From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <528A3CEB.80909@xenomai.org> Date: Mon, 18 Nov 2013 17:14:35 +0100 From: Gilles Chanteperdrix 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> <528A3918.4000902@siemens.com> In-Reply-To: <528A3918.4000902@siemens.com> Content-Type: text/plain; charset=UTF-8; format=flowed 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: Jan Kiszka Cc: xenomai@xenomai.org On 11/18/2013 04:58 PM, Jan Kiszka wrote: > 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. Have you tried to check rtdm_task_join return value and print a message if it returns an error? I believe for the task to be still running after it was expected to terminate, rtdm_task_join would have to fail, at least. -- Gilles.