From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <559D1D2B.3080704@siemens.com> Date: Wed, 08 Jul 2015 14:52:59 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <558579E2.9070507@web.de> <559B9B77.3020409@xenomai.org> <559BCBDB.7080208@xenomai.org> <559CFBE7.3050802@siemens.com> <559D0FEC.8030606@xenomai.org> <559D1689.2020102@siemens.com> <20150708123205.GM20176@hermes.click-hack.org> <559D189A.8060800@siemens.com> <559D1B05.9010503@xenomai.org> In-Reply-To: <559D1B05.9010503@xenomai.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai] Mayday issues again List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Philippe Gerum , Gilles Chanteperdrix Cc: Xenomai On 2015-07-08 14:43, Philippe Gerum wrote: > On 07/08/2015 02:33 PM, Jan Kiszka wrote: >> On 2015-07-08 14:32, Gilles Chanteperdrix wrote: >>> On Wed, Jul 08, 2015 at 02:24:41PM +0200, Jan Kiszka wrote: >>>> On 2015-07-08 13:56, Philippe Gerum wrote: >>>>> On 07/08/2015 12:31 PM, Jan Kiszka wrote: >>>>>> On 2015-07-07 14:53, Philippe Gerum wrote: >>>>>>> On 07/07/2015 11:27 AM, Philippe Gerum wrote: >>>>>>>> I tested the patch on ARM. Enabling IPIPE_DEBUG_INTERNAL there reveals a >>>>>>>> bug with the mayday handler now turning hw IRQs on, as a result of >>>>>>>> relaxing over the low level IRQ trampoline, which makes some I-pipe call >>>>>>>> in the irq_handler boilerplate code unhappy. The very same issue is >>>>>>>> looming on x86, with an unprotected call to __ipipe_root_p from >>>>>>>> __ipipe_handle_irq(). Disabling IRQs before leaving the mayday handler >>>>>>>> is required at the very least. >>>>>>>> >>>>>>> >>>>>>> Looking further, ARM is affected because it does not invoke >>>>>>> __ipipe_call_mayday() for triggering the mayday trap, but still uses the >>>>>>> open-coded method. This routine preserves the current hw state across >>>>>>> the trap, which should make x86 safe in the end. >>>>>> >>>>>> Which kernel version are you testing? It's not reproducing on 3.14 for >>>>>> Cortex-A7/15 targets at least. And I find __ipipe_call_mayday in both >>>>>> 3.14 and 3.18 (fastcall_exit_check). >>>>>> >>>>> >>>>> Looking at the code, any kernel version since 3.10 will have the same >>>>> issue, older ones likely too, tested on 3.18.12. This does not depend on >>>>> the ARM target. >>>>> >>>>> irq_handler from entry-armv.S: >>>>> => __ipipe_grab_irq (or indirecty via ipipe_handle_multi_irq with >>>>> MULTI_IRQ enabled) >>>>> => __ipipe_exit_irq (open coded __ipipe_notify_trap(MAYDAY), >>>>> xnthread_relax() re-enables hw IRQs) >>>>> => __ipipe_check_root_interruptible (from irq_handler) >>>>> BAD: __ipipe_root_p tested with CPU migration enabled >>>>> >>>> >>>> Maybe [1] makes the difference here? I think I had to fix this for a >>>> different reason. >>> >>> Except this does not work over legacy kernel thread stacks.. >> >> Xenomai 2 is out of scope for these changes on mayday and for gdb >> improvements. >> > > Testing CONFIG_IPIPE_LEGACY for such change would be required then. Do you mean if I can access preempt_count() in __ipipe_check_percpu_access? We are over the root domain at that point, thus legacy RT kernel threads are implicitly excluded, no? Otherwise, the changes affect only the Xenomai 3 code base anyway. Jan -- Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux