From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <528A3918.4000902@siemens.com> Date: Mon, 18 Nov 2013 16:58:16 +0100 From: Jan Kiszka MIME-Version: 1.0 References: <528A156C.1070501@xenomai.org> <528A21A9.9050502@siemens.com> <528A2486.4030606@xenomai.org> <528A2567.2000105@siemens.com> <528A27AF.3060608@xenomai.org> <528A2BB3.9040902@siemens.com> <528A2F96.7080302@xenomai.org> In-Reply-To: <528A2F96.7080302@xenomai.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai] [Xenomai-git] Jan Kiszka : switchtest: Account for invalid last_switch.from field List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: xenomai@xenomai.org On 2013-11-18 16:17, Gilles Chanteperdrix wrote: > On 11/18/2013 04:01 PM, Jan Kiszka wrote: >> On 2013-11-18 15:43, Gilles Chanteperdrix wrote: >>> On 11/18/2013 03:34 PM, Jan Kiszka wrote: >>>> On 2013-11-18 15:30, Gilles Chanteperdrix wrote: >>>>> On 11/18/2013 03:18 PM, Jan Kiszka wrote: >>>>>> On 2013-11-18 14:26, Gilles Chanteperdrix wrote: >>>>>>> On 11/18/2013 01:41 PM, git repository hosting wrote: >>>>>>>> Module: xenomai-jki >>>>>>>> Branch: for-forge >>>>>>>> Commit: 3e6d8ff9a99262e78655329dc043aacc607eb158 >>>>>>>> URL: >>>>>>>> http://git.xenomai.org/?p=xenomai-jki.git;a=commit;h=3e6d8ff9a99262e78655329dc043aacc607eb158 >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> Author: Jan Kiszka >>>>>>>> Date: Mon Nov 18 13:19:34 2013 +0100 >>>>>>>> >>>>>>>> switchtest: Account for invalid last_switch.from field >>>>>>>> >>>>>>>> If we close a test device early, no switch may have yet taken place >>>>>>>> when >>>>>>>> the first call to rtswitch_to_rt/nrt happens. This can cause >>>>>>>> to_idx to >>>>>>>> become -1, and the system will crash. Handle this corner case >>>>>>>> gracefully. >>>>>>>> >>>>>>>> Signed-off-by: Jan Kiszka >>>>>>>> >>>>>>>> --- >>>>>>>> >>>>>>>> kernel/drivers/testing/switchtest.c | 10 ++++++++-- >>>>>>>> 1 file changed, 8 insertions(+), 2 deletions(-) >>>>>>>> >>>>>>>> diff --git a/kernel/drivers/testing/switchtest.c >>>>>>>> b/kernel/drivers/testing/switchtest.c >>>>>>>> index 6f77ee9..7d17c5f 100644 >>>>>>>> --- a/kernel/drivers/testing/switchtest.c >>>>>>>> +++ b/kernel/drivers/testing/switchtest.c >>>>>>>> @@ -147,8 +147,11 @@ static int rtswitch_to_rt(rtswitch_context_t >>>>>>>> *ctx, >>>>>>>> >>>>>>>> /* to == from is a special case which means >>>>>>>> "return to the previous task". */ >>>>>>>> - if (to_idx == from_idx) >>>>>>>> + if (to_idx == from_idx) { >>>>>>>> to_idx = ctx->error.last_switch.from; >>>>>>>> + if (to_idx == -1) >>>>>>>> + return -EINVAL; >>>>>>>> + } >>>>>>> >>>>>>> I do not see how we can reach rtswitch_to_rt without having switched >>>>>>> context, since the first task to run is not an rt task. >>>>>> >>>>>> Counter question: What should enforce this ordering? And via which >>>>>> call >>>>>> stack should last_switch.from be first updated? >>>>>> >>>>>> I suspect that the RT tasks overtake the non-RT one here, but - >>>>>> granted >>>>>> - I didn't understand the control flow and synchronization of this >>>>>> driver yet. >>>>> >>>>> At any time, there is at most one task running on each cpu. This task >>>>> then switches to every other task, in turn. The first task to run >>>>> is the >>>>> "sleeper" task, which calls nanosleep in order to avoid the system >>>>> to be >>>>> completely paralized. >>>>> >>>>> For instance, with 3 tasks you would get: >>>>> 1(sleeper) >>>>> 2 >>>>> 3 >>>>> 1(sleeper) >>>>> 3 >>>>> 2 >>>>> 1(sleeper) >>>>> 2 >>>>> 3 >>>>> >>>>> etc... >>>> >>>> Ah, maybe this is the real bug: >>>> >>>> diff --git a/kernel/drivers/testing/switchtest.c >>>> b/kernel/drivers/testing/switchtest.c >>>> index 7d17c5f..b5080a6 100644 >>>> --- a/kernel/drivers/testing/switchtest.c >>>> +++ b/kernel/drivers/testing/switchtest.c >>>> @@ -404,7 +404,8 @@ static void rtswitch_ktask(void *cookie) >>>> >>>> to = task->base.index; >>>> >>>> - rtswitch_pend_rt(ctx, task->base.index); >>>> + if (rtswitch_pend_rt(ctx, task->base.index) != 0) >>>> + return; >>>> >>>> for(;;) { >>>> if (task->base.flags & RTTST_SWTEST_USE_FPU) >>>> >>>> Still need to validate, will let you know. >>> >>> I do not think that it is the right fix either: we should not have an >>> error in a ktask, because they are destroyed before anything else is >>> destroyed. >> >> Not an error, a destroyed rtdm event, thus return code < 0. This didn't >> matter so far as we kill the kernel task where it was blocked. Now it >> has to properly leave its main function. > > The rtdm event is destroyed after the ktask. So, normally, this should > not happen. True. OK, but rtdm_task_destroy calls xnthread_cancel, and that should kick us out of rtdm_event_wait with -EINTR - to my understanding. In any case, the patch didn't help. Trying to get some traces now for a better picture. Jan -- Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux