Btrfs: extent_write_locked_range() should attach inode->i_wb

extent_write_locked_range() is used when we're falling back to buffered
IO from inside of compression.  It allocates its own wbc and should
associate it with the inode's i_wb to make sure the IO goes down from
the correct cgroup.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Chris Mason <clm@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -4255,6 +4255,7 @@ int extent_write_locked_range(struct inode *inode, u64 start, u64 end,
 		.no_cgroup_owner = 1,
 	};
 
+	wbc_attach_fdatawrite_inode(&wbc_writepages, inode);
 	while (start <= end) {
 		page = find_get_page(mapping, start >> PAGE_SHIFT);
 		if (clear_page_dirty_for_io(page))
@@ -4269,11 +4270,12 @@ int extent_write_locked_range(struct inode *inode, u64 start, u64 end,
 	}
 
 	ASSERT(ret <= 0);
-	if (ret < 0) {
+	if (ret == 0)
+		ret = flush_write_bio(&epd);
+	else
 		end_write_bio(&epd, ret);
-		return ret;
-	}
-	ret = flush_write_bio(&epd);
+
+	wbc_detach_inode(&wbc_writepages);
 	return ret;
 }