fuse: notify: don't move pages

commit 0d278362 upstream.

fuse_try_move_page() is not prepared for replacing pages that have already
been read.
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

fs/fuse/dev.c

@@ -1721,6 +1721,9 @@ static int fuse_notify_retrieve(struct fuse_conn *fc, unsigned int size,
 static int fuse_notify(struct fuse_conn *fc, enum fuse_notify_code code,
 		       unsigned int size, struct fuse_copy_state *cs)
 {
+	/* Don't try to move pages (yet) */
+	cs->move_pages = 0;
+
 	switch (code) {
 	case FUSE_NOTIFY_POLL:
 		return fuse_notify_poll(fc, size, cs);