nfs_write_end(): fix handling of short copies

commit c0cf3ef5 upstream.

What matters when deciding if we should make a page uptodate is
not how much we _wanted_ to copy, but how much we actually have
copied.  As it is, on architectures that do not zero tail on
short copy we can leave uninitialized data in page marked uptodate.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

fs/nfs/file.c

@@ -403,7 +403,7 @@ static int nfs_write_end(struct file *file, struct address_space *mapping,
 	 */
 	if (!PageUptodate(page)) {
 		unsigned pglen = nfs_page_length(page);
-		unsigned end = offset + len;
+		unsigned end = offset + copied;
 
 		if (pglen == 0) {
 			zero_user_segments(page, 0, offset,