FAILED: patch "[PATCH] sched: Prevent balance_push() on remote runqueues" failed to apply to 5.13-stable tree

The patch below does not apply to the 5.13-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 868ad33bfa3bf39960982682ad3a0f8ebda1656e Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <[email protected]>
Date: Sat, 28 Aug 2021 15:55:52 +0200
Subject: [PATCH] sched: Prevent balance_push() on remote runqueues

sched_setscheduler() and rt_mutex_setprio() invoke the run-queue balance callback after changing priorities or the scheduling class of a task. The run-queue for which the callback is invoked can be local or remote.

That's not a problem for the regular rq::push_work which is serialized with a busy flag in the run-queue struct, but for the balance_push() work which is only valid to be invoked on the outgoing CPU that's wrong. It not only triggers the debug warning, but also leaves the per CPU variable push_work unprotected, which can result in double enqueues on the stop machine list.

Remove the warning and validate that the function is invoked on the outgoing CPU.

index f3b27c6c5153..b21a1857b75a 100644
@@ -8523,7 +8523,6 @@ static void balance_push(struct rq *rq)
 	struct task_struct *push_task = rq->curr;
 
 	lockdep_assert_rq_held(rq);
-	SCHED_WARN_ON(rq->cpu != smp_processor_id());
 
 	/*
 	 * Ensure the thing is persistent until balance_push_set(.on = false);

@@ -8531,9 +8530,10 @@ static void balance_push(struct rq *rq)
 	rq->balance_callback = &balance_push_callback;
 
 	/*
-	 * Only active while going offline.
+	 * Only active while going offline and when invoked on the outgoing
+	 * CPU.
 	 */
-	if (!cpu_dying(rq->cpu))
+	if (!cpu_dying(rq->cpu) || rq != this_rq())
 		return;
 
 	/*