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SubjectRe: [PATCH] cpuset: adjust the lock sequence when rebuilding the sched domains.
Hi,

On 05/09/19 10:18, Chunyan Zhang wrote:
> From: Vincent Wang <vincent.wang@unisoc.com>
>
> A deadlock issue is found when executing a cpu hotplug stress test on
> android phones with cpuset and scheduil enabled.
>
> When CPUx is plugged out, the hotplug thread that calls cpu_down()
> will hold cpu_hotplug_lock and wait the thread cpuhp/x to finish
> hotplug. If the core is the last one in a cluster, cpuhp/x have to
> call cpuhp_cpufreq_offline() and the kernel thread sugov need to exit
> for schedutil governor. The exit of sugov need to hold
> cgroup_threadgroup_rwsem in exit_signals(). For example:
>
> PID: 150 TASK: ffffffc0b9cad080 CPU: 0 COMMAND: "sprdhotplug"
> #0 [ffffff8009fcb9d0] __switch_to at ffffff80080858f0
> #1 [ffffff8009fcb9f0] __schedule at ffffff80089f185c
> #2 [ffffff8009fcba80] schedule at ffffff80089f1b84
> #3 [ffffff8009fcbaa0] schedule_timeout at ffffff80089f5124
> #4 [ffffff8009fcbb40] wait_for_common at ffffff80089f2944
> #5 [ffffff8009fcbbe0] wait_for_completion at ffffff80089f29a4
> #6 [ffffff8009fcbc00] __cpuhp_kick_ap at ffffff80080ab030
> #7 [ffffff8009fcbc20] cpuhp_kick_ap_work at ffffff80080ab154
> #8 [ffffff8009fcbc70] _cpu_down at ffffff80089ee19c
> #9 [ffffff8009fcbcd0] cpu_down at ffffff80080ac144
>
> PID: 26 TASK: ffffffc0bbe22080 CPU: 3 COMMAND: "cpuhp/3"
> #0 [ffffff8009693a30] __switch_to at ffffff80080858f0
> #1 [ffffff8009693a50] __schedule at ffffff80089f185c
> #2 [ffffff8009693ae0] schedule at ffffff80089f1b84
> #3 [ffffff8009693b00] schedule_timeout at ffffff80089f5124
> #4 [ffffff8009693ba0] wait_for_common at ffffff80089f2944
> #5 [ffffff8009693c40] wait_for_completion at ffffff80089f29a4
> #6 [ffffff8009693c60] kthread_stop at ffffff80080ccd2c
> #7 [ffffff8009693c90] sugov_exit at ffffff8008102134
> #8 [ffffff8009693cc0] cpufreq_exit_governor at ffffff80086c03bc
> #9 [ffffff8009693ce0] cpufreq_offline at ffffff80086c0634
>
> PID: 13819 TASK: ffffffc0affb6080 CPU: 0 COMMAND: "sugov:3"
> #0 [ffffff800ee73c30] __switch_to at ffffff80080858f0
> #1 [ffffff800ee73c50] __schedule at ffffff80089f185c
> #2 [ffffff800ee73ce0] schedule at ffffff80089f1b84
> #3 [ffffff800ee73d00] rwsem_down_read_failed at ffffff80089f49d0
> #4 [ffffff800ee73d80] __percpu_down_read at ffffff8008102ebc
> #5 [ffffff800ee73da0] exit_signals at ffffff80080bbd24
> #6 [ffffff800ee73de0] do_exit at ffffff80080ae65c
> #7 [ffffff800ee73e60] kthread at ffffff80080cc550
>
> Sometimes cgroup_threadgroup_rwsem is hold by another thread, for
> example Binder:681_2 on android, it wants to hold cpuset_mutex:
>
> PID: 732 TASK: ffffffc09668b080 CPU: 2 COMMAND: "Binder:681_2"
> #0 [ffffff800cb7b8c0] __switch_to at ffffff80080858f0
> #1 [ffffff800cb7b8e0] __schedule at ffffff80089f185c
> #2 [ffffff800cb7b970] schedule at ffffff80089f1b84
> #3 [ffffff800cb7b990] schedule_preempt_disabled at ffffff80089f205c
> #4 [ffffff800cb7b9a0] __mutex_lock at ffffff80089f3118
> #5 [ffffff800cb7ba40] __mutex_lock_slowpath at ffffff80089f3230
> #6 [ffffff800cb7ba60] mutex_lock at ffffff80089f3278
> #7 [ffffff800cb7ba80] cpuset_can_attach at ffffff8008152f84
> #8 [ffffff800cb7bae0] cgroup_migrate_execute at ffffff800814ada8
>
> On android, a thread kworker/3:0 will hold cpuset_mutex in
> rebuild_sched_domains() and want to hold cpu_hotplug_lock which
> is already hold by the hotplug thread.
>
> PID: 4847 TASK: ffffffc031a6a080 CPU: 3 COMMAND: "kworker/3:0"
> #0 [ffffff8016fd3ad0] __switch_to at ffffff80080858f0
> #1 [ffffff8016fd3af0] __schedule at ffffff80089f185c
> #2 [ffffff8016fd3b80] schedule at ffffff80089f1b84
> #3 [ffffff8016fd3ba0] rwsem_down_read_failed at ffffff80089f49d0
> #4 [ffffff8016fd3c20] __percpu_down_read at ffffff8008102ebc
> #5 [ffffff8016fd3c40] cpus_read_lock at ffffff80080aa59c
> #6 [ffffff8016fd3c50] rebuild_sched_domains_locked at ffffff80081522a8
>
> In order to fix the deadlock, this patch will adjust the lock sequence
> when rebuilding sched domains. After stress tests, it works well.
>
> Signed-off-by: Vincent Wang <vincent.wang@unisoc.com>
> Signed-off-by: Chunyan Zhang <zhang.lyra@gmail.com>
> ---
> kernel/cgroup/cpuset.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 5aa37531ce76..ef10d276da22 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -912,7 +912,6 @@ static void rebuild_sched_domains_locked(void)
> int ndoms;
>
> lockdep_assert_held(&cpuset_mutex);
> - get_online_cpus();
>
> /*
> * We have raced with CPU hotplug. Don't do anything to avoid
> @@ -921,19 +920,17 @@ static void rebuild_sched_domains_locked(void)
> */
> if (!top_cpuset.nr_subparts_cpus &&
> !cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask))
> - goto out;
> + return;
>
> if (top_cpuset.nr_subparts_cpus &&
> !cpumask_subset(top_cpuset.effective_cpus, cpu_active_mask))
> - goto out;
> + return;
>
> /* Generate domain masks and attrs */
> ndoms = generate_sched_domains(&doms, &attr);
>
> /* Have scheduler rebuild the domains */
> partition_sched_domains(ndoms, doms, attr);
> -out:
> - put_online_cpus();
> }
> #else /* !CONFIG_SMP */
> static void rebuild_sched_domains_locked(void)
> @@ -943,9 +940,11 @@ static void rebuild_sched_domains_locked(void)
>
> void rebuild_sched_domains(void)
> {
> + get_online_cpus();
> mutex_lock(&cpuset_mutex);
> rebuild_sched_domains_locked();
> mutex_unlock(&cpuset_mutex);
> + put_online_cpus();
> }

This looks a subset of d74b27d63a8b ("cgroup/cpuset: Change cpuset_rwsem
and hotplug lock order") from

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched/core

right?

Cc-ing Peter for reference.

Best,

Juri

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