diff --git a/kernel/sched/core.c b/kernel/sched/core.c index b64f163d512c..7063c6a07440 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1946,6 +1946,25 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) goto stat; #ifdef CONFIG_SMP + /* + * Ensure we load p->on_cpu _after_ p->on_rq, otherwise it would be + * possible to, falsely, observe p->on_cpu == 0. + * + * One must be running (->on_cpu == 1) in order to remove oneself + * from the runqueue. + * + * [S] ->on_cpu = 1; [L] ->on_rq + * UNLOCK rq->lock + * RMB + * LOCK rq->lock + * [S] ->on_rq = 0; [L] ->on_cpu + * + * Pairs with the full barrier implied in the UNLOCK+LOCK on rq->lock + * from the consecutive calls to schedule(); the first switching to our + * task, the second putting it to sleep. + */ + smp_rmb(); + /* * If the owning (remote) cpu is still in the middle of schedule() with * this task as prev, wait until its done referencing the task.