On 9/6/22 16:01, Waiman Long wrote:
On 9/6/22 14:30, Tejun Heo wrote:
Hello,
(cc'ing Waiman in case he has a better idea)
On Mon, Sep 05, 2022 at 04:22:29PM +0800, Jing-Ting Wu wrote:
https://lore.kernel.org/lkml/YvrWaml3F+x9Dk+T@xxxxxxxxxxxxxxx/ is for
fix cgroup_threadgroup_rwsem <-> cpus_read_lock() deadlock.
But this issue is cgroup_threadgroup_rwsem <-> cpuset_rwsem deadlock.
If I'm understanding what you're writing correctly, this isn't a
deadlock.
The cpuset_hotplug_workfn simply isn't being woken up while holding
cpuset_rwsem and others are just waiting for that lock to be released.
I believe it is probably a bug in the scheduler core code.
__set_cpus_allowed_ptr_locked() calls affine_move_task() to move to a
random cpu within the new set allowable CPUs. However, if migration is
disabled, it shouldn't call affine_move_task() at all. Instead, I
would suggest that if the current cpu is within the new allowable
cpus, it should just skip doing affine_move_task(). Otherwise, it
should fail __set_cpus_allowed_ptr_locked().
Maybe like
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 838623b68031..5d9ea1553ec0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2794,9 +2794,9 @@ static int __set_cpus_allowed_ptr_locked(struct
task_struct *p,
if (cpumask_equal(&p->cpus_mask, new_mask))
goto out;
- if (WARN_ON_ONCE(p == current &&
- is_migration_disabled(p) &&
- !cpumask_test_cpu(task_cpu(p),
new_mask))) {
+ if (is_migration_disabled(p) &&
+ !cpumask_test_cpu(task_cpu(p), new_mask)) {
+ WARN_ON_ONCE(p == current);
ret = -EBUSY;
goto out;
}
@@ -2818,7 +2818,11 @@ static int __set_cpus_allowed_ptr_locked(struct
task_struct *p,
if (flags & SCA_USER)
user_mask = clear_user_cpus_ptr(p);
- ret = affine_move_task(rq, p, rf, dest_cpu, flags);
+ if (!is_migration_disabled(p) || (flags & SCA_MIGRATE_ENABLE)) {
+ ret = affine_move_task(rq, p, rf, dest_cpu, flags);
+ } else {
+ task_rq_unlock(rq, p, rf);
+ }
kfree(user_mask);
I haven't tested it myself, though.
Cheers,
Longman
