[PATCH v9] xen/events: do some cleanups in evtchn_fifo_set_pending()

[Juergen Gross <jgross@xxxxxxxx>]

evtchn_fifo_set_pending() can be simplified a little bit. Especially
testing for the fifo control block to exist can be moved out of the
main if clause of the function enabling to avoid testing the LINKED bit
twice.

Suggested-by: Jan Beulich <jbeulich@xxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V8:
- new patch

V9:
- move test for control_block existing to after setting PENDING bit
  (Jan Beulich)

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 xen/common/event_fifo.c | 33 +++++++++++++++------------------
 1 file changed, 15 insertions(+), 18 deletions(-)

diff --git a/xen/common/event_fifo.c b/xen/common/event_fifo.c
index a6cca4798d..d508d57219 100644
--- a/xen/common/event_fifo.c
+++ b/xen/common/event_fifo.c
@@ -229,29 +229,24 @@ static void evtchn_fifo_set_pending(struct vcpu *v, 
struct evtchn *evtchn)
         goto done;
     }
 
+    /*
+     * Control block not mapped.  The guest must not unmask an
+     * event until the control block is initialized, so we can
+     * just drop the event.
+     */
+    if ( unlikely(!v->evtchn_fifo->control_block) )
+    {
+        printk(XENLOG_G_WARNING
+               "%pv has no FIFO event channel control block\n", v);
+        goto unlock;
+    }
+
     /*
      * Link the event if it unmasked and not already linked.
      */
     if ( !guest_test_bit(d, EVTCHN_FIFO_MASKED, word) &&
-         !guest_test_bit(d, EVTCHN_FIFO_LINKED, word) )
+         !guest_test_and_set_bit(d, EVTCHN_FIFO_LINKED, word) )
     {
-        event_word_t *tail_word;
-
-        /*
-         * Control block not mapped.  The guest must not unmask an
-         * event until the control block is initialized, so we can
-         * just drop the event.
-         */
-        if ( unlikely(!v->evtchn_fifo->control_block) )
-        {
-            printk(XENLOG_G_WARNING
-                   "%pv has no FIFO event channel control block\n", v);
-            goto unlock;
-        }
-
-        if ( guest_test_and_set_bit(d, EVTCHN_FIFO_LINKED, word) )
-            goto unlock;
-
         /*
          * If this event was a tail, the old queue is now empty and
          * its tail must be invalidated to prevent adding an event to
@@ -286,6 +281,8 @@ static void evtchn_fifo_set_pending(struct vcpu *v, struct 
evtchn *evtchn)
         linked = false;
         if ( q->tail )
         {
+            event_word_t *tail_word;
+
             tail_word = evtchn_fifo_word_from_port(d, q->tail);
             linked = evtchn_fifo_set_link(d, tail_word, port);
         }
-- 
2.26.2