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Message-ID: <20260128044251.1229702-2-longman@redhat.com>
Date: Tue, 27 Jan 2026 23:42:50 -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 1/2] cgroup/cpuset: Defer housekeeping_update() call from CPU hotplug to task_work
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 cause deadlock. So we
have to defer any call to housekeeping_update() after the CPU hotplug
operation has finished. This can be done via the task_work_add(...,
TWA_RESUME) API where the actual housekeeping_update() call, if needed,
will happen right before existing back to userspace.
Since the HK_TYPE_DOMAIN housekeeping cpumask should now track the
changes in "cpuset.cpus.isolated", add a check in test_cpuset_prs.sh to
confirm that the CPU hotplug deferral, if needed, is working as expected.
Signed-off-by: Waiman Long <longman@...hat.com>
---
kernel/cgroup/cpuset.c | 49 ++++++++++++++++++-
.../selftests/cgroup/test_cpuset_prs.sh | 9 ++++
2 files changed, 56 insertions(+), 2 deletions(-)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 7b7d12ab1006..98c7cb732206 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -84,6 +84,10 @@ static cpumask_var_t isolated_cpus;
*/
static bool isolated_cpus_updating;
+/* Both cpuset_mutex and cpus_read_locked acquired */
+static bool cpuset_full_locked;
+static bool isolation_task_work_queued;
+
/*
* A flag to force sched domain rebuild at the end of an operation.
* It can be set in
@@ -285,10 +289,12 @@ void cpuset_full_lock(void)
{
cpus_read_lock();
mutex_lock(&cpuset_mutex);
+ cpuset_full_locked = true;
}
void cpuset_full_unlock(void)
{
+ cpuset_full_locked = false;
mutex_unlock(&cpuset_mutex);
cpus_read_unlock();
}
@@ -1285,25 +1291,64 @@ static bool prstate_housekeeping_conflict(int prstate, struct cpumask *new_cpus)
return false;
}
+static void __update_isolation_cpumasks(bool twork);
+static void isolation_task_work_fn(struct callback_head *cb)
+{
+ cpuset_full_lock();
+ __update_isolation_cpumasks(true);
+ cpuset_full_lock();
+}
+
/*
- * update_isolation_cpumasks - Update external isolation related CPU masks
+ * __update_isolation_cpumasks - Update external isolation related CPU masks
+ * @twork - set if call from isolation_task_work_fn()
*
* The following external CPU masks will be updated if necessary:
* - workqueue unbound cpumask
*/
-static void update_isolation_cpumasks(void)
+static void __update_isolation_cpumasks(bool twork)
{
int ret;
+ if (twork)
+ isolation_task_work_queued = false;
+
if (!isolated_cpus_updating)
return;
+ /*
+ * This function can be reached either directly from regular cpuset
+ * control file write (cpuset_full_locked) or via hotplug
+ * (cpus_write_lock && cpuset_mutex held). In the later case, we
+ * defer the housekeeping_update() call to a task_work to avoid
+ * the possibility of deadlock. The task_work will be run right
+ * before exiting back to userspace.
+ */
+ if (!cpuset_full_locked) {
+ static struct callback_head twork_cb;
+
+ if (!isolation_task_work_queued) {
+ init_task_work(&twork_cb, isolation_task_work_fn);
+ if (!task_work_add(current, &twork_cb, TWA_RESUME))
+ isolation_task_work_queued = true;
+ else
+ /* Current task shouldn't be exiting */
+ WARN_ON_ONCE(1);
+ }
+ return;
+ }
+
ret = housekeeping_update(isolated_cpus);
WARN_ON_ONCE(ret < 0);
isolated_cpus_updating = false;
}
+static inline void update_isolation_cpumasks(void)
+{
+ __update_isolation_cpumasks(false);
+}
+
/**
* rm_siblings_excl_cpus - Remove exclusive CPUs that are used by sibling cpusets
* @parent: Parent cpuset containing all siblings
diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
index 5dff3ad53867..af4a2532cb3e 100755
--- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
+++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
@@ -773,6 +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 [[ $EXPECTED_ISOLCPUS = . ]]
@@ -810,6 +811,14 @@ check_isolcpus()
ISOLCPUS=
EXPECTED_ISOLCPUS=$EXPECTED_SDOMAIN
+ #
+ # The inverse of HK_TYPE_DOMAIN cpumask in $HKICPUS should match $ISOLCPUS
+ #
+ [[ "$ISOLCPUS" != "$HKICPUS" ]] && {
+ echo "Housekeeping isolated CPUs mismatch - $HKICPUS"
+ return 1
+ }
+
#
# Use the sched domain in debugfs to check isolated CPUs, if available
#
--
2.52.0
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