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

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Message-ID: <20110822152318.GC2067@redhat.com>
Date:	Mon, 22 Aug 2011 11:23:18 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	x86@...nel.org, Andi Kleen <andi@...stfloor.org>,
	Robert Richter <robert.richter@....com>, ying.huang@...el.com,
	LKML <linux-kernel@...r.kernel.org>, jason.wessel@...driver.com
Subject: Re: [RFC][PATCH 2/6] x86, nmi: create new NMI handler routines

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

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