Re: [RFC][PATCH 2/6] x86, nmi: create new NMI handler routines

Don Zickus
2011-08-22T15:23:29Z

On Mon, Aug 22, 2011 at 04:16:20PM +0200, Peter Zijlstra wrote:
> On Fri, 2011-08-19 at 16:37 -0400, Don Zickus wrote:
> > +static struct nmiaction *__free_nmi(unsigned int type, const char *name)
> > +{
> > + struct nmi_desc *desc = nmi_to_desc(type);
> > + struct nmiaction *n, **np = &(desc->head);
> > + unsigned long flags;
> > +
> > + spin_lock_irqsave(&desc->lock, flags);
> > +
> ...
> > +
> > + spin_unlock_irqrestore(&desc->lock, flags);
> > + synchronize_rcu();
> > + return *np;
> > +}
>
> > +void unregister_nmi_handler(unsigned int type, const char *name)
> > +{
> > + kfree(__free_nmi(type, name));
> > +}
>
> This code is weird.. why not have the kfree() in __free_nmi(), also why
> use sync_rcu() and not use kfree_rcu()?

It's a mixture of copying the notifier code and not fully understanding
the rcu options out there. I'll look into kfree_rcu and try to clean this
up.

>
> > +EXPORT_SYMBOL_GPL(unregister_nmi_handler);
>
> *g*, so binary modules can register an NMI handler, but can't unregister
> it..?

heh. I suck. Sorry about that.

Cheers,
Don