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Subject[PATCH 2/3] sched/fair: Fixes for capacity inversion detection
Date
Traversing the Perf Domains requires rcu_read_lock() to be held and is
conditional on sched_energy_enabled(). rcu_read_lock() is held while in
load_balance(), add an assert to ensure this is always the case.

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>
---
kernel/sched/fair.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 89dadaafc1ec..7c0dd57e562a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8856,16 +8856,22 @@ 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);

rq->cpu_capacity_inverted = 0;

+ SCHED_WARN_ON(!rcu_read_lock_held());
+
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);

--
2.25.1
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