[ofa-general] Re: [PATCH 06/21] RDS: Connection handling
Steve Wise
swise at opengridcomputing.com
Tue Jan 27 08:28:48 PST 2009
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 at oracle.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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