[PATCH v2] mm/gup.c: Fix return value for __gup_longterm_locked()

[Shigeru Yoshida]

__get_user_pages_locked() may return the number of pages less than
nr_pages.  So __gup_longterm_locked() have to return the number of
pages __get_user_pages_locked() returns if it succeeded, not nr_pages
requested.

Fixes: 61c63c2076d9 (mm/gup.c: simplify and fix check_and_migrate_movable_pages() return codes)
CC: Alistair Popple <apopple@xxxxxxxxxx>
Reported-by: syzbot+616ff0452fec30f4dcfd@xxxxxxxxxxxxxxxxxxxxxxxxx
Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
Signed-off-by: Shigeru Yoshida <syoshida@xxxxxxxxxx>
---
 mm/gup.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 5aa7531a703b..66582203220a 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2068,22 +2068,24 @@ static long __gup_longterm_locked(struct mm_struct *mm,
 				  unsigned int gup_flags)
 {
 	unsigned int flags;
-	long rc;
+	long rc, nr_pinned_pages;
 
 	if (!(gup_flags & FOLL_LONGTERM))
 		return __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
 					       NULL, gup_flags);
 	flags = memalloc_pin_save();
 	do {
-		rc = __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
-					     NULL, gup_flags);
-		if (rc <= 0)
+		nr_pinned_pages =
+			__get_user_pages_locked(mm, start, nr_pages, pages,
+						vmas, NULL, gup_flags);
+		if (nr_pinned_pages <= 0)
 			break;
-		rc = check_and_migrate_movable_pages(rc, pages, gup_flags);
+		rc = check_and_migrate_movable_pages(nr_pinned_pages, pages,
+						     gup_flags);
 	} while (rc == -EAGAIN);
 	memalloc_pin_restore(flags);
 
-	return rc ? rc : nr_pages;
+	return rc ? rc : nr_pinned_pages;
 }
 
 static bool is_valid_gup_flags(unsigned int gup_flags)
-- 
2.37.2