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-rw-r--r--kernel/sched/core.c19
1 files changed, 19 insertions, 0 deletions
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
@@ -1947,6 +1947,25 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
#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.
*/