PM: hibernate: Use __get_safe_page() rather than touching the list

We found at least one situation where the safe pages list was empty and
get_buffer() would gladly try to use a NULL pointer.

Signed-off-by: Brian Geffon <bgeffon@google.com>
Fixes: 8357376 ("[PATCH] swsusp: Improve handling of highmem")
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: bgaff

kernel/power/snapshot.c

@@ -2545,8 +2545,9 @@ static void *get_highmem_page_buffer(struct page *page,
 		pbe->copy_page = tmp;
 	} else {
 		/* Copy of the page will be stored in normal memory */
-		kaddr = safe_pages_list;
-		safe_pages_list = safe_pages_list->next;
+		kaddr = __get_safe_page(ca->gfp_mask);
+		if (!kaddr)
+			return ERR_PTR(-ENOMEM);
 		pbe->copy_page = virt_to_page(kaddr);
 	}
 	pbe->next = highmem_pblist;
@@ -2750,8 +2751,9 @@ static void *get_buffer(struct memory_bitmap *bm, struct chain_allocator *ca)
 		return ERR_PTR(-ENOMEM);
 	}
 	pbe->orig_address = page_address(page);
-	pbe->address = safe_pages_list;
-	safe_pages_list = safe_pages_list->next;
+	pbe->address = __get_safe_page(ca->gfp_mask);
+	if (!pbe->address)
+		return ERR_PTR(-ENOMEM);
 	pbe->next = restore_pblist;
 	restore_pblist = pbe;
 	return pbe->address;