FAILED: patch "[PATCH] sched/core: Make core-sched flips wait for in-flight" failed to apply to 5.15-stable tree

index 84ef83316562..0130463798f8 100644
@@ -443,6 +443,17 @@ static void __sched_core_flip(bool enabled)
 
 		sched_core_lock(cpu, &flags);
 
+		/*
+		 * A core-wide selection may have the shared rq lock temporarily
+		 * released by a lock-dropping ->pick_task(). Flipping would
+		 * rebind rq_lockp() under it. Wait it out.
+		 */
+		while (cpu_rq(cpu)->core->core_pick_in_flight) {
+			sched_core_unlock(cpu, &flags);
+			cpu_relax();
+			sched_core_lock(cpu, &flags);
+		}
+
 		for_each_cpu(t, smt_mask)
 			cpu_rq(t)->core_enabled = enabled;
 

@@ -6236,6 +6247,8 @@ pick_next_task(struct rq *rq, struct rq_flags *rf)
 		return __pick_next_task(rq, rf);
 	}
 
+	rq->core->core_pick_in_flight++;
+
 	/*
 	 * If there were no {en,de}queues since we picked (IOW, the task
 	 * pointers are all still valid), and we haven't scheduled the last

@@ -6450,6 +6463,7 @@ pick_next_task(struct rq *rq, struct rq_flags *rf)
 	}
 
 out_set_next:
+	rq->core->core_pick_in_flight--;
 	put_prev_set_next_task(rq, rq->donor, next);
 	if (rq->core->core_forceidle_count && next == rq->idle)
 		queue_core_balance(rq);

@@ -6644,6 +6658,13 @@ static void sched_core_cpu_deactivate(unsigned int cpu)
 	core_rq->core_forceidle_seq        = rq->core_forceidle_seq;
 	core_rq->core_forceidle_occupation = rq->core_forceidle_occupation;
 
+	/*
+	 * A stale leftover would bias the count forever if this CPU later
+	 * returns as its own leader. Move, don't copy.
+	 */
+	core_rq->core_pick_in_flight       = rq->core_pick_in_flight;
+	rq->core_pick_in_flight            = 0;
+
 	/*
 	 * Accounting edge for forced idle is handled in pick_next_task().
 	 * Don't need another one here, since the hotplug thread shouldn't

@@ -9060,6 +9081,7 @@ void __init sched_init(void)
 		rq->core_forceidle_count = 0;
 		rq->core_forceidle_occupation = 0;
 		rq->core_forceidle_start = 0;
+		rq->core_pick_in_flight = 0;
 
 		rq->core_cookie = 0UL;
 #endif

index 56acf502ba26..450b6a04669f 100644
@@ -1358,6 +1358,7 @@ struct rq {
 	unsigned int		core_forceidle_seq;
 	unsigned int		core_forceidle_occupation;
 	u64			core_forceidle_start;
+	unsigned int		core_pick_in_flight;
 #endif /* CONFIG_SCHED_CORE */
 
 	/* Scratch cpumask to be temporarily used under rq_lock */

index c4e9fac7507a9..22a34f826093a 100644
@@ -274,6 +274,17 @@ static void __sched_core_flip(bool enabled)
 
 		sched_core_lock(cpu, &flags);
 
+		/*
+		 * A core-wide selection may have the shared rq lock temporarily
+		 * released by a lock-dropping ->pick_task(). Flipping would
+		 * rebind rq_lockp() under it. Wait it out.
+		 */
+		while (cpu_rq(cpu)->core->core_pick_in_flight) {
+			sched_core_unlock(cpu, &flags);
+			cpu_relax();
+			sched_core_lock(cpu, &flags);
+		}
+
 		for_each_cpu(t, smt_mask)
 			cpu_rq(t)->core_enabled = enabled;
 

@@ -5789,6 +5800,8 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 		return __pick_next_task(rq, prev, rf);
 	}
 
+	rq->core->core_pick_in_flight++;
+
 	/*
 	 * If there were no {en,de}queues since we picked (IOW, the task
 	 * pointers are all still valid), and we haven't scheduled the last

@@ -5810,6 +5823,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 		}
 
 		rq->core_pick = NULL;
+		rq->core->core_pick_in_flight--;
 		return next;
 	}
 

@@ -5992,6 +6006,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 	}
 
 done:
+	rq->core->core_pick_in_flight--;
 	set_next_task(rq, next);
 	return next;
 }

@@ -6181,6 +6196,13 @@ static void sched_core_cpu_deactivate(unsigned int cpu)
 	core_rq->core_forceidle     = rq->core_forceidle;
 	core_rq->core_forceidle_seq = rq->core_forceidle_seq;
 
+	/*
+	 * A stale leftover would bias the count forever if this CPU later
+	 * returns as its own leader. Move, don't copy.
+	 */
+	core_rq->core_pick_in_flight       = rq->core_pick_in_flight;
+	rq->core_pick_in_flight            = 0;
+
 	/* install new leader */
 	for_each_cpu(t, smt_mask) {
 		rq = cpu_rq(t);

@@ -9551,6 +9573,7 @@ void __init sched_init(void)
 		rq->core_enabled = 0;
 		rq->core_tree = RB_ROOT;
 		rq->core_forceidle = false;
+		rq->core_pick_in_flight = 0;
 
 		rq->core_cookie = 0UL;
 #endif

index f58040a51e334..cb89d36146a63 100644
@@ -1110,6 +1110,7 @@ struct rq {
 	unsigned long		core_cookie;
 	unsigned char		core_forceidle;
 	unsigned int		core_forceidle_seq;
+	unsigned int		core_pick_in_flight;
 #endif
 };