mm/gup: fix comments to pin_user_pages_*()

pin_user_pages API forces FOLL_PIN in gup_flags, which means that the API
requires struct page **pages to be provided (not NULL).  However, the
comment to pin_user_pages() clearly allows for passing in a NULL @pages
argument.

Remove the incorrect comments, and add WARN_ON_ONCE(!pages) calls to
enforce the API.

It has been independently spotted by Minchan Kim and confirmed with
John Hubbard:

https://lore.kernel.org/all/[email protected]/

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Yury Norov (NVIDIA) <[email protected]>
Reviewed-by: John Hubbard <[email protected]>
Cc: Minchan Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions