On 10/10/2012 10:10 AM, Jan Kiszka wrote:
> On 2012-10-10 10:04, Gilles Chanteperdrix wrote:
>> On 10/10/2012 09:56 AM, Jan Kiszka wrote:
>>> On 2012-10-10 09:51, Gilles Chanteperdrix wrote:
>>>> On 10/10/2012 09:38 AM, Thierry Bultel wrote:
>>>>> Hi Gilles,
>>>>>
>>>>> Many thanks,
>>>>> The first patch does not work, the second does.
>>>>> I think the reason for 1st patch why is that in rtcan_virt, we have
>>>>>
>>>>> rtdm_lock_get_irqsave(&rtcan_recv_list_lock, lock_ctx);
>>>>> rtdm_lock_get(&rtcan_socket_lock);
>>>>>
>>>>> ...
>>>>> ---> rtcan_rcv(rx_dev, &skb);
>>>>> ....
>>>>>
>>>>> rtdm_lock_put(&rtcan_socket_lock);
>>>>> rtdm_lock_put_irqrestore(&rtcan_recv_list_lock, lock_ctx);
>>>>>
>>>>> and rtcan_rcv->rtcan_rcv_deliver->rtdm_sem_up(&sock->recv_sem);
>>>>>
>>>>> thus the same re-scheduling stuff with interrupts locked.
>>>>>
>>>>> Are you not not afraid of side effects with the second patch,
>>>>> since you change the overall behaviour ?
>>>>> Won't you prefer a only locally modified rtcan_virt ?
>>>>
>>>> We should ask Jan's opinion. In any case, if we adopt the second patch,
>>>> we might want to try and reduce the overhead of xnpod_unlock_sched.
>>>>
>>>
>>> We were signaling the semaphore while holding a spin lock? That's a
>>> clear bug. Your patch is aligning rtcan to the pattern we are also using
>>> in RTnet. We just need to make sure (haven't looked at the full context
>>> yet) that sock remains valid even after dropping the lock(s).
>>
>> The second patch idea was to lock the scheduler while spinlocks are
>> held, so that posting a semaphore while holding a spin lock is no longer
>> a bug.
>
> Sounds a bit hacky,
Well, that is what the linux kernel does.
but I think we have this pattern
> (RTDM_EXECUTE_ATOMICALLY)
RTDM_EXECUTE_ATOMICALLY is a bit of a misnomer, if you do:
RTDM_EXECUTE_ATOMICALLY(foo(); rtdm_sem_up(); bar());
foo() and bar() are not executed atomically if sem_up wakes up another
thread.
So, I do not see how RTDM_EXECUTE_ATOMICALLY solves the issue we are
talking about.
--
Gilles.
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