On Fri, 2010-08-20 at 14:32 +0200, Jan Kiszka wrote: > Jan Kiszka wrote: > > Philippe Gerum wrote: > >> I've toyed a bit to find a generic approach for the nucleus to regain > >> complete control over a userland application running in a syscall-less > >> loop. > >> > >> The original issue was about recovering gracefully from a runaway > >> situation detected by the nucleus watchdog, where a thread would spin in > >> primary mode without issuing any syscall, but this would also apply for > >> real-time signals pending for such a thread. Currently, Xenomai rt > >> signals cannot preempt syscall-less code running in primary mode either. > >> > >> The major difference between the previous approaches we discussed about > >> and this one, is the fact that we now force the runaway thread to run a > >> piece of valid code that calls into the nucleus. We do not force the > >> thread to run faulty code or at a faulty address anymore. Therefore, we > >> can reuse this feature to improve the rt signal management, without > >> having to forge yet-another signal stack frame for this. > >> > >> The code introduced only fixes the watchdog related issue, but also does > >> some groundwork for enhancing the rt signal support later. The > >> implementation details can be found here: > >> http://git.xenomai.org/?p=xenomai-rpm.git;a=commit;h=4cf21a2ae58354819da6475ae869b96c2defda0c > >> > >> The current mayday support is only available for powerpc and x86 for > >> now, more will come in the next days. To have it enabled, you have to > >> upgrade your I-pipe patch to 2.6.32.15-2.7-00 or 2.6.34-2.7-00 for x86, > >> 2.6.33.5-2.10-01 or 2.6.34-2.10-00 for powerpc. That feature relies on a > >> new interface available from those latest patches. > >> > >> The current implementation does not break the 2.5.x ABI on purpose, so > >> we could merge it into the stable branch. > >> > >> We definitely need user feedback on this. Typically, does arming the > >> nucleus watchdog with that patch support in, properly recovers from your > >> favorite "get me out of here" situation? TIA, > >> > >> You can pull this stuff from > >> git://git.xenomai.org/xenomai-rpm.git, queue/mayday branch. > >> > > > > I've retested the feature as it's now in master, and it has one > > remaining problem: If you run the cpu hog under gdb control and try to > > break out of the while(1) loop, this doesn't work before the watchdog > > expired - of course. But if you send the break before the expiry (or hit > > a breakpoint), something goes wrong. The Xenomai task continues to spin, > > and there is no chance to kill its process (only gdb). > > > > # cat /proc/xenomai/sched > > CPU PID CLASS PRI TIMEOUT TIMEBASE STAT NAME > > 0 0 idle -1 - master RR ROOT/0
Eeek, we really need to have a look at this funky STAT output. > > 1 0 idle -1 - master R ROOT/1 > > 0 6120 rt 99 - master Tt cpu-hog > > # cat /proc/xenomai/stat > > CPU PID MSW CSW PF STAT %CPU NAME > > 0 0 0 0 0 00500088 0.0 ROOT/0 > > 1 0 0 0 0 00500080 99.7 ROOT/1 > > 0 6120 0 1 0 00342180 100.0 cpu-hog > > 0 0 0 21005 0 00000000 0.0 IRQ3340: [timer] > > 1 0 0 35887 0 00000000 0.3 IRQ3340: [timer] > > > > Fixable by this tiny change: > > diff --git a/ksrc/nucleus/sched.c b/ksrc/nucleus/sched.c > index 5242d9f..04a344e 100644 > --- a/ksrc/nucleus/sched.c > +++ b/ksrc/nucleus/sched.c > @@ -175,7 +175,8 @@ void xnsched_init(struct xnsched *sched, int cpu) > xnthread_name(&sched->rootcb)); > > #ifdef CONFIG_XENO_OPT_WATCHDOG > - xntimer_init(&sched->wdtimer, &nktbase, xnsched_watchdog_handler); > + xntimer_init_noblock(&sched->wdtimer, &nktbase, > + xnsched_watchdog_handler); > xntimer_set_name(&sched->wdtimer, "[watchdog]"); > xntimer_set_priority(&sched->wdtimer, XNTIMER_LOPRIO); > xntimer_set_sched(&sched->wdtimer, sched); > > > I.e. the watchdog timer should not be stopped by any ongoing debug > session of a Xenomai app. Will queue this for upstream. Yes, that makes a lot of sense now. The watchdog would not fire if the task was single-stepped anyway, since the latter would have been moved to secondary mode first. Did you see this bug happening in a uniprocessor context as well? > > Jan > -- Philippe. _______________________________________________ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core