[PATCH] sched/schedutil: Fix deadlock between cpuset and cpu hotplug when using schedutil

From: Xuewen Yan
Date: Tue Jul 05 2022 - 09:19:57 EST

Next message: Dmitry Baryshkov: "Re: [PATCH 01/14] arm64: dts: qcom: sc7280: drop PCIe PHY clock index"
Previous message: Jason Gunthorpe: "Re: use-after-free in srpt_enable_tpg()"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

There is a deadlock between cpu_hotplug_lock sem and cgroup_threadgroup_rwsem.
And both cpu online and cpu offline scenarios will cause deadlock:

[1] cpu online:

1. first, thread-A get the cgroup_threadgroup_rwsem and waiting foe the cpu_hotplug_lock:

[ffffffc00f9c3850] __switch_to at ffffffc0081229d4
[ffffffc00f9c38b0] __schedule at ffffffc009c824f8
[ffffffc00f9c3910] schedule at ffffffc009c82b50
[ffffffc00f9c3970] percpu_rwsem_wait at ffffffc00828fbcc
[ffffffc00f9c39b0] __percpu_down_read at ffffffc008290180 <<< try to get cpu_hotplug_lock
[ffffffc00f9c39e0] cpus_read_lock at ffffffc0081dade8
[ffffffc00f9c3a20] cpuset_attach at ffffffc008366ed4
[ffffffc00f9c3a90] cgroup_migrate_execute at ffffffc00834f7d8
[ffffffc00f9c3b60] cgroup_attach_task at ffffffc0083539b8
[ffffffc00f9c3bd0] __cgroup1_procs_write at ffffffc00835f6ac <<< get the cgroup_threadgroup_rwsem
[ffffffc00f9c3c30] cgroup1_tasks_write at ffffffc00835f018
[ffffffc00f9c3c60] cgroup_file_write at ffffffc008348b04
[ffffffc00f9c3c90] kernfs_fop_write_iter at ffffffc0087544d8
[ffffffc00f9c3d50] vfs_write at ffffffc008607a8c
[ffffffc00f9c3db0] ksys_write at ffffffc0086076d8
[ffffffc00f9c3df0] __arm64_sys_write at ffffffc008607640
[ffffffc00f9c3e10] invoke_syscall at ffffffc00813dccc
[ffffffc00f9c3e30] el0_svc_common at ffffffc00813dbe4
[ffffffc00f9c3e70] do_el0_svc at ffffffc00813dac8
[ffffffc00f9c3e80] el0_svc at ffffffc0098836c8
[ffffffc00f9c3ea0] el0t_64_sync_handler at ffffffc00988363c
[ffffffc00f9c3fe0] el0t_64_sync at ffffffc008091e44

2. Thread-B get the cpu_hotplug_lock and waiting for cpuhp/x:

[ffffffc01245b740] __switch_to at ffffffc0081229d4
[ffffffc01245b7a0] __schedule at ffffffc009c824f8
[ffffffc01245b800] schedule at ffffffc009c82b50
[ffffffc01245b880] schedule_timeout at ffffffc009c8a144
[ffffffc01245b8e0] wait_for_common at ffffffc009c83dac <<< waiting for cpuhp/x complete
[ffffffc01245b940] cpuhp_kick_ap at ffffffc0081dc8ac <<< wake up cpuhp/x
[ffffffc01245b980] bringup_cpu at ffffffc0081db7f0
[ffffffc01245ba00] cpuhp_invoke_callback at ffffffc0081dc000
[ffffffc01245ba60] cpuhp_up_callbacks at ffffffc0081dd9b0
[ffffffc01245bac0] _cpu_up at ffffffc0081dd844 <<< percpu_down_write(&cpu_hotplug_lock)
[ffffffc01245bb40] cpu_up at ffffffc0081dd100
[ffffffc01245bb80] cpu_subsys_online at ffffffc008d8ebe4
[ffffffc01245bb90] device_online at ffffffc008d77dec
[ffffffc01245bbd0] online_store at ffffffc008d77bb8
[ffffffc01245bc30] dev_attr_store at ffffffc008d7c8b8
[ffffffc01245bc60] sysfs_kf_write at ffffffc008757894
[ffffffc01245bc90] kernfs_fop_write_iter at ffffffc0087544d8
[ffffffc01245bd50] vfs_write at ffffffc008607a8c
[ffffffc01245bdb0] ksys_write at ffffffc0086076d8
[ffffffc01245bdf0] __arm64_sys_write at ffffffc008607640
[ffffffc01245be10] invoke_syscall at ffffffc00813dccc
[ffffffc01245be30] el0_svc_common at ffffffc00813dc14
[ffffffc01245be70] do_el0_svc at ffffffc00813dac8
[ffffffc01245be80] el0_svc at ffffffc0098836c8
[ffffffc01245bea0] el0t_64_sync_handler at ffffffc00988363c
[ffffffc01245bfe0] el0t_64_sync at ffffffc008091e44

3. cpuhp/x would call cpufreq_online and the schedutil need create kthread, as a result it need wait for kthreadd:

[ffffffc00b653860] __switch_to at ffffffc0081229d4
[ffffffc00b6538c0] __schedule at ffffffc009c824f8
[ffffffc00b653920] schedule at ffffffc009c82b50
[ffffffc00b6539a0] schedule_timeout at ffffffc009c8a144
[ffffffc00b653a00] wait_for_common at ffffffc009c83dac <<< wait for kthreadd
[ffffffc00b653ad0] __kthread_create_on_node at ffffffc0082296b8
[ffffffc00b653b90] kthread_create_on_node at ffffffc008229a58
[ffffffc00b653bb0] sugov_init at ffffffc001d01414
[ffffffc00b653c00] cpufreq_init_governor at ffffffc009179a48
[ffffffc00b653c50] cpufreq_set_policy at ffffffc009179360
[ffffffc00b653cb0] cpufreq_online at ffffffc00917c3e4
[ffffffc00b653d10] cpuhp_cpufreq_online at ffffffc00917ee3c
[ffffffc00b653d70] cpuhp_invoke_callback at ffffffc0081dc000
[ffffffc00b653dd0] cpuhp_thread_fun at ffffffc0081df47c
[ffffffc00b653e10] smpboot_thread_fn at ffffffc008234718
[ffffffc00b653e70] kthread at ffffffc00822ac84

4. the kthreadd is trying to get cgroup_threadgroup_rwsem...

[ffffffc008073a70] __switch_to at ffffffc0081229d4
[ffffffc008073ad0] __schedule at ffffffc009c824f8
[ffffffc008073b30] schedule at ffffffc009c82b50
[ffffffc008073b90] percpu_rwsem_wait at ffffffc00828fbcc <<< cgroup_threadgroup_rwsem
[ffffffc008073bd0] __percpu_down_read at ffffffc008290180
[ffffffc008073c00] cgroup_css_set_fork at ffffffc008357ecc
[ffffffc008073c60] cgroup_can_fork at ffffffc008357bb4
[ffffffc008073d00] copy_process at ffffffc0081d18c4
[ffffffc008073d90] kernel_clone at ffffffc0081d088c
[ffffffc008073e50] kthreadd at ffffffc00822a8e4

Finally, the Thread-A and Thread-B would be blockd forever.

[2]cpu_offline:

1. first, thread-A get the cgroup_threadgroup_rwsem and waiting foe the cpu_hotplug_lock:

[ffffffc00f9c3850] __switch_to at ffffffc0081229d4
[ffffffc00f9c38b0] __schedule at ffffffc009c824f8
[ffffffc00f9c3910] schedule at ffffffc009c82b50
[ffffffc00f9c3970] percpu_rwsem_wait at ffffffc00828fbcc
[ffffffc00f9c39b0] __percpu_down_read at ffffffc008290180 <<< try to get cpu_hotplug_lock
[ffffffc00f9c39e0] cpus_read_lock at ffffffc0081dade8
[ffffffc00f9c3a20] cpuset_attach at ffffffc008366ed4
[ffffffc00f9c3a90] cgroup_migrate_execute at ffffffc00834f7d8
[ffffffc00f9c3b60] cgroup_attach_task at ffffffc0083539b8
[ffffffc00f9c3bd0] __cgroup1_procs_write at ffffffc00835f6ac <<< get the cgroup_threadgroup_rwsem
[ffffffc00f9c3c30] cgroup1_tasks_write at ffffffc00835f018
[ffffffc00f9c3c60] cgroup_file_write at ffffffc008348b04
[ffffffc00f9c3c90] kernfs_fop_write_iter at ffffffc0087544d8
[ffffffc00f9c3d50] vfs_write at ffffffc008607a8c
[ffffffc00f9c3db0] ksys_write at ffffffc0086076d8
[ffffffc00f9c3df0] __arm64_sys_write at ffffffc008607640
[ffffffc00f9c3e10] invoke_syscall at ffffffc00813dccc
[ffffffc00f9c3e30] el0_svc_common at ffffffc00813dbe4
[ffffffc00f9c3e70] do_el0_svc at ffffffc00813dac8
[ffffffc00f9c3e80] el0_svc at ffffffc0098836c8
[ffffffc00f9c3ea0] el0t_64_sync_handler at ffffffc00988363c
[ffffffc00f9c3fe0] el0t_64_sync at ffffffc008091e44

2. Thread-B get the cpu_hotplug_lock and waiting for cpuhp/x:

[ffffffc01245b740] __switch_to at ffffffc0081229d4
[ffffffc01245b7a0] __schedule at ffffffc009c824f8
[ffffffc01245b800] schedule at ffffffc009c82b50
[ffffffc01245b880] schedule_timeout at ffffffc009c8a144
[ffffffc01245b8e0] wait_for_common at ffffffc009c83dac <<< waiting for cpuhp/x complete
[ffffffc01245b940] cpuhp_kick_ap at ffffffc0081dc8ac <<< wake up cpuhp/x
[ffffffc01245b980] bringup_cpu at ffffffc0081db7f0
[ffffffc01245ba00] cpuhp_invoke_callback at ffffffc0081dc000
[ffffffc01245ba60] cpuhp_up_callbacks at ffffffc0081dd9b0
[ffffffc01245bac0] _cpu_up at ffffffc0081dd844 <<< percpu_down_write(&cpu_hotplug_lock)
[ffffffc01245bb40] cpu_up at ffffffc0081dd100
[ffffffc01245bb80] cpu_subsys_online at ffffffc008d8ebe4
[ffffffc01245bb90] device_online at ffffffc008d77dec
[ffffffc01245bbd0] online_store at ffffffc008d77bb8
[ffffffc01245bc30] dev_attr_store at ffffffc008d7c8b8
[ffffffc01245bc60] sysfs_kf_write at ffffffc008757894
[ffffffc01245bc90] kernfs_fop_write_iter at ffffffc0087544d8
[ffffffc01245bd50] vfs_write at ffffffc008607a8c
[ffffffc01245bdb0] ksys_write at ffffffc0086076d8
[ffffffc01245bdf0] __arm64_sys_write at ffffffc008607640
[ffffffc01245be10] invoke_syscall at ffffffc00813dccc
[ffffffc01245be30] el0_svc_common at ffffffc00813dc14
[ffffffc01245be70] do_el0_svc at ffffffc00813dac8
[ffffffc01245be80] el0_svc at ffffffc0098836c8
[ffffffc01245bea0] el0t_64_sync_handler at ffffffc00988363c
[ffffffc01245bfe0] el0t_64_sync at ffffffc008091e44

3.cpuhp/x would call cpufreq_offline and schedutil need stop_kthread:

[ffffffc00b683a60] __switch_to at ffffffc0081229d4
[ffffffc00b683ac0] __schedule at ffffffc009c824f8
[ffffffc00b683b20] schedule at ffffffc009c82b50
[ffffffc00b683ba0] schedule_timeout at ffffffc009c8a144
[ffffffc00b683c00] wait_for_common at ffffffc009c83dac <<< waiting for sugov complete
[ffffffc00b683c60] kthread_stop at ffffffc008228128 <<< wakeup sugov
[ffffffc00b683c90] sugov_exit at ffffffc001d016a8
[ffffffc00b683cc0] cpufreq_offline at ffffffc00917b4b8
[ffffffc00b683d10] cpuhp_cpufreq_offline at ffffffc00917ee70
[ffffffc00b683d70] cpuhp_invoke_callback at ffffffc0081dc000
[ffffffc00b683dd0] cpuhp_thread_fun at ffffffc0081df47c
[ffffffc00b683e10] smpboot_thread_fn at ffffffc008234718
[ffffffc00b683e70] kthread at ffffffc00822ac84

4. the sugov thread is waiting cgroup_threadgroup_rwsem:

[ffffffc01258bc10] __switch_to at ffffffc0081229d4
[ffffffc01258bc70] __schedule at ffffffc009c824f8
[ffffffc01258bcd0] schedule at ffffffc009c82b50
[ffffffc01258bd30] percpu_rwsem_wait at ffffffc00828fbcc <<< wait for cgroup_threadgroup_rwsem
[ffffffc01258bd70] __percpu_down_read at ffffffc008290180
[ffffffc01258bdb0] exit_signals at ffffffc0082074c8
[ffffffc01258be10] do_exit at ffffffc0081e5130
[ffffffc01258be70] kthread at ffffffc00822ac8c

Finally, the Thread-A and Thread-B would be blockd forever.

Combining the above two situations, the reason why Thread-A and Thread-B are blocked is because cpuhp/x is blocked.
If we can solve the problem that cpuhp is not blocked, Thread-A and Thread-B can run normally.
So we can let schedutil do not create or destory thread, so that the cpuhp/x would not be blocked.

So init the sugov thread just once to prevent the above deadlock.

Signed-off-by: Ke Wang <ke.wang@xxxxxxxxxx>
Signed-off-by: Xuewen Yan <xuewen.yan@xxxxxxxxxx>
---
kernel/sched/cpufreq_schedutil.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 285ad51caf0f..42d04a1eac20 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -8,6 +8,8 @@

#define IOWAIT_BOOST_MIN (SCHED_CAPACITY_SCALE / 8)

+static LIST_HEAD(sugov_list);
+
struct sugov_tunables {
struct gov_attr_set attr_set;
unsigned int rate_limit_us;
@@ -15,6 +17,7 @@ struct sugov_tunables {

struct sugov_policy {
struct cpufreq_policy *policy;
+ struct list_head sg_policy_list;

struct sugov_tunables *tunables;
struct list_head tunables_hook;
@@ -659,6 +662,7 @@ static int sugov_init(struct cpufreq_policy *policy)
struct sugov_policy *sg_policy;
struct sugov_tunables *tunables;
int ret = 0;
+ int sugov_init = 0;

/* State should be equivalent to EXIT */
if (policy->governor_data)
@@ -666,6 +670,13 @@ static int sugov_init(struct cpufreq_policy *policy)

cpufreq_enable_fast_switch(policy);

+ list_for_each_entry(sg_policy, &sugov_list, sg_policy_list) {
+ if (sg_policy->policy == policy) {
+ sugov_init = 1;
+ goto tunables_lock;
+ }
+ }
+
sg_policy = sugov_policy_alloc(policy);
if (!sg_policy) {
ret = -ENOMEM;
@@ -676,6 +687,10 @@ static int sugov_init(struct cpufreq_policy *policy)
if (ret)
goto free_sg_policy;

+ list_add(&sg_policy->sg_policy_list, &sugov_list);
+
+tunables_lock:
+
mutex_lock(&global_tunables_lock);

if (global_tunables) {
@@ -717,7 +732,8 @@ static int sugov_init(struct cpufreq_policy *policy)
sugov_clear_global_tunables();

stop_kthread:
- sugov_kthread_stop(sg_policy);
+ if (!sugov_init)
+ sugov_kthread_stop(sg_policy);
mutex_unlock(&global_tunables_lock);

free_sg_policy:
@@ -745,8 +761,14 @@ static void sugov_exit(struct cpufreq_policy *policy)

mutex_unlock(&global_tunables_lock);

+ list_for_each_entry(sg_policy, &sugov_list, sg_policy_list) {
+ if (sg_policy->policy == policy) {
+ goto out;
+ }
+ }
sugov_kthread_stop(sg_policy);
sugov_policy_free(sg_policy);
+out:
cpufreq_disable_fast_switch(policy);
}

--
2.25.1

Next message: Dmitry Baryshkov: "Re: [PATCH 01/14] arm64: dts: qcom: sc7280: drop PCIe PHY clock index"
Previous message: Jason Gunthorpe: "Re: use-after-free in srpt_enable_tpg()"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]