Commit 6df415aa authored by Waiman Long's avatar Waiman Long Committed by Tejun Heo
Browse files

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



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: default avatarWaiman Long <longman@redhat.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 3bfe4796

kernel/cgroup/cpuset.c

+26 −5
Original line number Diff line number Diff line
@@ -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 @@ 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;
@@ -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);

}

tools/testing/selftests/cgroup/test_cpuset_prs.sh

+10 −1
Original line number Diff line number Diff line
@@ -245,6 +245,9 @@ TEST_MATRIX=( 
	"  C2-3:P1  C3:P1   .      .     O3=0    .      .      .     0 A1:2|A2: A1:P1|A2:P1"

	"  C2-3:P1  C3:P1   .      .    T:O2=0   .      .      .     0 A1:3|A2:3 A1:P1|A2:P-1"

	"  C2-3:P1  C3:P1   .      .      .    T:O3=0   .      .     0 A1:2|A2:2 A1:P1|A2:P-1"

	"  C2-3:P1  C3:P2   .      .    T:O2=0   .      .      .     0 A1:3|A2:3 A1:P1|A2:P-2"

	"  C1-3:P1  C3:P2   .      .      .    T:O3=0   .      .     0 A1:1-2|A2:1-2 A1:P1|A2:P-2 3|"

	"  C1-3:P1  C3:P2   .      .      .    T:O3=0  O3=1    .     0 A1:1-2|A2:3 A1:P1|A2:P2  3"

	"$SETUP_A123_PARTITIONS    .     O1=0    .      .      .     0 A1:|A2:2|A3:3 A1:P1|A2:P1|A3:P1"

	"$SETUP_A123_PARTITIONS    .     O2=0    .      .      .     0 A1:1|A2:|A3:3 A1:P1|A2:P1|A3:P1"

	"$SETUP_A123_PARTITIONS    .     O3=0    .      .      .     0 A1:1|A2:2|A3: A1:P1|A2:P1|A3:P1"
@@ -761,7 +764,7 @@ check_cgroup_states() 
# only CPUs in isolated partitions as well as those that are isolated at

# boot time.

#

# $1 - expected isolated cpu list(s) <isolcpus1>{,<isolcpus2>}

# $1 - expected isolated cpu list(s) <isolcpus1>{|<isolcpus2>}

# <isolcpus1> - expected sched/domains value

# <isolcpus2> - cpuset.cpus.isolated value = <isolcpus1> if not defined

#
@@ -770,6 +773,7 @@ check_isolcpus() 
	EXPECTED_ISOLCPUS=$1

	ISCPUS=${CGROUP2}/cpuset.cpus.isolated

	ISOLCPUS=$(cat $ISCPUS)

	HKICPUS=$(cat /sys/devices/system/cpu/isolated)

	LASTISOLCPU=

	SCHED_DOMAINS=/sys/kernel/debug/sched/domains

	if [[ $EXPECTED_ISOLCPUS = . ]]
@@ -807,6 +811,11 @@ check_isolcpus() 
	ISOLCPUS=

	EXPECTED_ISOLCPUS=$EXPECTED_SDOMAIN



	#

	# The inverse of HK_TYPE_DOMAIN cpumask in $HKICPUS should match $ISOLCPUS

	#

	[[ "$ISOLCPUS" != "$HKICPUS" ]] && return 1



	#

	# Use the sched domain in debugfs to check isolated CPUs, if available

	#