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

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Message-ID: <20080206225355.GB4316@elte.hu>
Date:	Wed, 6 Feb 2008 23:53:55 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Vivek Goyal <vgoyal@...hat.com>
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


* Vivek Goyal <vgoyal@...hat.com> wrote:

> 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?

i wondered about that too. kexec should be as atomic as it can be - 
enabling interrupts only opens up a window for another crash (more 
memory corruption, etc. etc) to happen.

	Ingo
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