xen: Introduce vcpu_sleep_nosync_locked()

There are a lot of places which release a lock before calling
vcpu_sleep_nosync(), which then just grabs the lock again.  This is
not only a waste of time, but leads to more code duplication (since
you have to copy-and-paste recipes rather than calling a unified
function), which in turn leads to an increased chance of bugs.

Introduce vcpu_sleep_nosync_locked(), which can be called if you
already hold the schedule lock.

Signed-off-by: George Dunlap <george.dunlap@citrix.com>
Reviewed-by: Dario Faggioli <dfaggioli@suse.com>
Release-acked-by: Juergen Gross <jgross@suse.com>

xen/common/schedule.c

@@ -455,6 +455,19 @@ void sched_destroy_domain(struct domain *d)
     }
 }
 
+void vcpu_sleep_nosync_locked(struct vcpu *v)
+{
+    ASSERT(spin_is_locked(per_cpu(schedule_data,v->processor).schedule_lock));
+
+    if ( likely(!vcpu_runnable(v)) )
+    {
+        if ( v->runstate.state == RUNSTATE_runnable )
+            vcpu_runstate_change(v, RUNSTATE_offline, NOW());
+
+        SCHED_OP(vcpu_scheduler(v), sleep, v);
+    }
+}
+
 void vcpu_sleep_nosync(struct vcpu *v)
 {
     unsigned long flags;
@@ -464,13 +477,7 @@ void vcpu_sleep_nosync(struct vcpu *v)
 
     lock = vcpu_schedule_lock_irqsave(v, &flags);
 
-    if ( likely(!vcpu_runnable(v)) )
-    {
-        if ( v->runstate.state == RUNSTATE_runnable )
-            vcpu_runstate_change(v, RUNSTATE_offline, NOW());
-
-        SCHED_OP(vcpu_scheduler(v), sleep, v);
-    }
+    vcpu_sleep_nosync_locked(v);
 
     vcpu_schedule_unlock_irqrestore(lock, flags, v);
 }