Le Sat, Feb 21, 2026 at 01:54:17PM -0500, Waiman Long a écrit : > The cpuset_handle_hotplug() may need to invoke housekeeping_update(), > for instance, when an isolated partition is invalidated because its > last active CPU has been put offline. > > 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.
I am a bit confused here. Why would CPU hotplug path need to call update_isolation_cpumasks() -> housekeeping_update() for HK_TYPE_KERNEL_NOISE? > So we > have to defer any call to housekeeping_update() after the CPU hotplug > operation has finished. This is now done via the workqueue where > the update_hk_sched_domains() function will be invoked via the > hk_sd_workfn(). > > An concurrent cpuset control file write may have executed the required > update_hk_sched_domains() function before the work function is called. So > the work function call may become a no-op when it is invoked. > > Signed-off-by: Waiman Long <[email protected]> > --- > kernel/cgroup/cpuset.c | 31 ++++++++++++++++--- > .../selftests/cgroup/test_cpuset_prs.sh | 11 ++++++- > 2 files changed, 36 insertions(+), 6 deletions(-) > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index 3d0d18bf182f..2c80bfc30bbc 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -1323,6 +1323,16 @@ static void update_hk_sched_domains(void) > rebuild_sched_domains_locked(); > } > > +/* > + * Work function to invoke update_hk_sched_domains() > + */ > +static void hk_sd_workfn(struct work_struct *work) > +{ > + cpuset_full_lock(); > + update_hk_sched_domains(); > + cpuset_full_unlock(); > +} > + > /** > * rm_siblings_excl_cpus - Remove exclusive CPUs that are used by sibling > cpusets > * @parent: Parent cpuset containing all siblings > @@ -3795,6 +3805,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset > *cs, struct tmpmasks *tmp) > */ > static void cpuset_handle_hotplug(void) > { > + static DECLARE_WORK(hk_sd_work, hk_sd_workfn); > static cpumask_t new_cpus; > static nodemask_t new_mems; > bool cpus_updated, mems_updated; > @@ -3877,11 +3888,21 @@ static void cpuset_handle_hotplug(void) > } > > > - if (update_housekeeping || force_sd_rebuild) { > - mutex_lock(&cpuset_mutex); > - update_hk_sched_domains(); > - mutex_unlock(&cpuset_mutex); > - } > + /* > + * Queue a work to call housekeeping_update() & rebuild_sched_domains() > + * There will be a slight delay before the HK_TYPE_DOMAIN housekeeping > + * cpumask can correctly reflect what is in isolated_cpus. > + * > + * We rely on WORK_STRUCT_PENDING_BIT to not requeue a work item that > + * is still pending. Before the pending bit is cleared, the work data > + * is copied out and work item dequeued. So it is possible to queue > + * the work again before the hk_sd_workfn() is invoked to process the > + * previously queued work. Since hk_sd_workfn() doesn't use the work > + * item at all, this is not a problem. > + */ > + if (update_housekeeping || force_sd_rebuild) > + queue_work(system_unbound_wq, &hk_sd_work); Nit about recent wq renames: s/system_unbound_wq/system_dfl_wq But what makes sure this work is executed by the end of the hotplug operations? Is there a risk for a stale hierarchy to be observed when it shouldn't? Or a stale housekeeping cpumask? Thanks. -- Frederic Weisbecker SUSE Labs
