btrfs: Always use a cached extent_state in btrfs_lock_and_flush_ordered_range

In case no cached_state argument is passed to
btrfs_lock_and_flush_ordered_range use one locally in the function. This
optimises the case when an ordered extent is found since the unlock
function will be able to unlock that state directly without searching
for it again.
Reviewed-by: NJosef Bacik <josef@toxicpanda.com>
Signed-off-by: NNikolay Borisov <nborisov@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/ordered-data.c

@@ -982,14 +982,26 @@ void btrfs_lock_and_flush_ordered_range(struct extent_io_tree *tree,
 					struct extent_state **cached_state)
 {
 	struct btrfs_ordered_extent *ordered;
+	struct extent_state *cachedp = NULL;
+
+	if (cached_state)
+		cachedp = *cached_state;
 
 	while (1) {
-		lock_extent_bits(tree, start, end, cached_state);
+		lock_extent_bits(tree, start, end, &cachedp);
 		ordered = btrfs_lookup_ordered_range(inode, start,
 						     end - start + 1);
-		if (!ordered)
+		if (!ordered) {
+			/*
+			 * If no external cached_state has been passed then
+			 * decrement the extra ref taken for cachedp since we
+			 * aren't exposing it outside of this function
+			 */
+			if (!cached_state)
+				refcount_dec(&cachedp->refs);
 			break;
-		unlock_extent_cached(tree, start, end, cached_state);
+		}
+		unlock_extent_cached(tree, start, end, &cachedp);
 		btrfs_start_ordered_extent(&inode->vfs_inode, ordered, 1);
 		btrfs_put_ordered_extent(ordered);
 	}