On Fri, Aug 06, 2021 at 04:12:35PM +0800, Qu Wenruo wrote:

+					    pgoff_t index)
+{
+	struct address_space *mapping = inode->vfs_inode.i_mapping;
+	gfp_t mask = btrfs_alloc_write_mask(mapping);
+	u64 page_start = index << PAGE_SHIFT;

This needs (u64)index << PAGE_SHIFT, the types are not 64bit safe.

+	u64 page_end = page_start + PAGE_SIZE - 1;
+	struct extent_state *cached_state = NULL;
+	struct page *page;
+	int ret;
+
+again:
+	page = find_or_create_page(mapping, index, mask);
+	if (!page)
+		return ERR_PTR(-ENOMEM);
+
+	ret = set_page_extent_mapped(page);
+	if (ret < 0) {
+		unlock_page(page);
+		put_page(page);
+		return ERR_PTR(ret);
+	}
+
+	/* Wait for any exists ordered extent in the range */

                        existing

+	while (1) {
+		struct btrfs_ordered_extent *ordered;
+
+		lock_extent_bits(&inode->io_tree, page_start, page_end,
+				 &cached_state);
+		ordered = btrfs_lookup_ordered_range(inode, page_start,
+						     PAGE_SIZE);
+		unlock_extent_cached(&inode->io_tree, page_start, page_end,
+				     &cached_state);
+		if (!ordered)
+			break;
+
+		unlock_page(page);
+		btrfs_start_ordered_extent(ordered, 1);
+		btrfs_put_ordered_extent(ordered);
+		lock_page(page);
+		/*
+		 * we unlocked the page above, so we need check if
+		 * it was released or not.
+		 */

Please reformat comments that are moved

+		if (page->mapping != mapping || !PagePrivate(page)) {
+			unlock_page(page);
+			put_page(page);
+			goto again;
+		}
+	}
+
+	/*
+	 * Now the page range has no ordered extent any more.
+	 * Read the page to make it uptodate.

Same.

+	 */
+	if (!PageUptodate(page)) {
+		btrfs_readpage(NULL, page);
+		lock_page(page);
+		if (page->mapping != mapping || !PagePrivate(page)) {
+			unlock_page(page);
+			put_page(page);
+			goto again;
+		}
+		if (!PageUptodate(page)) {
+			unlock_page(page);
+			put_page(page);
+			return ERR_PTR(-EIO);
+		}
+	}
+	return page;
+}