Re: CPU Hotplug: Hotplug Script And SIGPWR

[Tim Hockin <thockin@hockin.org>]

On Tue, Jan 20, 2004 at 07:14:12PM +1100, Nick Piggin wrote:
> >Under what conditions?  Not arbitrary entropy, surely.  If a hotplug script
> >is present and does not blow up, it should be safe to assume it will be run
> >upon an event being delivered.  If not, we have a WAY bigger problem :)
> >
> 
> That assumption is not safe. The main problems are of course process limits
> and memory allocation failure.

If root has a process limit that make hotplug scripts fail to run, then
we're hosed in a lot of ways.  And if we fail to allocate memory, there
really ought to be some retry or something.  It seems to me that a failure
to run a hotplug script is a BAD THING.

> >Sending it a SIGPWR means you have to run it on a different CPU that it was
> >affined to, which is already a violation.
> 
> At least the task has the option to handle the problem.

But it is a violation of the affinity.  As the kernel we CAN NOT know what
the affinity really means.  Maybe there is some way for a task to indicate
it would like to receive SIGPWR in that case.  Or some other signal.  Can we
invent new signals?

That way a task that KNOWS about the CPU disappearing underneath it can be
wise, while everything else will not just get killed.