Re: [RFC PATCH v2 00/17] Core scheduling v2

[Vineeth Remanan Pillai <vpillai@digitalocean.com>]

> Thanks for pointing this out. I think the ideal fix would be to
> correctly initialize/cleanup the coresched attributes in the cpu
> hotplug code path so that lock could be taken successfully if the
> sibling is offlined/onlined after coresched was enabled. We are
> working on another bug related to hotplugpath and shall introduce
> the fix in v3.
>
A possible fix for handling the runqueues during cpu offline/online
is attached here with.

Thanks,
Vineeth

---
 kernel/sched/core.c | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e8e5f26db052..1a809849a1e7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -253,7 +253,7 @@ static int __sched_core_stopper(void *data)
 	bool enabled = !!(unsigned long)data;
 	int cpu;
 
-	for_each_possible_cpu(cpu)
+	for_each_online_cpu(cpu)
 		cpu_rq(cpu)->core_enabled = enabled;
 
 	return 0;
@@ -3764,6 +3764,9 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 			struct rq *rq_i = cpu_rq(i);
 			struct task_struct *p;
 
+			if (cpu_is_offline(i))
+				continue;
+
 			if (rq_i->core_pick)
 				continue;
 
@@ -3866,6 +3869,9 @@ next_class:;
 	for_each_cpu(i, smt_mask) {
 		struct rq *rq_i = cpu_rq(i);
 
+		if (cpu_is_offline(i))
+			continue;
+
 		WARN_ON_ONCE(!rq_i->core_pick);
 
 		rq_i->core_pick->core_occupation = occ;
@@ -6410,8 +6416,14 @@ int sched_cpu_activate(unsigned int cpu)
 	/*
 	 * When going up, increment the number of cores with SMT present.
 	 */
-	if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
+	if (cpumask_weight(cpu_smt_mask(cpu)) == 2) {
 		static_branch_inc_cpuslocked(&sched_smt_present);
+#ifdef CONFIG_SCHED_CORE
+		if (static_branch_unlikely(&__sched_core_enabled)) {
+			rq->core_enabled = true;
+		}
+#endif
+	}
 #endif
 	set_cpu_active(cpu, true);
 
@@ -6459,8 +6471,15 @@ int sched_cpu_deactivate(unsigned int cpu)
 	/*
 	 * When going down, decrement the number of cores with SMT present.
 	 */
-	if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
+	if (cpumask_weight(cpu_smt_mask(cpu)) == 2) {
+#ifdef CONFIG_SCHED_CORE
+		struct rq *rq = cpu_rq(cpu);
+		if (static_branch_unlikely(&__sched_core_enabled)) {
+			rq->core_enabled = false;
+		}
+#endif
 		static_branch_dec_cpuslocked(&sched_smt_present);
+	}
 #endif
 
 	if (!sched_smp_initialized)
@@ -6537,6 +6556,9 @@ int sched_cpu_dying(unsigned int cpu)
 	update_max_interval();
 	nohz_balance_exit_idle(rq);
 	hrtick_clear(rq);
+#ifdef CONFIG_SCHED_CORE
+	rq->core = NULL;
+#endif
 	return 0;
 }
 #endif
-- 
2.17.1