Re: simple handling of module removals Re: [OKS] Module removal

[Werner Almesberger <wa@almesberger.net>]

Brian Gerst wrote:
> PS.  If you really want to make the broken cases show themselves, poison 
> the module memory when it is unloaded.  The same can be done for dumping 
> init data and text.

Unfortunately, many of the code paths leading to the races are
sufficiently different that it's currently unlikely to actually
hit them. (E.g. it's kind of hard for some 1000+ instructions
code path to compete successfully with a cached, pre-fetched,
and pre-decoded "ret" instruction. Entry-after-removal races
(and the related data races) may be a little bit easier to catch,
but I suppose we're still talking about a likely difference of
orders of magnitude.)

I don't think preemption changes that fundamentally.
Microthreading may, and NUMA will make execution times more
variable, increasing the risk of hitting a race.

The best way to trigger such races is probably to simulate
microthreading, e.g. with an UML-SMP where only one "CPU" can
run at a time, and where execution switching is under script
control.

- Werner

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 / Werner Almesberger, Buenos Aires, Argentina         wa@almesberger.net /
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