Le Sat, Feb 07, 2026 at 09:00:45PM -0500, Waiman Long a écrit : > On 2/6/26 5:28 PM, Frederic Weisbecker wrote: > > Le Fri, Feb 06, 2026 at 03:37:10PM -0500, Waiman Long a écrit : > > > The update_isolation_cpumasks() function can be called either directly > > > from regular cpuset control file write with cpuset_full_lock() called > > > or via the CPU hotplug path with cpus_write_lock and cpuset_mutex held. > > > > > > As we are going to enable dynamic update to the nozh_full housekeeping > > > cpumask (HK_TYPE_KERNEL_NOISE) soon with the help of CPU hotplug, > > > allowing the CPU hotplug path to call into housekeeping_update() directly > > > from update_isolation_cpumasks() will likely cause deadlock. So we > > Why do we need to call housekeeping_update() from hotplug? I would > > expect it to be called only when cpuset control file are written since > > housekeeping cpumask don't deal with online CPUs but with possible > > CPUs. > > It needs to call housekeeping_update() only in the special case where there > is only one active CPU in an isolated partition and that CPU goes offline. > In this case, the partition becomes disabled that causes change in the > isolated CPUs. I know this special case shouldn't happen in real world, but > I do have test case to test that.
But why is that needed? This isn't changing the mask of domain isolated CPUs. Only their onlineness. I mean timers, workqueue, kthreads all have their hotplug callbacks able to deal with that already. > Theoretically, we can add code to handle this special case to keep this > offline isolated CPU in a special pool without changing isolated_cpus and > hence HK_TYPE_DOMAIN cpumask. In this way, we shouldn't need to call > housekeeping_update() from CPU hotplug. I will probably do that as CPU > hotplug will be used when we make HK_TYPE_KERNEL_NOISE cpumask dynamic in > the near future. That doesn't look necessary. Thanks. -- Frederic Weisbecker SUSE Labs
