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

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.

Fix both cases by catching the page==NULL cases with no_page_table().

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
Fixes: 080dbb618b4b ("mm/follow_page_mask: split follow_page_mask to smaller functions.")
Signed-off-by: Peter Xu <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Aneesh Kumar K.V <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions