diff --git a/drivers/md/md.c b/drivers/md/md.c
index e02b18205d860df196015973b51291dd152d9663..a04485cdae296dfebdf06154ef4da1e347247374 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -690,6 +690,7 @@ void mddev_init(struct mddev *mddev)
 	mutex_init(&mddev->open_mutex);
 	mutex_init(&mddev->reconfig_mutex);
 	mutex_init(&mddev->bitmap_info.mutex);
+	mutex_init(&mddev->sync_mutex);
 	INIT_LIST_HEAD(&mddev->disks);
 	INIT_LIST_HEAD(&mddev->all_mddevs);
 	timer_setup(&mddev->safemode_timer, md_safemode_timeout, 0);
@@ -4885,14 +4886,18 @@ static void stop_sync_thread(struct mddev *mddev)
 
 static void idle_sync_thread(struct mddev *mddev)
 {
+	mutex_lock(&mddev->sync_mutex);
 	clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
 	stop_sync_thread(mddev);
+	mutex_unlock(&mddev->sync_mutex);
 }
 
 static void frozen_sync_thread(struct mddev *mddev)
 {
+	mutex_lock(&mddev->sync_mutex);
 	set_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
 	stop_sync_thread(mddev);
+	mutex_unlock(&mddev->sync_mutex);
 }
 
 static ssize_t
diff --git a/drivers/md/md.h b/drivers/md/md.h
index dbc566d309d666fde196a9860011bc4af48d4f78..50c7d3e4f2d7edbf7226aecc02da47b55d0137b8 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -528,6 +528,9 @@ struct mddev {
 	bool	has_superblocks:1;
 	bool	fail_last_dev:1;
 	bool	serialize_policy:1;
+
+	/* Used to synchronize idle and frozen for action_store() */
+	struct mutex sync_mutex;
 };
 
 enum recovery_flags {