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Fri Jun 26 00:39:13 UTC 2015

I mean not recursion. just looping till top of stack of held mutexes.
check this out:
-->updateRecPriority() line 143

Thanks,

On Thu, Jun 25, 2015 at 5:35 PM, Joel Sherrill <joel.sherrill at oarcorp.com>
wrote:

>
>
> On June 25, 2015 7:33:24 PM CDT, Saurabh Gadia <gadia at usc.edu> wrote:
> >@joel: It essentially means finding out the highest priority thread (or
> >ceiling) of any remaining mutex held, right?
> >
> >If you are talking this in context of nested mutex problem --->
> >
> >We never go and find the highest priority thread waiting on held mutex.
> >Inversely highest priority thread will recursively make changes to top
> >of stack of held mutexes by the holder. We don't search.
>
> True recursion? Or implemented with loop?
>
> Ok. Still an O(n) operation. Discuss locking on devel@
>
> >
> >Thanks,
> >
> >
> >
> >
> >On Thu, Jun 25, 2015 at 5:27 PM, Joel Sherrill
> ><joel.sherrill at oarcorp.com> wrote:
> >
> >
> >
> >On June 25, 2015 7:23:06 PM CDT, Cyrille Artho
> ><cyrille.artho at gmail.com> wrote:
> >>Hi Gedare and all,
> >>Good news:
> >>In this morning's discussion, we fixed some remaining issues in the
> >>model and now got results.
> >>
> >>The current model shows a case of priority inversion with a simple
> >>priority reset mechanism and the absence of that problem with the
> >>proposed strategy.
> >>
> >>There is only one flaw: We had to use a global lock in the model
> >>(essentially making the entire "lock" and "unlock" operations atomic),
> >>because so far we couldn't find a way to secure lock the operations on
> >>a lower level. The model uses a list of locks held (by a thread) and a
> >>list of threads waiting on a lock (in the lock data structure), so
> >>these aspects are essentially cross-cutting and very hard to get right
> >>without a global lock.
> >>
> >>The RTEMS code uses different macros inside these operations (_Seize,
> >>_Surrender), which do not seem to use a global lock (but I may have
> >>missed something). It is possible that a data race occurs for a
> >>complex lock update strategy, if we don't use a global lock.
> >>
> >>Saurabh will clean up the model and provide documentation with
> >details.
> >>
> >>In the meantime, can you maybe answer these questions for us:
> >>
> >>(1) Did you have any issues with race conditions in the current RTEMS
> >>code (especially recent changes)?
> >
> >We haven't observed any but that doesn't mean there aren't any
> >undiscovered.
> >
> >>(2) Is a fix using a global lock acceptable? Correctness-wise it's the
> >>safest thing, but of course performance-wise it's a bottleneck.
> >
> >The locking strategy needs to be discussed. On a uniprocessor system,
> >these issues tend to be minor and cause delays. On smp systems, they
> >become more complex and performance problems.
> >
> >It essentially means finding out the highest priority thread (or
> >ceiling) of any remaining mutex held, right?
> >
> >Bring this up on devel@
> >
> >
> >--joel
>
> --joel
>
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