the check_stack_guard_page() has, under certain circumstances, side-effects which can not easily be undone in case the vx_rss_avail() fails

diff --git a/mm/memory.c b/mm/memory.c
index c53939d..158c500 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2439,13 +2439,14 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
 
 	pte_unmap(page_table);
 
+	if (!vx_rss_avail(mm, 1))
+		goto oom;
+
 	/* Check if we need to add a guard page to the stack */
 	if (check_stack_guard_page(vma, address) < 0)
 		return VM_FAULT_SIGBUS;
 
 	/* Allocate our own private page. */
-	if (!vx_rss_avail(mm, 1))
-		goto oom;
 	if (unlikely(anon_vma_prepare(vma)))
 		goto oom;
 	page = alloc_zeroed_user_highpage_movable(vma, address);