Initially Locked Priority Ceiling Semaphores

[Joel Sherrill]

On 5/21/2014 10:35 AM, Gedare Bloom wrote:
> On Wed, May 21, 2014 at 11:08 AM, Sebastian Huber
> <sebastian.huber at embedded-brains.de> wrote:
>> On 2014-05-21 17:01, Gedare Bloom wrote:
>>>>    if ( initially_locked ) {
>>>>>     the_mutex->nest_count = 1;
>>>>>     the_mutex->holder     = executing;
>>>>>     if ( _CORE_mutex_Is_inherit_priority( &the_mutex->Attributes ) ||
>>>>>          _CORE_mutex_Is_priority_ceiling( &the_mutex->Attributes ) ) {
>>>>>
>>>>>       if ( executing->current_priority <
>>>>>              the_mutex->Attributes.priority_ceiling )
>>>>>        return CORE_MUTEX_STATUS_CEILING_VIOLATED;
>>> Looks like this check ensures the executing thread has got priority at
>>> least at the priority_ceiling. If it does not, the mutex is not
>>> initialized.
>>
>> Yes, this is the error case.   In the good case the priority is not changed
>> to the ceiling priority like for a normal rtems_semaphore_obtain() (see
>> _CORE_mutex_Seize_interrupt_trylock_body()).
>>
> Ah. Then I think your suspicion is correct. Probably the executing
> thread should be given the priority_ceiling, otherwise there can be
> some priority inversion while the initial lock is held.
Good catch.  Create a simple test case and verify it is broken.
This should have a PR with the test case and fix.
>> --
>> Sebastian Huber, embedded brains GmbH
>>
>> Address : Dornierstr. 4, D-82178 Puchheim, Germany
>> Phone   : +49 89 189 47 41-16
>> Fax     : +49 89 189 47 41-09
>> E-Mail  : sebastian.huber at embedded-brains.de
>> PGP     : Public key available on request.
>>
>> Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
> _______________________________________________
> rtems-devel mailing list
> rtems-devel at rtems.org
> http://www.rtems.org/mailman/listinfo/rtems-devel

-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel.sherrill at OARcorp.com        On-Line Applications Research
Ask me about RTEMS: a free RTOS  Huntsville AL 35805
Support Available                (256) 722-9985