Re: [Xenomai-core] [BUG] racy xnshadow_harden under CONFIG_PREEMPT

[Jan Kiszka <jan.kiszka@domain.hid>]

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Hannes Mayer wrote:
> Jan Kiszka wrote:
> [...]
>> PS: Out of curiosity I also checked RTAI's migration mechanism in this
>> regard. It's similar except for the fact that it does the gatekeeper's
>> work in the Linux scheduler's tail (i.e. after the next context switch).
>> And RTAI seems it suffers from the very same race. So this is either a
>> fundamental issue - or I'm fundamentally wrong.
> 
> 
> Well, most of the stuff you guys talk about in this thread is still
> beyond my level, but out of curiosity I ported the SEM example to
> RTAI (see attached sem.c)
> I couldn't come up with something similar to rt_sem_inquire and
> rt_task_inquire in RTAI (in "void output(char c)")...
> Anyway, unless I haven't missed something else important while
> porting, the example runs flawlessly on RTAI 3.3test3 (kernel 2.6.15).
> 

My claim on the RTAI race is based on quick code analysis and a bit
outdated information about its core design. I haven't tried any code to
crash it, and I guess it will take a slightly different test design to
trigger the issue there. As soon as someone could follow my reasoning
and confirm it (don't mind that you did not understand it, I hadn't
either two days ago, this is quite heavy stuff), I will inform Paolo
about this potential problem.

Jan


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