On Tuesday 15 October 2002 05:25, Rusty Russell wrote:
> In message <E17w2XF-0005oW-00@starship> you write:
> > Not being able to unload LSM would suck enormously. At last count, we
> > knew how to do this:
> >
> > 1) Unhook the function hooks (using a call table simplifies this)
> > 2) Schedule on each CPU to ensure all tasks are out of the module
> > 3) A schedule where the module count is incremented doesn't count
> >
> > and we rely on the rule that and module code that could sleep must be
> > bracketed by inc/dec of the module count.
> >
> > Did somebody come up with a reason why this will not work?
>
> It won't quite work if the hooks can sleep. You can say "don't sleep"
> or have a wedge which does the "try_inc_mod_count()" then calls into
> the module (and returns some default if it can't inc the module count).
Right. By coincidence, I found myself thinking about this very problem
as I re-materialized this morning. If TRY_INC_MOD_COUNT also ors a flag
(which it does now, for other reasons) then:
1) Clear the mod_inc flag
2) Unhook the function hooks
3) Schedule on each CPU
4) If the mod_inc flag is set, repeat from (1)
This should perform acceptably well, and would only be done in cases
where the existing TRY_INC_MOD_COUNT strategy can't be used.
> You can't disable preemption before calling in, because there is no
> way to sleep with preemption disabled. 8(
Why is that harder than bumping a counter that makes preempt_schedule
return without doing anything?
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