sched: Mandate shared flags for sched_change

Shrikanth noted that sched_change pattern relies on using shared
flags.

Suggested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

kernel/sched/core.c

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e5ce213..3e6ac0c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -10783,6 +10783,12 @@ struct sched_change_ctx *sched_change_begin(struct task_struct *p, unsigned int
 	struct sched_change_ctx *ctx = this_cpu_ptr(&sched_change_ctx);
 	struct rq *rq = task_rq(p);
 
+	/*
+	 * Must exclusively use matched flags since this is both dequeue and
+	 * enqueue.
+	 */
+	WARN_ON_ONCE(flags & 0xFFFF0000);
+
 	lockdep_assert_rq_held(rq);
 
 	if (!(flags & DEQUEUE_NOCLOCK)) {