rtems_semaphore_obtain problems identified

Joel Sherrill joel.sherrill at oarcorp.com
Wed May 2 13:41:47 UTC 2007

Chris Johns wrote:
> Johan Zandin wrote:
>> * RTEMS bug 1237 exists in all RTEMS versions and probably
>>   on most platforms. It is related to interrupts occuring
>>   during task switches and the symptoms are that stacks
>>   may grow too large, overwriting other memory areas.
> I have looked over the patch and it only references the sparc cpu. I am 
> confused about the reference to "most platforms" reference. Do you mean just 
> sparc platforms ?
This particular scenario was that a near continuous stream of high rate 
could result in barely getting back to the interrupted task and getting 
another interrupt
and preempting from that task again and again without ever clearing off 
interrupt stack frames.

This scenario is completely possible on other CPUs but is aggravated by 
the large
interrupt stack frame on the SPARC.  I suspect that design factors in 
the _ISR_Dispatch
code that are port specific may avoid this problem on some ports.

I'm not saying it couldn't happen on another architecture just that each 
port has to
be evaluated on its own merits.  Some ports run _ISR_Dispatch at the ISR 
level of the interrupt that generated the preempt so there would be a 
known limit
on how many ISR Dispatches could stack.

The SPARC runs ISR Dispatch with all interrupts enabled so the previous ISR
is fair gain to occur again.

> Regards
> Chris
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