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

[Gedare Bloom]

Is there a possibility an ISR happens during the
set_dispatch_level(1)? It can observe a 0-value dispatch level in that
case, and dispatch at the end of the isr?

On Mon, Jul 29, 2013 at 3:19 PM, Joel Sherrill
<joel.sherrill at oarcorp.com> wrote:
> 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
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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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