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

[patchbot@xxxxxxx]

commit 0919030638e733993edb8ace762227e440a0cb65
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Tue Dec 8 08:52:31 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Dec 8 08:52:31 2020 +0100

    xen/events: do some cleanups in evtchn_fifo_set_pending()
    
    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>
    Reviewed-by: Jan Beulich <jbeulich@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);
         }
--
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