1 files changed, 15 insertions, 1 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 691f2264a6ce..0b7656e804d1 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -696,8 +696,22 @@ static void prep_compound_gigantic_page(struct page *page, unsigned long order)
         /* we rely on prep_new_huge_page to set the destructor */
         set_compound_order(page, order);
         __SetPageHead(page);
+        __ClearPageReserved(page);
         for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
                 __SetPageTail(p);
+                /*
+                 * For gigantic hugepages allocated through bootmem at
+                 * boot, it's safer to be consistent with the not-gigantic
+                 * hugepages and clear the PG_reserved bit from all tail pages
+                 * too.  Otherwse drivers using get_user_pages() to access tail
+                 * pages may get the reference counting wrong if they see
+                 * PG_reserved set on a tail page (despite the head page not
+                 * having PG_reserved set).  Enforcing this consistency between
+                 * head and tail pages allows drivers to optimize away a check
+                 * on the head page when they need know if put_page() is needed
+                 * after get_user_pages().
+                 */
+                __ClearPageReserved(p);
                 set_page_count(p, 0);
                 p->first_page = page;
         }
@@ -1330,9 +1344,9 @@ static void __init gather_bootmem_prealloc(void)
 #else
                 page = virt_to_page(m);
 #endif
-                __ClearPageReserved(page);
                 WARN_ON(page_count(page) != 1);
                 prep_compound_huge_page(page, h->order);
+                WARN_ON(PageReserved(page));
                 prep_new_huge_page(h, page, page_to_nid(page));
                 /*
                  * If we had gigantic hugepages allocated at boot time, we need