On Tue, 5 May 2015, Steven Rostedt wrote:
> On Tue, 5 May 2015 18:31:20 +0200 (CEST)
> Thomas Gleixner <t...@linutronix.de> wrote:
>
> > On Tue, 5 May 2015, Steven Rostedt wrote:
> > > I got pulled onto other things so I never finished it, but one thing
> > > that worried me about this fix is this:
> > >
> > > T1 - FIFO policy (prio = 10)
> > > lock(rtmutex);
> > >
> > > T2 (prio = 20)
> > > lock(rtmutex)
> > > boost T1 (prio = 20)
> > >
> > > TI (prio = 20)
> > > sys_sched_setscheduler(prio = 30)
> > > TI (prio = 30)
> > >
> > > T1 (prio = 30)
> > > sys_sched_setscheduler(SCHED_OTHER)
> > > new_effective_prio = 20, oldprio = 30
> > >
> > > Before the code stopped at the rt_mutex_check_prio(), but now it
> > > continues. Will having the policy change cause problems here?
> >
> > No, because it stays effective in the FIFO domain.
> >
>
> Ah, the policy passed in isn't used, so we are safe. But, but I also
> found that we still call __setscheduler(), which does:
>
> p->prio = normal_prio();
>
> Isn't that going to null out the boosting?
Crap. Yes, I missed that. So __setscheduler() assumes that there is no
boosting going on. So we need:
p->prio = effective_prio(p);
there instead.
Thanks,
tglx
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