--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -36,10 +36,6 @@
  */
 #define MIN_WRITEBACK_PAGES	(4096UL >> (PAGE_SHIFT - 10))
 
-struct wb_completion {
-	atomic_t		cnt;
-};
-
 /*
  * Passed into wb_writeback(), essentially a subset of writeback_control
  */
@@ -61,19 +57,6 @@ struct wb_writeback_work {
 };
 
 /*
- * If one wants to wait for one or more wb_writeback_works, each work's
- * ->done should be set to a wb_completion defined using the following
- * macro.  Once all work items are issued with wb_queue_work(), the caller
- * can wait for the completion of all using wb_wait_for_completion().  Work
- * items which are waited upon aren't freed automatically on completion.
- */
-#define DEFINE_WB_COMPLETION_ONSTACK(cmpl)				\
-	struct wb_completion cmpl = {					\
-		.cnt		= ATOMIC_INIT(1),			\
-	}
-
-
-/*
  * If an inode is constantly having its pages dirtied, but then the
  * updates stop dirtytime_expire_interval seconds in the past, it's
  * possible for the worst case time between when an inode has its
@@ -182,7 +165,7 @@ static void finish_writeback_work(struct
 	if (work->auto_free)
 		kfree(work);
 	if (done && atomic_dec_and_test(&done->cnt))
-		wake_up_all(&wb->bdi->wb_waitq);
+		wake_up_all(done->waitq);
 }
 
 static void wb_queue_work(struct bdi_writeback *wb,
@@ -206,20 +189,18 @@ static void wb_queue_work(struct bdi_wri
 
 /**
  * wb_wait_for_completion - wait for completion of bdi_writeback_works
- * @bdi: bdi work items were issued to
  * @done: target wb_completion
  *
  * Wait for one or more work items issued to @bdi with their ->done field
- * set to @done, which should have been defined with
- * DEFINE_WB_COMPLETION_ONSTACK().  This function returns after all such
- * work items are completed.  Work items which are waited upon aren't freed
+ * set to @done, which should have been initialized with
+ * DEFINE_WB_COMPLETION().  This function returns after all such work items
+ * are completed.  Work items which are waited upon aren't freed
  * automatically on completion.
  */
-static void wb_wait_for_completion(struct backing_dev_info *bdi,
-				   struct wb_completion *done)
+void wb_wait_for_completion(struct wb_completion *done)
 {
 	atomic_dec(&done->cnt);		/* put down the initial count */
-	wait_event(bdi->wb_waitq, !atomic_read(&done->cnt));
+	wait_event(*done->waitq, !atomic_read(&done->cnt));
 }
 
 #ifdef CONFIG_CGROUP_WRITEBACK
@@ -854,7 +835,7 @@ static void bdi_split_work_to_wbs(struct
 restart:
 	rcu_read_lock();
 	list_for_each_entry_continue_rcu(wb, &bdi->wb_list, bdi_node) {
-		DEFINE_WB_COMPLETION_ONSTACK(fallback_work_done);
+		DEFINE_WB_COMPLETION(fallback_work_done, bdi);
 		struct wb_writeback_work fallback_work;
 		struct wb_writeback_work *work;
 		long nr_pages;
@@ -901,7 +882,7 @@ restart:
 		last_wb = wb;
 
 		rcu_read_unlock();
-		wb_wait_for_completion(bdi, &fallback_work_done);
+		wb_wait_for_completion(&fallback_work_done);
 		goto restart;
 	}
 	rcu_read_unlock();
@@ -2373,7 +2354,8 @@ static void wait_sb_inodes(struct super_
 static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
 				     enum wb_reason reason, bool skip_if_busy)
 {
-	DEFINE_WB_COMPLETION_ONSTACK(done);
+	struct backing_dev_info *bdi = sb->s_bdi;
+	DEFINE_WB_COMPLETION(done, bdi);
 	struct wb_writeback_work work = {
 		.sb			= sb,
 		.sync_mode		= WB_SYNC_NONE,
@@ -2382,14 +2364,13 @@ static void __writeback_inodes_sb_nr(str
 		.nr_pages		= nr,
 		.reason			= reason,
 	};
-	struct backing_dev_info *bdi = sb->s_bdi;
 
 	if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
 		return;
 	WARN_ON(!rwsem_is_locked(&sb->s_umount));
 
 	bdi_split_work_to_wbs(sb->s_bdi, &work, skip_if_busy);
-	wb_wait_for_completion(bdi, &done);
+	wb_wait_for_completion(&done);
 }
 
 /**
@@ -2451,7 +2432,8 @@ EXPORT_SYMBOL(try_to_writeback_inodes_sb
  */
 void sync_inodes_sb(struct super_block *sb)
 {
-	DEFINE_WB_COMPLETION_ONSTACK(done);
+	struct backing_dev_info *bdi = sb->s_bdi;
+	DEFINE_WB_COMPLETION(done, bdi);
 	struct wb_writeback_work work = {
 		.sb		= sb,
 		.sync_mode	= WB_SYNC_ALL,
@@ -2461,7 +2443,6 @@ void sync_inodes_sb(struct super_block *
 		.reason		= WB_REASON_SYNC,
 		.for_sync	= 1,
 	};
-	struct backing_dev_info *bdi = sb->s_bdi;
 
 	/*
 	 * Can't skip on !bdi_has_dirty() because we should wait for !dirty
@@ -2475,7 +2456,7 @@ void sync_inodes_sb(struct super_block *
 	/* protect against inode wb switch, see inode_switch_wbs_work_fn() */
 	bdi_down_write_wb_switch_rwsem(bdi);
 	bdi_split_work_to_wbs(bdi, &work, false);
-	wb_wait_for_completion(bdi, &done);
+	wb_wait_for_completion(&done);
 	bdi_up_write_wb_switch_rwsem(bdi);
 
 	wait_sb_inodes(sb);
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -67,6 +67,26 @@ enum wb_reason {
 	WB_REASON_MAX,
 };
 
+struct wb_completion {
+	atomic_t		cnt;
+	wait_queue_head_t	*waitq;
+};
+
+#define __WB_COMPLETION_INIT(_waitq)	\
+	(struct wb_completion){ .cnt = ATOMIC_INIT(1), .waitq = (_waitq) }
+
+/*
+ * If one wants to wait for one or more wb_writeback_works, each work's
+ * ->done should be set to a wb_completion defined using the following
+ * macro.  Once all work items are issued with wb_queue_work(), the caller
+ * can wait for the completion of all using wb_wait_for_completion().  Work
+ * items which are waited upon aren't freed automatically on completion.
+ */
+#define WB_COMPLETION_INIT(bdi)		__WB_COMPLETION_INIT(&(bdi)->wb_waitq)
+
+#define DEFINE_WB_COMPLETION(cmpl, bdi)	\
+	struct wb_completion cmpl = WB_COMPLETION_INIT(bdi)
+
 /*
  * For cgroup writeback, multiple wb's may map to the same blkcg.  Those
  * wb's can operate mostly independently but should share the congested
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -44,6 +44,8 @@ void wb_start_background_writeback(struc
 void wb_workfn(struct work_struct *work);
 void wb_wakeup_delayed(struct bdi_writeback *wb);
 
+void wb_wait_for_completion(struct wb_completion *done);
+
 extern spinlock_t bdi_lock;
 extern struct list_head bdi_list;
 
