diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index ad955817916d00c35b6b41d204ec61013c88a10f..8fb3dcdebc80e943aff2bd272460d2ed1fb9aa12 100644
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -54,7 +54,9 @@ struct bdi_writeback_congested {
 	atomic_t refcnt;		/* nr of attached wb's and blkg */
 
 #ifdef CONFIG_CGROUP_WRITEBACK
-	struct backing_dev_info *bdi;	/* the associated bdi */
+	struct backing_dev_info *__bdi;	/* the associated bdi, set to NULL
+					 * on bdi unregistration. For memcg-wb
+					 * internal use only! */
 	int blkcg_id;			/* ID of the associated blkcg */
 	struct rb_node rb_node;		/* on bdi->cgwb_congestion_tree */
 #endif
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index c6f2a37028c205db8143ebe58677c790c66a0faf..12408f86783ccd40370c5b653f501924f735b65a 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -438,7 +438,7 @@ wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp)
 		return NULL;
 
 	atomic_set(&new_congested->refcnt, 0);
-	new_congested->bdi = bdi;
+	new_congested->__bdi = bdi;
 	new_congested->blkcg_id = blkcg_id;
 	goto retry;
 
@@ -466,10 +466,10 @@ void wb_congested_put(struct bdi_writeback_congested *congested)
 	}
 
 	/* bdi might already have been destroyed leaving @congested unlinked */
-	if (congested->bdi) {
+	if (congested->__bdi) {
 		rb_erase(&congested->rb_node,
-			 &congested->bdi->cgwb_congested_tree);
-		congested->bdi = NULL;
+			 &congested->__bdi->cgwb_congested_tree);
+		congested->__bdi = NULL;
 	}
 
 	spin_unlock_irqrestore(&cgwb_lock, flags);
@@ -752,7 +752,7 @@ static void cgwb_bdi_exit(struct backing_dev_info *bdi)
 			rb_entry(rbn, struct bdi_writeback_congested, rb_node);
 
 		rb_erase(rbn, &bdi->cgwb_congested_tree);
-		congested->bdi = NULL;	/* mark @congested unlinked */
+		congested->__bdi = NULL;	/* mark @congested unlinked */
 	}
 	spin_unlock_irq(&cgwb_lock);
 }