From: Vincent Wang <vincent.wang@xxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Chunyan Zhang <zhang.lyra@xxxxxxxxx>
---
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();
}
/**
--
2.20.1
