On 09/18/2011 05:13 PM, Jan Kiszka wrote:
> On 2011-09-18 17:11, Jan Kiszka wrote:
>> On 2011-09-18 17:10, Philippe Gerum wrote:
>>> On Sun, 2011-09-18 at 16:34 +0200, Jan Kiszka wrote:
>>>> 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)
>>> ^^
>>> inverted?
>>
>> Of course.
>
> Thinking about SCHED_RR or other policies, this still looks fishy and
> needs some thoughts.
What about:
diff --git a/ksrc/nucleus/shadow.c b/ksrc/nucleus/shadow.c
index 21cc191..7fe44a1 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 || (p->policy != SCHED_FIFO && p->policy != SCHED_OTHER))
return;
+ if (p->policy == SCHED_OTHER)
+ 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
--
Gilles.
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