On Tue, 9 Oct 2018 17:42:09 -0700 John Hubbard <jhubbard@xxxxxxxxxx> wrote: > > Also, maintainability. What happens if someone now uses put_page() by > > mistake? Kernel fails in some mysterious fashion? How can we prevent > > this from occurring as code evolves? Is there a cheap way of detecting > > this bug at runtime? > > > > It might be possible to do a few run-time checks, such as "does page that came > back to put_user_page() have the correct flags?", but it's harder (without > having a dedicated page flag) to detect the other direction: "did someone page > in a get_user_pages page, to put_page?" > > As Jan said in his reply, converting get_user_pages (and put_user_page) to > work with a new data type that wraps struct pages, would solve it, but that's > an awfully large change. Still...given how much of a mess this can turn into > if it's wrong, I wonder if it's worth it--maybe? This is a real worry. If someone uses a mistaken put_page() then how will that bug manifest at runtime? Under what set of circumstances will the kernel trigger the bug? (btw, please cc me on all patches, not just [0/n]!)
