linux-kernel - Re: [PATCH], issue EOI to APIC prior to calling crash_kexec in die

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Date:	Wed, 6 Feb 2008 17:48:05 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Neil Horman <nhorman@...driver.com>, tglx@...utronix.de,
	mingo@...hat.com, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, hpa@...or.com
Subject: Re: [PATCH], issue EOI to APIC prior to calling crash_kexec in
	die_nmi path

On Wed, Feb 06, 2008 at 11:00:01PM +0100, Ingo Molnar wrote:
> 
> * Neil Horman <nhorman@...driver.com> wrote:
> 
> >  	if (!user_mode_vm(regs)) {
> > +		nmi_exit();
> > +		local_irq_enable();
> >  		current->thread.trap_no = 2;
> >  		crash_kexec(regs);
> 
> looks good to me, but please move the local_irq_enable() to within 
> crash_kexec() instead - probably inside the "got the kexec lock" 
> section. That makes crash_kexec() use generally safer too i guess: right 
> it seems that die() too can call crash_kexec() with irqs disabled - and 
> can thus hang in smp_send_stop() [or wherever it hung before].
> 

In general, I think we should not be servicing interrupts once the system
has crashed and crash_kexec() has been invoked. 

In fact, right now machine_crash_shutdown() explicity disables interrupt
before sending NMIs to other cpus to stop these cpus and which makes sense to
me.

I am wondering if interrupts are disabled on crashing cpu or if crashing
cpu is inside die_nmi(), how would it stop/prevent delivery of NMI IPI to
other cpus.

Am I missing something obivious?

Thanks
Vivek
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