From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4C234A15.2030708@domain.hid> Date: Thu, 24 Jun 2010 14:05:41 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <4C0692A9.2080806@domain.hid> <1276080083.18906.52.camel@domain.hid> In-Reply-To: <1276080083.18906.52.camel@domain.hid> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-core] [PATCH] Mayday support List-Id: Xenomai life and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Philippe Gerum Cc: xenomai@xenomai.org, Tschaeche IT-Services 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 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] Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux