Re: [RFC] Migrating net/sched to new module interface

[Werner Almesberger <wa@almesberger.net>]

Roman Zippel wrote:
> Let's stay at the main problem, we have find out when it's safe to delete 
> an object. For dynamic objects you have the following options:
[...]
> Static objects and functions are freed by the module code and usually we
[...]

Okay so far.

> If we exclude the possibly-wait-forever-option, do you see the problem 
> for dynamic objects which also contain references to static data/
> functions?

You mean that two locking mechanisms are used, where one of them
shouldn't be doing all that much ? Well, yes.

Now, is this a problem, or just a symptom ? I'd say it's a symptom:
we already have a perfectly good locking/synchronization method,
and that's through the register/unregister interface, so the
module-specific part is unnecessary.

That much about the theory. Of course, in real life, we have to
face a few more problems:

 - if callbacks can happen after apparently successful "unregister",
   we die
 - if accesses to other static data owned by a module can happen
   after apparently successful "unregister", we may die
 - if a module doesn't "unregister" at all, we die too

But all these problems equally affect code that does other things
that can break a callback/access, e.g. if we destroy *de->data
immediately after remove_proc_entry returns.

So this is not a module-specific problem.

Agreed ?

- Werner

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