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

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Date:	Tue, 27 Jan 2009 10:28:48 -0600
From:	Steve Wise <swise@...ngridcomputing.com>
To:	Oliver Neukum <oliver@...kum.org>
CC:	Evgeniy Polyakov <zbr@...emap.net>, netdev@...r.kernel.org,
	rdreier@...co.com, rds-devel@....oracle.com,
	general@...ts.openfabrics.org
Subject: Re: [ofa-general] Re: [PATCH 06/21] RDS: Connection handling

Oliver Neukum wrote:
> 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.
>
>   
mutex_trylock() uses spin_lock_mutex() which has this in the debug version:

DEBUG_LOCKS_WARN_ON(in_interrupt());

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