Re: [PATCH], issue EOI to APIC prior to calling crash_kexec in die_nmi path

From: Vivek Goyal <vgoyal@redhat.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Neil Horman <nhorman@tuxdriver.com>,
	kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
	mingo@redhat.com, hpa@zytor.com, tglx@linutronix.de
Subject: Re: [PATCH], issue EOI to APIC prior to calling crash_kexec in die_nmi path
Date: Wed, 6 Feb 2008 17:48:05 -0500	[thread overview]
Message-ID: <20080206224805.GD11886@redhat.com> (raw)
In-Reply-To: <20080206220001.GA15155@elte.hu>

On Wed, Feb 06, 2008 at 11:00:01PM +0100, Ingo Molnar wrote:
> 
> * Neil Horman <nhorman@tuxdriver.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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