Re: [Xenomai-core] Potential problem with rt_eepro100

[Philippe Gerum <rpm@xenomai.org>]

On Wed, 2010-11-03 at 20:38 +0100, Anders Blomdell wrote:
> Jan Kiszka wrote:
> > Am 03.11.2010 17:46, Anders Blomdell wrote:
> >> Anders Blomdell wrote:
> >>> Anders Blomdell wrote:
> >>>> Jan Kiszka wrote:
> >>>>> additional barrier. Can you check this?
> >>>>>
> >>>>> diff --git a/include/nucleus/sched.h b/include/nucleus/sched.h
> >>>>> index df56417..66b52ad 100644
> >>>>> --- a/include/nucleus/sched.h
> >>>>> +++ b/include/nucleus/sched.h
> >>>>> @@ -187,6 +187,7 @@ static inline int xnsched_self_resched_p(struct 
> >>>>> xnsched *sched)
> >>>>>    if (current_sched != (__sched__))    {                \
> >>>>>        xnarch_cpu_set(xnsched_cpu(__sched__), 
> >>>>> current_sched->resched);    \
> >>>>>        setbits((__sched__)->status, XNRESCHED);                \
> >>>>> +      xnarch_memory_barrier();                        \
> >>>>>    }                                    \
> >>>>>  } while (0)
> >>>> In progress, if nothing breaks before, I'll report status tomorrow 
> >>>> morning.
> >>> It still breaks (in approximately the same way). I'm currently putting a 
> >>> barrier in the other macro doing a RESCHED, also adding some tracing to 
> >>> see if a read barrier is needed.
> >> Nope, no luck there either. Will start interesting tracepoint 
> >> adding/conversion :-(
> > 
> > Strange. But it was too easy anyway...
> > 
> >> Any reason why xn_nucleus_sched_remote should ever report status = 0?
> > 
> > Really don't know yet. You could trigger on this state and call
> > ftrace_stop() then. Provided you had the functions tracer enabled, that
> > should give a nice pictures of what happened before.
> 
> Isn't there a race betweeen these two (still waiting for compilation to 
> be finished)?

We always hold the nklock in both contexts.

> 
> static inline int __xnpod_test_resched(struct xnsched *sched)
> {
> 	int resched = testbits(sched->status, XNRESCHED);
> #ifdef CONFIG_SMP
> 	/* Send resched IPI to remote CPU(s). */
> 	if (unlikely(xnsched_resched_p(sched))) {
> 		xnarch_send_ipi(sched->resched);
> 		xnarch_cpus_clear(sched->resched);
> 	}
> #endif
> 	clrbits(sched->status, XNRESCHED);
> 	return resched;
> }
> 
> #define xnsched_set_resched(__sched__) do {                   \
>    xnsched_t *current_sched = xnpod_current_sched();           \
>    setbits(current_sched->status, XNRESCHED);                  \
>    if (current_sched != (__sched__))     {                     \
>        xnarch_cpu_set(xnsched_cpu(__sched__), current_sched->resched); \
>        setbits((__sched__)->status, XNRESCHED);                \
>        xnarch_memory_barrier();                                \
>    }                                                           \
> } while (0)
> 
> I would suggest (if I have got all the macros right):
> 
> static inline int __xnpod_test_resched(struct xnsched *sched)
> {
> 	int resched = testbits(sched->status, XNRESCHED);
> 	if (unlikely(resched)) {
> #ifdef CONFIG_SMP
> 		/* Send resched IPI to remote CPU(s). */
> 		xnarch_send_ipi(sched->resched);
> 		xnarch_cpus_clear(sched->resched);
> #endif
> 		clrbits(sched->status, XNRESCHED);
> 	}
> 	return resched;
> }
> 
> /Anders
> 
> 
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-- 
Philippe.