Re: CPU Hotplug: Hotplug Script And SIGPWR

[Nick Piggin]

Tim Hockin wrote:

> 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.

(or OOM killed being another that comes to mind)

It is sometimes inevitable. With that knowledge we should be designing
for graceful failure.

> > > 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.

Not if the application is designed to handle it. How would hotplug
scripts make this any different, anyway?

>  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.

Rusty thought you just wouldn't send it unless the process was handling
it.


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