Crash in __pirq_guest_eoi()

[Jeremy Fitzhardinge <jeremy@goop.org>]

 I'm seeing a crash in:

static void __pirq_guest_eoi(struct domain *d, int pirq)
{
    struct irq_desc         *desc;
    irq_guest_action_t *action;
    cpumask_t           cpu_eoi_map;
    int                 irq;

    ASSERT(local_irq_is_enabled());
    desc = domain_spin_lock_irq_desc(d, pirq, NULL);
    if ( desc == NULL )
        return;

    action = (irq_guest_action_t *)desc->action;
    irq = desc - irq_desc;

    if ( action->ack_type == ACKTYPE_NONE )
    {

where action is NULL.

I'm playing around with the pvops kernel's handling of pirq interrupts,
so the kernel is probably misbehaving, but it would be nice if Xen
didn't keep crashing on me.

I guess this is the right fix/workaround?

diff -r d37dc6401a1f xen/arch/x86/irq.c
--- a/xen/arch/x86/irq.c	Thu Sep 02 17:44:46 2010 +0100
+++ b/xen/arch/x86/irq.c	Fri Sep 03 11:33:15 2010 -0700
@@ -1028,6 +1028,9 @@
     action = (irq_guest_action_t *)desc->action;
     irq = desc - irq_desc;
 
+    if ( action == NULL )
+	return;
+
     if ( action->ack_type == ACKTYPE_NONE )
     {
         ASSERT(!test_bit(pirq, d->pirq_mask));

    J