Philippe Gerum wrote: > On Mon, 2010-06-28 at 16:06 +0200, Jan Kiszka wrote: >> Philippe Gerum wrote: >>> On Thu, 2010-06-24 at 14:05 +0200, 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). >>> I can't reproduce this easily here; it happened only once on a lite52xx, >>> and then disappeared; no way to reproduce this once on a dual core atom >>> in 64bit mode, or on a x86_32 single core platform either. But I still >>> saw it once on a powerpc target, so this looks like a generic >>> time-dependent issue. >>> >>> Do you have the same behavior on a single core config, >> You cannot reproduce it on a single core as the CPU hog will occupy that >> core and gdb cannot be operated. >> >>> and/or without >>> WARNSW enabled? >> Just tried and disabled WARNSW in the test below: no difference. >> >>> Also, could you post your hog test code? maybe there is a difference >>> with the way I'm testing. >> #include <signal.h> >> #include <native/task.h> >> #include <sys/mman.h> >> #include <stdlib.h> >> >> void sighandler(int sig, siginfo_t *si, void *context) >> { >> printf("SIGDEBUG: reason=%d\n", si->si_value.sival_int); >> exit(1); >> } >> >> void loop(void *arg) >> { >> RT_TASK_INFO info; >> >> while (1) >> if (!arg) >> rt_task_inquire(NULL, &info); >> } >> >> int main(int argc, const char *argv[]) >> { >> struct sigaction sa; >> RT_TASK task; >> >> sigemptyset(&sa.sa_mask); >> sa.sa_sigaction = sighandler; >> sa.sa_flags = SA_SIGINFO; >> sigaction(SIGDEBUG, &sa, NULL); >> >> mlockall(MCL_CURRENT|MCL_FUTURE); >> rt_task_spawn(&task, "cpu-hog", 0, 99, T_JOINABLE|T_WARNSW, loop, >> (void *)(long)((argc > 1) && strcmp(argv[1], "--lethal") == 0)); >> rt_task_join(&task); >> >> return 0; >> } > > I can't reproduce this issue, leaving the watchdog threshold to the > default value (4s). > >> CONFIG_XENO_OPT_WATCHDOG=y >> CONFIG_XENO_OPT_WATCHDOG_TIMEOUT=60 > > 60s seems way too long to have a chance of recovering from a runaway > loop to a reasonably sane state.
That's required for debugging the kernel. > Do you still see the issue with shorter > timeouts? Yes, I usually lower the timeout before triggering the issue. OK, I will try to find some time to look closer at this. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux _______________________________________________ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core
