evtchn/fifo: use stable fields when recording "last queue" information

Both evtchn->priority and evtchn->notify_vcpu_id could change behind the
back of evtchn_fifo_set_pending(), as for it - in the case of
interdomain channels - only the remote side's per-channel lock is held.
Neither the queue's priority nor the vCPU's vcpu_id fields have similar
properties, so they seem better suited for the purpose. In particular
they reflect the respective evtchn fields' values at the time they were
used to determine queue and vCPU.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Paul Durrant <paul@xen.org>
master commit: 6f6f07b64cbe90e54f8e62b4d6f2404cf5306536
master date: 2020-10-02 08:37:35 +0200

diff --git a/xen/common/event_fifo.c b/xen/common/event_fifo.c
index 45c024739d38978252117070028f5eb55bb7727a..98742ba9cba3803fb7f3fb0d358917d1aa3cc125 100644 (file)
--- a/xen/common/event_fifo.c
+++ b/xen/common/event_fifo.c
@@ -224,8 +224,8 @@ static void evtchn_fifo_set_pending(struct vcpu *v, struct evtchn *evtchn)
         /* Moved to a different queue? */
         if ( old_q != q )
         {
-            evtchn->last_vcpu_id = evtchn->notify_vcpu_id;
-            evtchn->last_priority = evtchn->priority;
+            evtchn->last_vcpu_id = v->vcpu_id;
+            evtchn->last_priority = q->priority;
 
             spin_unlock_irqrestore(&old_q->lock, flags);
             spin_lock_irqsave(&q->lock, flags);