sched/fair: Fixes for capacity inversion detection

Traversing the Perf Domains requires rcu_read_lock() to be held and is
conditional on sched_energy_enabled(). Ensure right protections applied.

Also skip capacity inversion detection for our own pd; which was an
error.

Fixes: 44c7b80bffc3 ("sched/fair: Detect capacity inversion")
Reported-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20230112122708.330667-3-qyousef@layalina.io

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index be43731..0f87369 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8868,16 +8868,23 @@ static void update_cpu_capacity(struct sched_domain *sd, int cpu)
         *   * Thermal pressure will impact all cpus in this perf domain
         *     equally.
         */
-       if (static_branch_unlikely(&sched_asym_cpucapacity)) {
+       if (sched_energy_enabled()) {
                unsigned long inv_cap = capacity_orig - thermal_load_avg(rq);
-               struct perf_domain *pd = rcu_dereference(rq->rd->pd);
+               struct perf_domain *pd;
+
+               rcu_read_lock();
 
+               pd = rcu_dereference(rq->rd->pd);
                rq->cpu_capacity_inverted = 0;
 
                for (; pd; pd = pd->next) {
                        struct cpumask *pd_span = perf_domain_span(pd);
                        unsigned long pd_cap_orig, pd_cap;
 
+                       /* We can't be inverted against our own pd */
+                       if (cpumask_test_cpu(cpu_of(rq), pd_span))
+                               continue;
+
                        cpu = cpumask_any(pd_span);
                        pd_cap_orig = arch_scale_cpu_capacity(cpu);
 
@@ -8902,6 +8909,8 @@ static void update_cpu_capacity(struct sched_domain *sd, int cpu)
                                break;
                        }
                }
+
+               rcu_read_unlock();
        }
 
        trace_sched_cpu_capacity_tp(rq);