From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <528A27AF.3060608@xenomai.org> Date: Mon, 18 Nov 2013 15:43:59 +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> In-Reply-To: <528A2567.2000105@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 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. Do you have the issue with switchtest alone or switchtest -s ? -- Gilles.