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

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Message-Id: <200901271447.29377.oliver@neukum.org>
Date:	Tue, 27 Jan 2009 14:47:27 +0100
From:	Oliver Neukum <oliver@...kum.org>
To:	Evgeniy Polyakov <zbr@...emap.net>
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

Am Tuesday 27 January 2009 14:34:19 schrieb Evgeniy Polyakov:
> On Mon, Jan 26, 2009 at 06:17:43PM -0800, Andy Grover (andy.grover@...cle.com) 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.

	Regards
		Oliver
 


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