[PATCH] sched/fair: Don't migrate with src_cpu == dst_cpu

[Scott Wood]

Besides being a waste of time to try to move tasks to where they already
are, this avoids triggering the WARN_ON_ONCE(is_migration_disabled(p))
in set_task_cpu().

Signed-off-by: Scott Wood <sw...@redhat.com>
---
Patch is against tip/master.  Assertion was seen by running rteval on the
RT tree.

 kernel/sched/fair.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e7e21ac479a2..f443626164d4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7574,7 +7574,8 @@ int can_migrate_task(struct task_struct *p, struct lb_env 
*env)
 
                /* Prevent to re-select dst_cpu via env's CPUs: */
                for_each_cpu_and(cpu, env->dst_grpmask, env->cpus) {
-                       if (cpumask_test_cpu(cpu, p->cpus_ptr)) {
+                       if (cpu != env->src_cpu &&
+                           cpumask_test_cpu(cpu, p->cpus_ptr)) {
                                env->flags |= LBF_DST_PINNED;
                                env->new_dst_cpu = cpu;
                                break;
-- 
2.27.0