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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
Download patch file Download diff file Expand all files Collapse all files

31
kernel/cgroup/cpuset.c
View file

@ -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);
}

11
tools/testing/selftests/cgroup/test_cpuset_prs.sh
View file

@ -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
#