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?
> + 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
>
--
Philippe.
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