[PATCH] score: Critical section change in _Thread_Dispatch - CAREFUL REVIEW REQUIRED

[Joel Sherrill]

On 7/29/2013 9:17 AM, Gedare Bloom wrote:
> It seems like it should work fine, as long as the ISR does not update
> _Thread_Executing or reset the disable_level to 0  which I think would
> both be bugs anyway...
The ISR Handling code changing _Thread_Executing would be
a horrible, horrible bug. Context switches are always thread
to thread. Not ISR->thread.

The assembly ISR Handling code should only be incrementing
and decrementing disable_level.  If there are services which
do explicitly set it, then they should be forbidden from being
called in an ISR and probably reviewed for correctness given
the recent changes.

One odd thought.. Given the stated assumptions of this patch,
I wonder if RTEMS_DEBUG should enable an assertion on these
conditions at the top of _Thread_Dispatch.

I also wonder if it is worth considering RTEMS_DEBUG or
run-time errors being returned for making illegal calls during
an ISR. Adding run-time error codes will increase code size so
I tend to be against that since these are design errors.

Overall I think this is correct. You just opened the door to more
internal checks.

--joel
> On Fri, Jul 26, 2013 at 11:27 AM, Gedare Bloom <gedare at rtems.org> wrote:
>> I can look at it and think through what it means hopefully early next week.
>>
>> On Fri, Jul 26, 2013 at 10:48 AM, Sebastian Huber
>> <sebastian.huber at embedded-brains.de> wrote:
>>> Hello,
>>>
>>> please review this change carefully.  It may introduce a subtle but
>>> devastating problem.
>>>
>>> --
>>> 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
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>>>
>>> Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
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-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel.sherrill at OARcorp.com        On-Line Applications Research
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