Commit ca174c70 authored by Waiman Long's avatar Waiman Long Committed by Tejun Heo
Browse files

cgroup/cpuset: Call rebuild_sched_domains() directly in hotplug 

Besides deferring the call to housekeeping_update(), commit 6df415aa
("cgroup/cpuset: Defer housekeeping_update() calls from CPU hotplug
to workqueue") also defers the rebuild_sched_domains() call to
the workqueue. So a new offline CPU may still be in a sched domain
or new online CPU not showing up in the sched domains for a short
transition period. That could be a problem in some corner cases and
can be the cause of a reported test failure[1]. Fix it by calling
rebuild_sched_domains_cpuslocked() directly in hotplug as before. If
isolated partition invalidation or recreation is being done, the
housekeeping_update() call to update the housekeeping cpumasks will
still be deferred to a workqueue.

In commit 3bfe4796 ("cgroup/cpuset: Move
housekeeping_update()/rebuild_sched_domains() together"),
housekeeping_update() is called before rebuild_sched_domains() because
it needs to access the HK_TYPE_DOMAIN housekeeping cpumask. That is now
changed to use the static HK_TYPE_DOMAIN_BOOT cpumask as HK_TYPE_DOMAIN
cpumask is now changeable at run time.  As a result, we can move the
rebuild_sched_domains() call before housekeeping_update() with
the slight advantage that it will be done in the same cpus_read_lock
critical section without the possibility of interference by a concurrent
cpu hot add/remove operation.

As it doesn't make sense to acquire cpuset_mutex/cpuset_top_mutex after
calling housekeeping_update() and immediately release them again, move
the cpuset_full_unlock() operation inside update_hk_sched_domains()
and rename it to cpuset_update_sd_hk_unlock() to signify that it will
release the full set of locks.

[1] https://lore.kernel.org/lkml/1a89aceb-48db-4edd-a730-b445e41221fe@nvidia.com



Fixes: 6df415aa ("cgroup/cpuset: Defer housekeeping_update() calls from CPU hotplug to workqueue")
Tested-by: default avatarJon Hunter <jonathanh@nvidia.com>
Reviewed-by: default avatarChen Ridong <chenridong@huaweicloud.com>
Signed-off-by: default avatarWaiman Long <longman@redhat.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 5ee8dbf5

kernel/cgroup/cpuset.c

+31 −28
Original line number Diff line number Diff line
@@ -879,7 +879,7 @@ static int generate_sched_domains(cpumask_var_t **domains, 
	/*

	 * Cgroup v2 doesn't support domain attributes, just set all of them

	 * to SD_ATTR_INIT. Also non-isolating partition root CPUs are a

	 * subset of HK_TYPE_DOMAIN housekeeping CPUs.

	 * subset of HK_TYPE_DOMAIN_BOOT housekeeping CPUs.

	 */

	for (i = 0; i < ndoms; i++) {

		/*
@@ -888,7 +888,7 @@ static int generate_sched_domains(cpumask_var_t **domains, 
		 */

		if (!csa || csa[i] == &top_cpuset)

			cpumask_and(doms[i], top_cpuset.effective_cpus,

				    housekeeping_cpumask(HK_TYPE_DOMAIN));

				    housekeeping_cpumask(HK_TYPE_DOMAIN_BOOT));

		else

			cpumask_copy(doms[i], csa[i]->effective_cpus);

		if (dattr)
@@ -1329,17 +1329,22 @@ static bool prstate_housekeeping_conflict(int prstate, struct cpumask *new_cpus) 
}



/*

 * update_hk_sched_domains - Update HK cpumasks & rebuild sched domains

 * cpuset_update_sd_hk_unlock - Rebuild sched domains, update HK & unlock

 *

 * Update housekeeping cpumasks and rebuild sched domains if necessary.

 * This should be called at the end of cpuset or hotplug actions.

 * Update housekeeping cpumasks and rebuild sched domains if necessary and

 * then do a cpuset_full_unlock().

 * This should be called at the end of cpuset operation.

 */

static void update_hk_sched_domains(void)

static void cpuset_update_sd_hk_unlock(void)

	__releases(&cpuset_mutex)

	__releases(&cpuset_top_mutex)

{

	/* force_sd_rebuild will be cleared in rebuild_sched_domains_locked() */

	if (force_sd_rebuild)

		rebuild_sched_domains_locked();



	if (update_housekeeping) {

		/* Updating HK cpumasks implies rebuild sched domains */

		update_housekeeping = false;

		force_sd_rebuild = true;

		cpumask_copy(isolated_hk_cpus, isolated_cpus);



		/*
@@ -1350,22 +1355,19 @@ static void update_hk_sched_domains(void) 
		mutex_unlock(&cpuset_mutex);

		cpus_read_unlock();

		WARN_ON_ONCE(housekeeping_update(isolated_hk_cpus));

		cpus_read_lock();

		mutex_lock(&cpuset_mutex);

		mutex_unlock(&cpuset_top_mutex);

	} else {

		cpuset_full_unlock();

	}

	/* force_sd_rebuild will be cleared in rebuild_sched_domains_locked() */

	if (force_sd_rebuild)

		rebuild_sched_domains_locked();

}



/*

 * Work function to invoke update_hk_sched_domains()

 * Work function to invoke cpuset_update_sd_hk_unlock()

 */

static void hk_sd_workfn(struct work_struct *work)

{

	cpuset_full_lock();

	update_hk_sched_domains();

	cpuset_full_unlock();

	cpuset_update_sd_hk_unlock();

}



/**
@@ -3230,8 +3232,7 @@ ssize_t cpuset_write_resmask(struct kernfs_open_file *of, 


	free_cpuset(trialcs);

out_unlock:

	update_hk_sched_domains();

	cpuset_full_unlock();

	cpuset_update_sd_hk_unlock();

	if (of_cft(of)->private == FILE_MEMLIST)

		schedule_flush_migrate_mm();

	return retval ?: nbytes;
@@ -3338,8 +3339,7 @@ static ssize_t cpuset_partition_write(struct kernfs_open_file *of, char *buf, 
	cpuset_full_lock();

	if (is_cpuset_online(cs))

		retval = update_prstate(cs, val);

	update_hk_sched_domains();

	cpuset_full_unlock();

	cpuset_update_sd_hk_unlock();

	return retval ?: nbytes;

}
@@ -3513,8 +3513,7 @@ static void cpuset_css_killed(struct cgroup_subsys_state *css) 
	/* Reset valid partition back to member */

	if (is_partition_valid(cs))

		update_prstate(cs, PRS_MEMBER);

	update_hk_sched_domains();

	cpuset_full_unlock();

	cpuset_update_sd_hk_unlock();

}



static void cpuset_css_free(struct cgroup_subsys_state *css)
@@ -3923,11 +3922,13 @@ static void cpuset_handle_hotplug(void) 
		rcu_read_unlock();

	}





	/*

	 * 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.

	 * rebuild_sched_domains() will always be called directly if needed

	 * to make sure that newly added or removed CPU will be reflected in

	 * the sched domains. However, if isolated partition invalidation

	 * or recreation is being done (update_housekeeping set), a work item

	 * will be queued to call housekeeping_update() to update the

	 * corresponding housekeeping cpumasks after some slight delay.

	 *

	 * 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
@@ -3936,8 +3937,10 @@ static void cpuset_handle_hotplug(void) 
	 * 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);

	if (force_sd_rebuild)

		rebuild_sched_domains_cpuslocked();

	if (update_housekeeping)

		queue_work(system_dfl_wq, &hk_sd_work);



	free_tmpmasks(ptmp);

}