Messages in this thread | | | From | Xuewen Yan <> | Date | Mon, 11 Jul 2022 15:21:28 +0800 | Subject | Re: [PATCH] sched/schedutil: Fix deadlock between cpuset and cpu hotplug when using schedutil |
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Hi all
This deadlock is inevitable, any comment?
On Tue, Jul 5, 2022 at 11:03 PM Xuewen Yan <xuewen.yan@unisoc.com> wrote: > > 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@unisoc.com> > Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com> > --- > 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 >
Thanks! BR
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