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

Ingo Molnar
2008-02-06T22:54:57Z

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

> 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?

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