[PATCH 2/7] mm/gup: check if both GUP_GET and GUP_PIN are set in __get_user_pages() earlier

[Baoquan He <bhe@redhat.com>]

In __get_user_pages(), it will traverse page table and take a reference
to the page the given user address corresponds to if GUP_GET or GUP_PIN
is et. However, it's not supported both GUP_GET and GUP_PIN are set.
This check should be done earlier, but not doing it till entering into
follow_page_pte() and failed.

Here move the checking to the beginning of __get_user_pages().

Signed-off-by: Baoquan He <bhe@redhat.com>
---
 mm/gup.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 73777b1de679..8788105daee8 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -847,11 +847,6 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
 	pte_t *ptep, pte;
 	int ret;
 
-	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
-	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
-			 (FOLL_PIN | FOLL_GET)))
-		return ERR_PTR(-EINVAL);
-
 	ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
 	if (!ptep)
 		return no_page_table(vma, flags, address);
@@ -1434,6 +1429,11 @@ static long __get_user_pages(struct mm_struct *mm,
 
 	VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
 
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
+			 (FOLL_PIN | FOLL_GET)))
+		return ERR_PTR(-EINVAL);
+
 	do {
 		struct page *page;
 		unsigned int page_increm;
-- 
2.41.0