evtchn: don't bypass unlinking pIRQ when closing port

There's no other path causing a terminal unlink_pirq_port() to be called
(evtchn_bind_vcpu() relinks it right away) and hence _if_ pirq can
indeed be NULL when closing the port, list corruption would occur when
bypassing the unlink (unless the structure never gets linked again). As
we can't come here after evtchn_destroy() anymore, (late) domain
destruction also isn't a reason for a possible exception, and hence the
only alternative looks to be that the check was pointless in the first
place. While I haven't observed the case, from code inspection I'm far
from sure I can exclude this being possible, so it feels more safe to
re-arrange the code instead.

Fixes: c24536b636f2 ("replace d->nr_pirqs sized arrays with radix tree")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Paul Durrant <paul@xen.org>

diff --git a/xen/common/event_channel.c b/xen/common/event_channel.c
index 49cb318b817149ecfc59a0f442f0bec396257f9b..161cbb77d22a86b33bef672965612f5ca4457a9d 100644 (file)
--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -614,17 +614,18 @@ int evtchn_close(struct domain *d1, int port1, bool guest)
     case ECS_PIRQ: {
         struct pirq *pirq = pirq_info(d1, chn1->u.pirq.irq);
 
-        if ( !pirq )
-            break;
-        if ( !is_hvm_domain(d1) )
-            pirq_guest_unbind(d1, pirq);
-        pirq->evtchn = 0;
-        pirq_cleanup_check(pirq, d1);
-        unlink_pirq_port(chn1, d1->vcpu[chn1->notify_vcpu_id]);
+        if ( pirq )
+        {
+            if ( !is_hvm_domain(d1) )
+                pirq_guest_unbind(d1, pirq);
+            pirq->evtchn = 0;
+            pirq_cleanup_check(pirq, d1);
 #ifdef CONFIG_X86
-        if ( is_hvm_domain(d1) && domain_pirq_to_irq(d1, pirq->pirq) > 0 )
-            unmap_domain_pirq_emuirq(d1, pirq->pirq);
+            if ( is_hvm_domain(d1) && domain_pirq_to_irq(d1, pirq->pirq) > 0 )
+                unmap_domain_pirq_emuirq(d1, pirq->pirq);
 #endif
+        }
+        unlink_pirq_port(chn1, d1->vcpu[chn1->notify_vcpu_id]);
         break;
     }