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cgroup/cpuset: Defer housekeeping_update() calls from CPU hotplug to workqueue

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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. 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 <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Waiman Long
2026-02-21 13:54:17 -05:00
committed by Tejun Heo
parent 3bfe479671
commit 6df415aa46
2 changed files with 36 additions and 6 deletions
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31
kernel/cgroup/cpuset.c
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@@ -1324,6 +1324,16 @@ 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
@@ -3796,6 +3806,7 @@ unlock:
*/
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;
@@ -3878,11 +3889,21 @@ 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);
free_tmpmasks(ptmp);
}