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 <[email protected]> --- kernel/cgroup/cpuset.c | 31 ++++++++++++++++--- .../selftests/cgroup/test_cpuset_prs.sh | 11 ++++++- 2 files changed, 36 insertions(+), 6 deletions(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 3d0d18bf182f..2c80bfc30bbc 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -1323,6 +1323,16 @@ 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 @@ -3795,6 +3805,7 @@ 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; @@ -3877,11 +3888,21 @@ 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); } diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh index 0c5db118f2d1..dc2dff361ec6 100755 --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh @@ -246,6 +246,9 @@ 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" @@ -762,7 +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 # @@ -771,6 +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 [[ $EXPECTED_ISOLCPUS = . ]] @@ -808,6 +812,11 @@ check_isolcpus() ISOLCPUS= EXPECTED_ISOLCPUS=$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 # -- 2.53.0
