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

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Date:	Tue, 27 Jan 2009 16:51:44 +0300
From:	Evgeniy Polyakov <zbr@...emap.net>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	Andy Grover <andy.grover@...cle.com>, rdreier@...co.com,
	rds-devel@....oracle.com, general@...ts.openfabrics.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH 06/21] RDS: Connection handling

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