net/9p/trans_fd.c: fix race-condition by flushing workqueue before the kfree()

commit 430ac66 upstream.

The patch adds the flush in p9_mux_poll_stop() as it the function used by
p9_conn_destroy(), in turn called by p9_fd_close() to stop the async
polling associated with the data regarding the connection.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Tomas Bortoli <[email protected]>
Reported-by: [email protected]
To: Eric Van Hensbergen <[email protected]>
To: Ron Minnich <[email protected]>
To: Latchesar Ionkov <[email protected]>
Cc: Yiwen Jiang <[email protected]>
Cc: [email protected]
Signed-off-by: Dominique Martinet <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Tomas Bortoli

net/9p/trans_fd.c

@@ -185,6 +185,8 @@ static void p9_mux_poll_stop(struct p9_conn *m)
 	spin_lock_irqsave(&p9_poll_lock, flags);
 	list_del_init(&m->poll_pending_link);
 	spin_unlock_irqrestore(&p9_poll_lock, flags);
+
+	flush_work(&p9_poll_work);
 }
 
 /**