From mboxrd@z Thu Jan  1 00:00:00 1970
References: <CAOuPNLjGFNwaCNa1zGQY4gZpLC7J=5M4EzGNS-YiK1UOx=+t0w@mail.gmail.com>
 <d8ad5e99-4097-4754-f443-de74f9653cb4@xenomai.org>
 <CAOuPNLgYEpHaoMMZ+Dx=WHqwMnRLwkx_hUZAj6Jtiqfq_1LTZw@mail.gmail.com>
From: Philippe Gerum <rpm@xenomai.org>
Message-ID: <5e40ba43-e8a0-1a2e-9020-d62788ad7c01@xenomai.org>
Date: Wed, 28 Mar 2018 19:32:42 +0200
MIME-Version: 1.0
In-Reply-To: <CAOuPNLgYEpHaoMMZ+Dx=WHqwMnRLwkx_hUZAj6Jtiqfq_1LTZw@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Subject: Re: [Xenomai] Problem with rt_cond_wait and rt_cond_signal
 combination
List-Id: Discussions about the Xenomai project <xenomai.xenomai.org>
List-Unsubscribe: <https://xenomai.org/mailman/options/xenomai>,
 <mailto:xenomai-request@xenomai.org?subject=unsubscribe>
List-Archive: <http://xenomai.org/pipermail/xenomai/>
List-Post: <mailto:xenomai@xenomai.org>
List-Help: <mailto:xenomai-request@xenomai.org?subject=help>
List-Subscribe: <https://xenomai.org/mailman/listinfo/xenomai>,
 <mailto:xenomai-request@xenomai.org?subject=subscribe>
To: Pintu Kumar <pintu.ping@gmail.com>
Cc: "Xenomai@xenomai.org" <xenomai@xenomai.org>

On 03/28/2018 07:20 PM, Pintu Kumar wrote:
> On Wed, Mar 28, 2018 at 8:37 PM, Philippe Gerum <rpm@xenomai.org> wrote:
>> On 03/28/2018 09:54 AM, Pintu Kumar wrote:
>>> Hi,
>>>
>>> We are facing one issue on Xenomai-3 on x86_64 system.
>>> Kernel: 4.9.51
>>> ipipe version: 4
>>> # /usr/xenomai/sbin/version
>>> Xenomai/cobalt v3.0.6 -- #5956064 (2018-03-20 12:13:33 +0100)
>>>
>>> Its a very simple API level test.
>>> We create a condition variable and wait for the condition inside a task.
>>> Then, we immediately signal the condition from the main thread, and simply
>>> wait for the test to finish.
>>>
>>> But we observed that condition task is never getting released, and the
>>> program hangs.
>>>
>>> This is the output:
>>> --------------------------
>>> # ./condsignal
>>> cond_task --> started
>>> main --> cond signal success: 0
>>> Waiting for task to finish....
>>> ^C
>>>
>>>
>>> This is the code snippet that was used.
>>> -----------------------------------------------------
>>> # cat condsignal.c
>>>
>>> /*
>>>  * 1. Create an condition variable and wait inside a task.
>>>  * 2. Delete the condition variable from main task.
>>>  * 3. Observe that the condition wait is released and task ends normally.
>>>  * 4. Finally main task should exit normally.
>>>  *
>>>  * */
>>> #include <stdio.h>
>>> #include <stdlib.h>
>>> #include <sys/mman.h>
>>> #include <alchemy/task.h>
>>> #include <alchemy/mutex.h>
>>> #include <alchemy/cond.h>
>>> #include <alchemy/task.h>
>>>
>>> static RT_COND cond;
>>> static RT_MUTEX mutex;
>>>
>>> static void cond_task(void *cookie)
>>> {
>>>         int err;
>>>
>>>         printf("%s --> started \n", __func__);
>>>         rt_mutex_acquire(&mutex, TM_INFINITE);
>>>         err = rt_cond_wait(&cond, &mutex, TM_INFINITE);
>>>         rt_mutex_release(&mutex);
>>>         if (err) {
>>>                 printf("rt_cond_wait failed, err = %d", err);
>>>                 return;
>>>         }
>>>         printf("%s --> cond wait done\n", __func__);
>>> }
>>>
>>> int main(int argc, char **argv)
>>> {
>>>         int err;
>>>         RT_TASK task1;
>>>
>>>         mlockall(MCL_CURRENT | MCL_FUTURE);
>>
>>         The line above is redundant with libcobalt inits. But you need:
>>
>>           err = rt_task_shadow(NULL, "main", <prio>, 0);
>>           ...
> 
> OK thank you so much for this. I will try it.
> And, yes I am debugging this issue.
> I found that rt_cond_wait_timed, did not return from here:

Ok, thanks for looking at this. The issue is that the app is missing the
call to rt_task_shadow() in the main thread. So that thread receives
-EPERM from rt_mutex_acquire(), and the rest is a fallout of that
original error.

-- 
Philippe.