[xen stable-4.10] evtchn/fifo: use stable fields when recording "last queue" information

[patchbot@xxxxxxx]

commit 1fdcfdbfb2b1920a0bbaf8281cb8a7f6e37b2a6f
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Dec 1 17:34:38 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Dec 1 17:34:38 2020 +0100

    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@xxxxxxxx>
    Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>
    Reviewed-by: Paul Durrant <paul@xxxxxxx>
    master commit: 6f6f07b64cbe90e54f8e62b4d6f2404cf5306536
    master date: 2020-10-02 08:37:35 +0200
---
 xen/common/event_fifo.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xen/common/event_fifo.c b/xen/common/event_fifo.c
index 45c024739d..98742ba9cb 100644
--- 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);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.10