mm/hugetlb: prepare hugetlb_follow_page_mask() for FOLL_PIN

follow_page() doesn't use FOLL_PIN, meanwhile hugetlb seems to not be the
target of FOLL_WRITE either.  However add the checks.

Namely, either the need to CoW due to missing write bit, or proper
unsharing on !AnonExclusive pages over R/O pins to reject the follow page.
That brings this function closer to follow_hugetlb_page().

So we don't care before, and also for now.  But we'll care if we switch
over slow-gup to use hugetlb_follow_page_mask().  We'll also care when to
return -EMLINK properly, as that's the gup internal api to mean "we should
unshare".  Not really needed for follow page path, though.

When at it, switching the try_grab_page() to use WARN_ON_ONCE(), to be
clear that it just should never fail.  When error happens, instead of
setting page==NULL, capture the errno instead.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Peter Xu <[email protected]>
Reviewed-by: Mike Kravetz <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: James Houghton <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Kirill A . Shutemov <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Mike Rapoport (IBM) <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Yang Shi <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions