Re: [PATCH/for-next v3 2/3] cgroup/cpuset: Defer housekeeping_update() calls from CPU hotplug to workqueue

From: Waiman Long

Date: Mon Feb 02 2026 - 15:33:13 EST

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.

Thanks,
Longman