There really should be no circumstances under which a non-FOLL_NOWAIT GUP operation fails to return any pages, so make this an error and warn on it. To catch the trivial case, simply exit early if nr_pages == 0. This brings __get_user_pages_locked() in line with the behaviour of its nommu variant. Reviewed-by: Arnd Bergmann <arnd@xxxxxxxx> Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx> --- mm/gup.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/mm/gup.c b/mm/gup.c index b21b33d1787e..231711efa390 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1471,6 +1471,9 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm, long ret, pages_done; bool must_unlock = false; + if (!nr_pages) + return 0; + /* * The internal caller expects GUP to manage the lock internally and the * lock must be released when this returns. @@ -1595,6 +1598,14 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm, mmap_read_unlock(mm); *locked = 0; } + + /* + * Failing to pin anything implies something has gone wrong (except when + * FOLL_NOWAIT is specified). + */ + if (WARN_ON_ONCE(pages_done == 0 && !(flags & FOLL_NOWAIT))) + return -EFAULT; + return pages_done; } -- 2.42.0
