Jan Kiszka wrote:
> Am 04.11.2010 00:11, Gilles Chanteperdrix wrote:
>> Jan Kiszka wrote:
>>> Am 03.11.2010 23:11, Jan Kiszka wrote:
>>>> Am 03.11.2010 23:03, Jan Kiszka wrote:
>>>>> But we not not always use atomic ops for manipulating status bits (but
>>>>> we do in other cases where this is no need - different story). This may
>>>>> fix the race:
>>>> Err, nonsense. As we manipulate xnsched::status also outside of nklock
>>>> protection, we must _always_ use atomic ops.
>>>>
>>>> This screams for a cleanup: local-only bits like XNHTICK or XNINIRQ
>>>> should be pushed in a separate status word that can then be safely
>>>> modified non-atomically.
>>> Second try to fix and clean up the sched status bits. Anders, please
>>> test.
>>>
>>> Jan
>>>
>>> diff --git a/include/nucleus/pod.h b/include/nucleus/pod.h
>>> index 01ff0a7..5987a1f 100644
>>> --- a/include/nucleus/pod.h
>>> +++ b/include/nucleus/pod.h
>>> @@ -277,12 +277,10 @@ static inline void xnpod_schedule(void)
>>>      * context is active, or if we are caught in the middle of a
>>>      * unlocked context switch.
>>>      */
>>> -#if XENO_DEBUG(NUCLEUS)
>>>     if (testbits(sched->status, XNKCOUT|XNINIRQ|XNSWLOCK))
>>>             return;
>>> -#else /* !XENO_DEBUG(NUCLEUS) */
>>> -   if (testbits(sched->status,
>>> -                XNKCOUT|XNINIRQ|XNSWLOCK|XNRESCHED) != XNRESCHED)
>>> +#if !XENO_DEBUG(NUCLEUS)
>>> +   if (!sched->resched)
>>>             return;
>>>  #endif /* !XENO_DEBUG(NUCLEUS) */
>> Having only one test was really nice here, maybe we simply read a
>> barrier before reading the status?
>>
> 
> I agree - but the alternative is letting all modifications of
> xnsched::status use atomic bitops (that's required when folding all bits
> into a single word). And that should be much more costly, specifically
> on SMP.

What about issuing a barrier before testing the status?

-- 
                                                                Gilles.

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