Re: [PATCH 06/21] RDS: Connection handling

On Tue, Jan 27, 2009 at 02:47:27PM +0100, Oliver Neukum (oliver@neukum.org) wrote:

quoted

quoted

+static inline int rds_conn_is_sending(struct rds_connection *conn)
+{
+	int ret = 0;
+
+	if (!mutex_trylock(&conn->c_send_lock))
+		ret = 1;
+	else
+		mutex_unlock(&conn->c_send_lock);
+
+	return ret;
+}
+

This one is eventually invoked under the spin_lock with turned off irqs,
which may freeze the machine:
rds_for_each_conn_info() -> spin_lock_irqsave(global lock) ->
rds_conn_info_visitor() -> rds_conn_info_set() -> rds_conn_is_sending()
-> boom.

Why? This is _trylock. It won't block.

Unlock may reschedule.

-- 
	Evgeniy Polyakov