Re: [BUG] CFS vs cpu hotplug

[Dmitry Adamushko <dmitry.adamushko@gmail.com>]

hm, while looking at this code again...


Ingo,

I think we may have a race between try_to_wake_up() and migrate_live_tasks() -> move_task_off_dead_cpu()
when the later one may end up looping endlessly.


Subject: sched: prevent a potentially endless loop in move_task_off_dead_cpu()

Interrupts are enabled on other CPUs when migration_call(CPU_DEAD, ...) is called so we may get a race
between try_to_wake_up() and migrate_live_tasks() -> move_task_off_dead_cpu(). The former one may push
a task out of a dead CPU causing the later one to loop endlessly.


Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>

---
diff --git a/kernel/sched.c b/kernel/sched.c
index 94ead43..9397b87 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5621,8 +5621,10 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
 
 	double_rq_lock(rq_src, rq_dest);
 	/* Already moved. */
-	if (task_cpu(p) != src_cpu)
+	if (task_cpu(p) != src_cpu) {
+		ret = 1;
 		goto out;
+	}
 	/* Affinity changed (again). */
 	if (!cpu_isset(dest_cpu, p->cpus_allowed))
 		goto out;

---