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SubjectRe: [PATCH v4 2/3] mm: introduce put_user_page*(), placeholder versions
On Tue, 9 Oct 2018 10:30:25 +0200 Jan Kara <jack@suse.cz> 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?
>
> The same will happen as with any other reference counting bug - the special
> user reference will leak. It will be pretty hard to debug I agree. I was
> thinking about whether we could provide some type safety against such bugs
> such as get_user_pages() not returning struct page pointers but rather some
> other special type but it would result in a big amount of additional churn
> as we'd have to propagate this different type e.g. through the IO path so
> that IO completion routines could properly call put_user_pages(). So I'm
> not sure it's really worth it.

I'm not really understanding. Patch 3/3 changes just one infiniband
driver to use put_user_page(). But the changelogs here imply (to me)
that every user of get_user_pages() needs to be converted to
s/put_page/put_user_page/.

Methinks a bit more explanation is needed in these changelogs?

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