sched: Deny self-issued __set_cpus_allowed_ptr() when migrate_disable()

  migrate_disable();
  set_cpus_allowed_ptr(current, {something excluding task_cpu(current)});
  affine_move_task(); <-- never returns

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20201013140116.26651-1-valentin.schneider@arm.com

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e92d7853057c23d683d4c6779ffaf4e9438761a5..88c6fcb3bb6543912bcb1ec70fd9ba2e4f1aa0a9 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2238,8 +2238,17 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
                goto out;
        }
 
-       if (!(flags & SCA_MIGRATE_ENABLE) && cpumask_equal(&p->cpus_mask, new_mask))
-               goto out;
+       if (!(flags & SCA_MIGRATE_ENABLE)) {
+               if (cpumask_equal(&p->cpus_mask, new_mask))
+                       goto out;
+
+               if (WARN_ON_ONCE(p == current &&
+                                is_migration_disabled(p) &&
+                                !cpumask_test_cpu(task_cpu(p), new_mask))) {
+                       ret = -EBUSY;
+                       goto out;
+               }
+       }
 
        /*
         * Picking a ~random cpu helps in cases where we are changing affinity