diff options
| -rw-r--r-- | kernel/sched/fair.c | 35 |
1 files changed, 34 insertions, 1 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 06e77d60a510..61f88665baf3 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5447,10 +5447,22 @@ static int sched_group_energy(struct energy_env *eenv) { struct cpumask visit_cpus; u64 total_energy = 0; + int cpu_count; WARN_ON(!eenv->sg_top->sge); cpumask_copy(&visit_cpus, sched_group_cpus(eenv->sg_top)); + /* If a cpu is hotplugged in while we are in this function, + * it does not appear in the existing visit_cpus mask + * which came from the sched_group pointer of the + * sched_domain pointed at by sd_ea for either the prev + * or next cpu and was dereferenced in __energy_diff. + * Since we will dereference sd_scs later as we iterate + * through the CPUs we expect to visit, new CPUs can + * be present which are not in the visit_cpus mask. + * Guard this with cpu_count. + */ + cpu_count = cpumask_weight(&visit_cpus); while (!cpumask_empty(&visit_cpus)) { struct sched_group *sg_shared_cap = NULL; @@ -5460,6 +5472,8 @@ static int sched_group_energy(struct energy_env *eenv) /* * Is the group utilization affected by cpus outside this * sched_group? + * This sd may have groups with cpus which were not present + * when we took visit_cpus. */ sd = rcu_dereference(per_cpu(sd_scs, cpu)); @@ -5509,8 +5523,24 @@ static int sched_group_energy(struct energy_env *eenv) total_energy += sg_busy_energy + sg_idle_energy; - if (!sd->child) + if (!sd->child) { + /* + * cpu_count here is the number of + * cpus we expect to visit in this + * calculation. If we race against + * hotplug, we can have extra cpus + * added to the groups we are + * iterating which do not appear in + * the visit_cpus mask. In that case + * we are not able to calculate energy + * without restarting so we will bail + * out and use prev_cpu this time. + */ + if (!cpu_count) + return -EINVAL; cpumask_xor(&visit_cpus, &visit_cpus, sched_group_cpus(sg)); + cpu_count--; + } if (cpumask_equal(sched_group_cpus(sg), sched_group_cpus(eenv->sg_top))) goto next_cpu; @@ -5522,6 +5552,9 @@ static int sched_group_energy(struct energy_env *eenv) * If we raced with hotplug and got an sd NULL-pointer; * returning a wrong energy estimation is better than * entering an infinite loop. + * Specifically: If a cpu is unplugged after we took + * the visit_cpus mask, it no longer has an sd_scs + * pointer, so when we dereference it, we get NULL. */ if (cpumask_test_cpu(cpu, &visit_cpus)) return -EINVAL; |