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

From: Steve Wise <[email-masked]>
Date: Tue, 27 Jan 2009 10:28:48 -0600

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 ([email-masked]) 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());