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 <[email protected]> --- 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
