Oliver Neukum wrote:

Am Tuesday 27 January 2009 14:34:19 schrieb Evgeniy Polyakov:
  

quoted

On Mon, Jan 26, 2009 at 06:17:43PM -0800, Andy Grover (andy.grover@oracle.com) wrote:
    

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.

  

mutex_trylock() uses spin_lock_mutex() which has this in the debug version:

DEBUG_LOCKS_WARN_ON(in_interrupt());