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Message-ID: <20260206203712.1989610-3-longman@redhat.com>
Date: Fri, 6 Feb 2026 15:37:10 -0500
From: Waiman Long <longman@...hat.com>
To: Chen Ridong <chenridong@...weicloud.com>,
Tejun Heo <tj@...nel.org>,
Johannes Weiner <hannes@...xchg.org>,
Michal Koutný <mkoutny@...e.com>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>,
Mel Gorman <mgorman@...e.de>,
Valentin Schneider <vschneid@...hat.com>,
Anna-Maria Behnsen <anna-maria@...utronix.de>,
Frederic Weisbecker <frederic@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Shuah Khan <shuah@...nel.org>
Cc: cgroups@...r.kernel.org,
linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org,
Waiman Long <longman@...hat.com>
Subject: [PATCH/for-next v4 2/4] cgroup/cpuset: Defer housekeeping_update() calls from CPU hotplug to workqueue
The update_isolation_cpumasks() function can be called either directly
from regular cpuset control file write with cpuset_full_lock() called
or via the CPU hotplug path with cpus_write_lock and cpuset_mutex held.
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 actual housekeeping_update() call, if needed, will happen after
cpus_write_lock is released.
We can't use the synchronous task_work API as call from CPU hotplug
path happen in the per-cpu kthread of the CPU that is being shut down
or brought up. Because of the asynchronous nature of workqueue, the
HK_TYPE_DOMAIN housekeeping cpumask will be updated a bit later than the
"cpuset.cpus.isolated" control file in this case.
Also add a check in test_cpuset_prs.sh and modify some existing
test cases to confirm that "cpuset.cpus.isolated" and HK_TYPE_DOMAIN
housekeeping cpumask will both be updated.
Signed-off-by: Waiman Long <longman@...hat.com>
---
kernel/cgroup/cpuset.c | 41 +++++++++++++++++--
.../selftests/cgroup/test_cpuset_prs.sh | 13 ++++--
2 files changed, 48 insertions(+), 6 deletions(-)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index a4c6386a594d..eb0eabd85e8c 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1302,6 +1302,17 @@ static bool prstate_housekeeping_conflict(int prstate, struct cpumask *new_cpus)
return false;
}
+static void isolcpus_workfn(struct work_struct *work)
+{
+ cpuset_full_lock();
+ if (isolated_cpus_updating) {
+ isolated_cpus_updating = false;
+ WARN_ON_ONCE(housekeeping_update(isolated_cpus) < 0);
+ rebuild_sched_domains_locked();
+ }
+ cpuset_full_unlock();
+}
+
/*
* update_isolation_cpumasks - Update external isolation related CPU masks
*
@@ -1310,14 +1321,38 @@ 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);
+ lockdep_assert_cpuset_lock_held();
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) {
+ /*
+ * 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
+ * isolcpus_workfn() is invoked to process the previously
+ * queued work. Since isolcpus_workfn() doesn't use the work
+ * item at all, this is not a problem.
+ */
+ queue_work(system_unbound_wq, &isolcpus_work);
+ return;
+ }
+ WARN_ON_ONCE(housekeeping_update(isolated_cpus) < 0);
isolated_cpus_updating = false;
}
diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
index 5dff3ad53867..0502b156582b 100755
--- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
+++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
@@ -245,8 +245,9 @@ TEST_MATRIX=(
"C2-3:P1:S+ C3:P2 . . O2=0 O2=1 . . 0 A1:2|A2:3 A1:P1|A2:P2"
"C2-3:P1:S+ C3:P1 . . O2=0 . . . 0 A1:|A2:3 A1:P1|A2:P1"
"C2-3:P1:S+ C3:P1 . . O3=0 . . . 0 A1:2|A2: A1:P1|A2:P1"
- "C2-3:P1:S+ C3:P1 . . T:O2=0 . . . 0 A1:3|A2:3 A1:P1|A2:P-1"
- "C2-3:P1:S+ C3:P1 . . . T:O3=0 . . 0 A1:2|A2:2 A1:P1|A2:P-1"
+ "C2-3:P1:S+ C3:P2 . . T:O2=0 . . . 0 A1:3|A2:3 A1:P1|A2:P-2"
+ "C1-3:P1:S+ C3:P2 . . . T:O3=0 . . 0 A1:1-2|A2:1-2 A1:P1|A2:P-2 3|"
+ "C1-3:P1:S+ 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"
@@ -764,7 +765,7 @@ 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
#
@@ -773,6 +774,7 @@ 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 [[ $EXPECTED_ISOLCPUS = . ]]
@@ -810,6 +812,11 @@ check_isolcpus()
ISOLCPUS=
EXPECTED_ISOLCPUS=$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
#
--
2.52.0
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