Re: [PATCH v2] x86/nmi: Add an emergency handler in nmi_desc & use it in nmi_shootdown_cpus()

[Waiman Long]

On 12/4/24 1:03 PM, Thomas Gleixner wrote:
> On Wed, Dec 04 2024 at 12:23, Waiman Long wrote:
> > On 12/4/24 8:10 AM, Thomas Gleixner wrote:
> > > On Tue, Dec 03 2024 at 10:07, Waiman Long wrote:
> > > > +	/*
> > > > +	 * Call the emergency handler first, if set
> > > > +	 * Emergency handler is not traced or checked by nmi_check_duration().
> > > > +	 */
> > > > +	ehandler = READ_ONCE(desc->emerg_handler);
> > > > +	if (ehandler)
> > > > +		handled = ehandler(type, regs);
> > > Shouldn't this just stop processing right here?
> > Yes in the case of crash_nmi_callback(). I suppose it is a no-return
> > call. As the emergency handler is supposed to be a general mechanism in
> > design, I don't want to make too many assumptions of what will happen
> > when the handler is invoked.
> I'm not convinced that this should be used as a general mechanism. It's
> for emergency situations and that's where it stops. If the thing
> returns, it's a bug IMO.

OK, I am fine with that. I will put a BUG_ON() after that in the next 
version.

Thanks,
Longman