On 2011-09-18 16:02, Philippe Gerum wrote:
> On Fri, 2011-09-16 at 22:39 +0200, Gilles Chanteperdrix wrote:
>> On 09/16/2011 10:13 PM, Gilles Chanteperdrix wrote:
>>> On 09/11/2011 04:29 PM, Jan Kiszka wrote:
>>>> On 2011-09-11 16:24, Gilles Chanteperdrix wrote:
>>>>> On 09/11/2011 12:50 PM, Jan Kiszka wrote:
>>>>>> Hi all,
>>>>>>
>>>>>> just looked into the hrescnt issue again, specifically the corner case
>>>>>> of a shadow thread switching from real-time policy to SCHED_OTHER.
>>>>>
>>>>> Doing this while holding a mutex looks invalid.
>>>>
>>>> Looking at POSIX e.g., is there anything in the spec that makes this
>>>> invalid? If the kernel preserves or established proper priority
>>>> boosting, I do not see what could break in principle.
>>>>
>>>> It is nothing I would design into some app, but we should somehow handle
>>>> it (doc update or code adjustments).
>>>>
>>>>> If we do not do it, the current code is valid.
>>>>
>>>> Except for its dependency on XNOTHER which is not updated on RT->NORMAL
>>>> transitions.
>>>
>>> The fact that this update did not take place made the code work. No 
>>> negative rescnt could happen with that code.
>>>
>>> Anyway, here is a patch to allow switching back from RT to NORMAL, but 
>>> send a SIGDEBUG to a thread attempting to release a mutex while its 
>>> counter is already 0. We end up avoiding a big chunk of code that would 
>>> have been useful for a really strange corner case.
>>>
>>
>> Here comes version 2:
>> diff --git a/include/nucleus/sched-idle.h b/include/nucleus/sched-idle.h
>> index 6399a17..417170f 100644
>> --- a/include/nucleus/sched-idle.h
>> +++ b/include/nucleus/sched-idle.h
>> @@ -39,6 +39,8 @@ extern struct xnsched_class xnsched_class_idle;
>>  static inline void __xnsched_idle_setparam(struct xnthread *thread,
>>                                         const union xnsched_policy_param *p)
>>  {
>> +    if (xnthread_test_state(thread, XNSHADOW))
>> +            xnthread_clear_state(thread, XNOTHER);
>>      thread->cprio = p->idle.prio;
>>  }
>>  
>> diff --git a/include/nucleus/sched-rt.h b/include/nucleus/sched-rt.h
>> index 71f655c..cc1cefa 100644
>> --- a/include/nucleus/sched-rt.h
>> +++ b/include/nucleus/sched-rt.h
>> @@ -86,6 +86,12 @@ static inline void __xnsched_rt_setparam(struct xnthread 
>> *thread,
>>                                       const union xnsched_policy_param *p)
>>  {
>>      thread->cprio = p->rt.prio;
>> +    if (xnthread_test_state(thread, XNSHADOW)) {
>> +            if (thread->cprio)
>> +                    xnthread_clear_state(thread, XNOTHER);
>> +            else
>> +                    xnthread_set_state(thread, XNOTHER);
>> +    }
>>  }
>>  
>>  static inline void __xnsched_rt_getparam(struct xnthread *thread,
>> diff --git a/ksrc/nucleus/pod.c b/ksrc/nucleus/pod.c
>> index 9a02e80..d19999f 100644
>> --- a/ksrc/nucleus/pod.c
>> +++ b/ksrc/nucleus/pod.c
>> @@ -1896,16 +1896,6 @@ int __xnpod_set_thread_schedparam(struct xnthread 
>> *thread,
>>              xnsched_putback(thread);
>>  
>>  #ifdef CONFIG_XENO_OPT_PERVASIVE
>> -    /*
>> -     * A non-real-time shadow may upgrade to real-time FIFO
>> -     * scheduling, but the latter may never downgrade to
>> -     * SCHED_NORMAL Xenomai-wise. In the valid case, we clear
>> -     * XNOTHER to reflect the change. Note that we keep handling
>> -     * non real-time shadow specifics in higher code layers, not
>> -     * to pollute the core scheduler with peculiarities.
>> -     */
>> -    if (sched_class == &xnsched_class_rt && sched_param->rt.prio > 0)
>> -            xnthread_clear_state(thread, XNOTHER);
>>      if (propagate) {
>>              if (xnthread_test_state(thread, XNRELAX))
>>                      xnshadow_renice(thread);
>> diff --git a/ksrc/nucleus/sched-sporadic.c b/ksrc/nucleus/sched-sporadic.c
>> index fd37c21..ffc9bab 100644
>> --- a/ksrc/nucleus/sched-sporadic.c
>> +++ b/ksrc/nucleus/sched-sporadic.c
>> @@ -258,6 +258,8 @@ static void xnsched_sporadic_setparam(struct xnthread 
>> *thread,
>>              }
>>      }
>>  
>> +    if (xnthread_test_state(thread, XNSHADOW))
>> +            xnthread_clear_state(thread, XNOTHER);
>>      thread->cprio = p->pss.current_prio;
>>  }
>>  
>> diff --git a/ksrc/nucleus/sched-tp.c b/ksrc/nucleus/sched-tp.c
>> index 43a548e..a2af1d3 100644
>> --- a/ksrc/nucleus/sched-tp.c
>> +++ b/ksrc/nucleus/sched-tp.c
>> @@ -100,6 +100,8 @@ static void xnsched_tp_setparam(struct xnthread *thread,
>>  {
>>      struct xnsched *sched = thread->sched;
>>  
>> +    if (xnthread_test_state(thread, XNSHADOW))
>> +            xnthread_clear_state(thread, XNOTHER);
>>      thread->tps = &sched->tp.partitions[p->tp.ptid];
>>      thread->cprio = p->tp.prio;
>>  }
>> diff --git a/ksrc/nucleus/synch.c b/ksrc/nucleus/synch.c
>> index b956e46..47bc0c5 100644
>> --- a/ksrc/nucleus/synch.c
>> +++ b/ksrc/nucleus/synch.c
>> @@ -684,9 +684,13 @@ xnsynch_release_thread(struct xnsynch *synch, struct 
>> xnthread *lastowner)
>>  
>>      XENO_BUGON(NUCLEUS, !testbits(synch->status, XNSYNCH_OWNER));
>>  
>> -    if (xnthread_test_state(lastowner, XNOTHER))
>> -            xnthread_dec_rescnt(lastowner);
>> -    XENO_BUGON(NUCLEUS, xnthread_get_rescnt(lastowner) < 0);
>> +    if (xnthread_test_state(lastowner, XNOTHER)) {
>> +            if (xnthread_get_rescnt(lastowner) == 0)
>> +                    xnshadow_send_sig(lastowner, SIGDEBUG,
>> +                                      SIGDEBUG_MIGRATE_PRIOINV, 1);
>> +            else
>> +                    xnthread_dec_rescnt(lastowner);
>> +    }
>>      lastownerh = xnthread_handle(lastowner);
>>  
>>      if (use_fastlock &&
>>
>>
>>
> 
> Agreed, the logic of this patch sounds right. Switching from -rt to -nrt
> while holding a -rt mutex is pathological behavior. We don't have to
> support apps implementing voluntary priority inversion.
> 

No concerns either.

Now we just need

diff --git a/ksrc/nucleus/shadow.c b/ksrc/nucleus/shadow.c
index 21cc191..27bc829 100644
--- a/ksrc/nucleus/shadow.c
+++ b/ksrc/nucleus/shadow.c
@@ -2756,9 +2756,12 @@ static inline void do_setsched_event(struct task_struct 
*p, int priority)
        union xnsched_policy_param param;
        struct xnsched *sched;
 
-       if (!thread || p->policy != SCHED_FIFO)
+       if (!thread)
                return;
 
+       if (p->policy == SCHED_FIFO)
+               priority = 0;
+
        /*
         * Linux's priority scale is a subset of the core pod's
         * priority scale, so there is no need to bound the priority


to track the policy change when done via Linux.

Jan

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