1 files changed, 32 insertions, 19 deletions

diff --git a/kernel/cpu.c b/kernel/cpu.c
index b03a32595cfe..acf5308fad51 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -271,11 +271,26 @@ void cpu_hotplug_enable(void)
 EXPORT_SYMBOL_GPL(cpu_hotplug_enable);
 #endif	/* CONFIG_HOTPLUG_CPU */
 
+static void __cpuhp_kick_ap_work(struct cpuhp_cpu_state *st);
+
 static int bringup_wait_for_ap(unsigned int cpu)
 {
 	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
 
+	/* Wait for the CPU to reach CPUHP_AP_ONLINE_IDLE */
 	wait_for_completion(&st->done);
+	if (WARN_ON_ONCE((!cpu_online(cpu))))
+		return -ECANCELED;
+
+	/* Unpark the stopper thread and the hotplug thread of the target cpu */
+	stop_machine_unpark(cpu);
+	kthread_unpark(st->thread);
+
+	/* Should we go further up ? */
+	if (st->target > CPUHP_AP_ONLINE_IDLE) {
+		__cpuhp_kick_ap_work(st);
+		wait_for_completion(&st->done);
+	}
 	return st->result;
 }
 
@@ -296,9 +311,7 @@ static int bringup_cpu(unsigned int cpu)
 	irq_unlock_sparse();
 	if (ret)
 		return ret;
-	ret = bringup_wait_for_ap(cpu);
-	BUG_ON(!cpu_online(cpu));
-	return ret;
+	return bringup_wait_for_ap(cpu);
 }
 
 /*
@@ -637,6 +650,7 @@ static int takedown_cpu(unsigned int cpu)
 	__cpu_die(cpu);
 
 	tick_cleanup_dead_cpu(cpu);
+	rcutree_migrate_callbacks(cpu);
 	return 0;
 }
 
@@ -767,31 +781,20 @@ void notify_cpu_starting(unsigned int cpu)
 }
 
 /*
- * Called from the idle task. We need to set active here, so we can kick off
- * the stopper thread and unpark the smpboot threads. If the target state is
- * beyond CPUHP_AP_ONLINE_IDLE we kick cpuhp thread and let it bring up the
- * cpu further.
+ * Called from the idle task. Wake up the controlling task which brings the
+ * stopper and the hotplug thread of the upcoming CPU up and then delegates
+ * the rest of the online bringup to the hotplug thread.
  */
 void cpuhp_online_idle(enum cpuhp_state state)
 {
 	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
-	unsigned int cpu = smp_processor_id();
 
 	/* Happens for the boot cpu */
 	if (state != CPUHP_AP_ONLINE_IDLE)
 		return;
 
 	st->state = CPUHP_AP_ONLINE_IDLE;
-
-	/* Unpark the stopper thread and the hotplug thread of this cpu */
-	stop_machine_unpark(cpu);
-	kthread_unpark(st->thread);
-
-	/* Should we go further up ? */
-	if (st->target > CPUHP_AP_ONLINE_IDLE)
-		__cpuhp_kick_ap_work(st);
-	else
-		complete(&st->done);
+	complete(&st->done);
 }
 
 /* Requires cpu_add_remove_lock to be held */
@@ -1250,7 +1253,17 @@ static int cpuhp_store_callbacks(enum cpuhp_state state, const char *name,
 	struct cpuhp_step *sp;
 	int ret = 0;
 
-	if (state == CPUHP_AP_ONLINE_DYN || state == CPUHP_BP_PREPARE_DYN) {
+	/*
+	 * If name is NULL, then the state gets removed.
+	 *
+	 * CPUHP_AP_ONLINE_DYN and CPUHP_BP_PREPARE_DYN are handed out on
+	 * the first allocation from these dynamic ranges, so the removal
+	 * would trigger a new allocation and clear the wrong (already
+	 * empty) state, leaving the callbacks of the to be cleared state
+	 * dangling, which causes wreckage on the next hotplug operation.
+	 */
+	if (name && (state == CPUHP_AP_ONLINE_DYN ||
+		     state == CPUHP_BP_PREPARE_DYN)) {
 		ret = cpuhp_reserve_state(state);
 		if (ret < 0)
 			return ret;