Re: [PATCH] mm/gup: Fix follow_devmap_p[mu]d() on page==NULL handling

[Andrew Morton]

On Thu, 23 Nov 2023 13:02:22 -0500 Peter Xu <peterx@xxxxxxxxxx> wrote:

> This is a bug found not by any report but only by code observations.
> 
> When GUP sees a devpmd/devpud and if page==NULL is returned, it means a
> fault is probably required.  Here falling through when page==NULL can cause
> unexpected behavior.
> 

Well this is worrisome.  We aren't able to construct a test case to
demonstrate this bug?  Why is that?  Is it perhaps just dead code?