On Mon, Feb 02, 2026 at 03:32:03PM -0500, Waiman Long wrote:
> On 2/2/26 3:18 PM, Peter Zijlstra wrote:
> > On Mon, Feb 02, 2026 at 03:11:43PM -0500, Waiman Long wrote:
> >
> > > @@ -1310,14 +1321,34 @@ static bool prstate_housekeeping_conflict(int
> > > prstate, struct cpumask *new_cpus)
> > > */
> > > static void update_isolation_cpumasks(void)
> > > {
> > > - int ret;
> > > + static DECLARE_WORK(isolcpus_work, isolcpus_workfn);
> > > if (!isolated_cpus_updating)
> > > return;
> > > - ret = housekeeping_update(isolated_cpus);
> > > - WARN_ON_ONCE(ret < 0);
> > > + /*
> > > + * This function can be reached either directly from regular cpuset
> > > + * control file write or via CPU hotplug. In the latter case, it is
> > > + * the per-cpu kthread that calls cpuset_handle_hotplug() on behalf
> > > + * of the task that initiates CPU shutdown or bringup.
> > > + *
> > > + * To have better flexibility and prevent the possibility of deadlock
> > > + * when calling from CPU hotplug, we defer the housekeeping_update()
> > > + * call to after the current cpuset critical section has finished.
> > > + * This is done via workqueue.
> > > + */
> > > + if (current->flags & PF_KTHREAD) {
> > /* Serializes the static isolcpus_workfn. */
> > lockdep_assert_held(&cpuset_mutex);
>
> Do we require synchronization between the the queue_work() call and the
> execution of the work function? I thought it is not needed, but I may be
> wrong.
Well, something needs to ensure there aren't two threads trying to use
this one work thing at the same time, no?
