writeback: only use bdi_writeback_all() for WB_SYNC_NONE writeout

Data integrity writeback must use bdi_start_writeback() and ensure
that wbc->sb and wbc->bdi are set.
Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

fs/fs-writeback.c

@@ -50,7 +50,6 @@ struct wb_writeback_args {
  */
 struct bdi_work {
 	struct list_head list;
-	struct list_head wait_list;
 	struct rcu_head rcu_head;
 
 	unsigned long seen;
@@ -198,7 +197,8 @@ static void bdi_wait_on_work_clear(struct bdi_work *work)
 		    TASK_UNINTERRUPTIBLE);
 }
 
-static struct bdi_work *bdi_alloc_work(struct writeback_control *wbc)
+static void bdi_alloc_queue_work(struct backing_dev_info *bdi,
+				 struct writeback_control *wbc)
 {
 	struct bdi_work *work;
 
@@ -206,7 +206,7 @@ static struct bdi_work *bdi_alloc_work(struct writeback_control *wbc)
 	if (work)
 		bdi_work_init(work, wbc);
 
-	return work;
+	bdi_queue_work(bdi, work);
 }
 
 void bdi_start_writeback(struct writeback_control *wbc)
@@ -216,11 +216,9 @@ void bdi_start_writeback(struct writeback_control *wbc)
 	 * bdi_queue_work() will wake up the thread and flush old data. This
 	 * should ensure some amount of progress in freeing memory.
 	 */
-	if (wbc->sync_mode != WB_SYNC_ALL) {
-		struct bdi_work *w = bdi_alloc_work(wbc);
-
-		bdi_queue_work(wbc->bdi, w);
-	} else {
+	if (wbc->sync_mode != WB_SYNC_ALL)
+		bdi_alloc_queue_work(wbc->bdi, wbc);
+	else {
 		struct bdi_work work;
 
 		bdi_work_init(&work, wbc);
@@ -860,67 +858,26 @@ int bdi_writeback_task(struct bdi_writeback *wb)
 }
 
 /*
- * Schedule writeback for all backing devices. Expensive! If this is a data
- * integrity operation, writeback will be complete when this returns. If
- * we are simply called for WB_SYNC_NONE, then writeback will merely be
- * scheduled to run.
+ * Schedule writeback for all backing devices. Can only be used for
+ * WB_SYNC_NONE writeback, WB_SYNC_ALL should use bdi_start_writeback()
+ * and pass in the superblock.
  */
 static void bdi_writeback_all(struct writeback_control *wbc)
 {
-	const bool must_wait = wbc->sync_mode == WB_SYNC_ALL;
 	struct backing_dev_info *bdi;
-	struct bdi_work *work;
-	LIST_HEAD(list);
 
-restart:
+	WARN_ON(wbc->sync_mode == WB_SYNC_ALL);
+
 	spin_lock(&bdi_lock);
 
 	list_for_each_entry(bdi, &bdi_list, bdi_list) {
-		struct bdi_work *work;
-
 		if (!bdi_has_dirty_io(bdi))
 			continue;
 
-		/*
-		 * If work allocation fails, do the writes inline. We drop
-		 * the lock and restart the list writeout. This should be OK,
-		 * since this happens rarely and because the writeout should
-		 * eventually make more free memory available.
-		 */
-		work = bdi_alloc_work(wbc);
-		if (!work) {
-			struct writeback_control __wbc;
-
-			/*
-			 * Not a data integrity writeout, just continue
-			 */
-			if (!must_wait)
-				continue;
-
-			spin_unlock(&bdi_lock);
-			__wbc = *wbc;
-			__wbc.bdi = bdi;
-			writeback_inodes_wbc(&__wbc);
-			goto restart;
-		}
-		if (must_wait)
-			list_add_tail(&work->wait_list, &list);
-
-		bdi_queue_work(bdi, work);
+		bdi_alloc_queue_work(bdi, wbc);
 	}
 
 	spin_unlock(&bdi_lock);
-
-	/*
-	 * If this is for WB_SYNC_ALL, wait for pending work to complete
-	 * before returning.
-	 */
-	while (!list_empty(&list)) {
-		work = list_entry(list.next, struct bdi_work, wait_list);
-		list_del(&work->wait_list);
-		bdi_wait_on_work_clear(work);
-		call_rcu(&work->rcu_head, bdi_work_free);
-	}
 }
 
 /*
@@ -1177,6 +1134,7 @@ long sync_inodes_sb(struct super_block *sb)
 {
 	struct writeback_control wbc = {
 		.sb		= sb,
+		.bdi		= sb->s_bdi,
 		.sync_mode	= WB_SYNC_ALL,
 		.range_start	= 0,
 		.range_end	= LLONG_MAX,
@@ -1184,7 +1142,7 @@ long sync_inodes_sb(struct super_block *sb)
 	long nr_to_write = LONG_MAX; /* doesn't actually matter */
 
 	wbc.nr_to_write = nr_to_write;
-	bdi_writeback_all(&wbc);
+	bdi_start_writeback(&wbc);
 	wait_sb_inodes(&wbc);
 	return nr_to_write - wbc.nr_to_write;
 }