On Fri, Jul 30, 2021 at 04:25:17PM +0800, Ming Lei wrote:

quoted

+size_t bio_add_folio(struct bio *bio, struct folio *folio, size_t len,
+		size_t off)
+{
+	if (len > UINT_MAX || off > UINT_MAX)
+		return 0;

The added page shouldn't cross 4G boundary, so just wondering why not
check 'if (len > UINT_MAX - off)'?

That check is going to be vulnerable to wrapping, eg
	off = 2^32, len = 512

It would be less vulnerable to wrapping if we cast both sides to
signed long.  But at that point, we're firmly into obscuring the
intent of the check.