
