From mboxrd@z Thu Jan 1 00:00:00 1970 From: Philippe Gerum In-Reply-To: <20100609133841.GA24216@domain.hid> References: <4C0692A9.2080806@domain.hid> <1276080083.18906.52.camel@domain.hid> <20100609133841.GA24216@domain.hid> Content-Type: text/plain; charset="UTF-8" Date: Wed, 09 Jun 2010 16:01:11 +0200 Message-ID: <1276092071.18906.99.camel@domain.hid> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-help] [PATCH] Mayday support (was: Re: [RFC] Break out of endless user space loops) List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Tschaeche IT-Services Cc: xenomai@xenomai.org On Wed, 2010-06-09 at 15:38 +0200, Tschaeche IT-Services wrote: > Not quite sure if i understood correctly. Trying to summarize: > > Triggering the syscall code (to get out of the loop) is initiated > by the nucleus watchdog (available with CONFIG_XENO_OPT_WATCHDOG) > and can't be forced manually yet. Right? Yes. > > Your (Philippe's) commit message says: > > ... > > runaway thread situation detected by the nucleus watchdog. Instead of > > killing the runaway thread bluntly, this feature allows to force a > > relax on it, despite the syscall-less nature of the code it was > > ... > > How do i choose between "killing" and "force a relax"? > Or does the watchdog already set a Linux signal, > which is handled when the task gets relaxed? > There is no more killing of the runaway task, it always get a SIGXCPU, after the nucleus forced it to relax, so that you can decide what's next, but the system does not lock up anymore. > Then, for testing, i have to do the following: > - apply patches ;-) Including the new I-pipe patch. > - setup the watchdog with an appropriate timeout > (wd_timeout_arg/CONFIG_XENO_OPT_WATCHDOG_TIMEOUT) > - no changes in our user space application > - just wait until watchdog forces relaxing the task > which will initiate linux signal handling > > correct? Correct. > > Thanks for your support, > > Olli > > On Wed, Jun 09, 2010 at 12:41:23PM +0200, 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. > > > > > > -- > > Philippe. > > > > -- Philippe.