[PATCH] pfnmap: do_no_page BUG_ON again

Use copy_user_highpage directly instead of cow_user_page in do_no_page:
in the immediately following page_cache_release, and elsewhere, it is
assuming that new_page is normal.  If any VM_PFNMAP driver can get to
do_no_page, it's just a BUG (but not in the case of do_anonymous_page).

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/memory.c

@@ -2009,6 +2009,8 @@ static int do_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	int anon = 0;
 
 	pte_unmap(page_table);
+	BUG_ON(vma->vm_flags & VM_PFNMAP);
+
 	if (vma->vm_file) {
 		mapping = vma->vm_file->f_mapping;
 		sequence = mapping->truncate_count;
@@ -2041,7 +2043,7 @@ retry:
 		page = alloc_page_vma(GFP_HIGHUSER, vma, address);
 		if (!page)
 			goto oom;
-		cow_user_page(page, new_page, address);
+		copy_user_highpage(page, new_page, address);
 		page_cache_release(new_page);
 		new_page = page;
 		anon = 1;