fuse: notify: don't move pages

commit 0d2783626a53d4c922f82d51fa675cb5d13f0d36 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: Zefan Li <lizefan@huawei.com>
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 1f81f70..f26d693 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1638,6 +1638,9 @@
 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);