diff --git a/xen/common/sched_null.c b/xen/common/sched_null.c
index 26c6f0f129..f90b146209 100644
--- a/xen/common/sched_null.c
+++ b/xen/common/sched_null.c
@@ -455,6 +455,7 @@ static void null_vcpu_insert(const struct scheduler *ops, struct vcpu *v)
 
     if ( unlikely(!is_vcpu_online(v)) )
     {
+        dprintk(XENLOG_G_INFO, "Not inserting %pv (not online!)\n", v);
         vcpu_schedule_unlock_irq(lock, v);
         return;
     }
@@ -516,6 +517,7 @@ static void null_vcpu_remove(const struct scheduler *ops, struct vcpu *v)
     /* If offline, the vcpu shouldn't be assigned, nor in the waitqueue */
     if ( unlikely(!is_vcpu_online(v)) )
     {
+        dprintk(XENLOG_G_INFO, "Not removing %pv (wasn't online!)\n", v);
         ASSERT(per_cpu(npc, v->processor).vcpu != v);
         ASSERT(list_empty(&nvc->waitq_elem));
         goto out;
@@ -571,14 +573,17 @@ static void null_vcpu_wake(const struct scheduler *ops, struct vcpu *v)
      */
     if ( unlikely(per_cpu(npc, cpu).vcpu != v && list_empty(&nvc->waitq_elem)) )
     {
+        cpumask_t mask;
+
+        dprintk(XENLOG_G_INFO, "%pv is waking up after having been offline\n", v);
         spin_lock(&prv->waitq_lock);
         list_add_tail(&nvc->waitq_elem, &prv->waitq);
         spin_unlock(&prv->waitq_lock);
 
-        cpumask_and(cpumask_scratch_cpu(cpu), v->cpu_hard_affinity,
+        cpumask_and(&mask, v->cpu_hard_affinity,
                     cpupool_domain_cpumask(v->domain));
 
-        if ( !cpumask_intersects(&prv->cpus_free, cpumask_scratch_cpu(cpu)) )
+        if ( !cpumask_intersects(&prv->cpus_free, &mask) )
         {
             dprintk(XENLOG_G_WARNING, "WARNING: d%dv%d not assigned to any CPU!\n",
                     v->domain->domain_id, v->vcpu_id);
@@ -595,7 +600,7 @@ static void null_vcpu_wake(const struct scheduler *ops, struct vcpu *v)
          * - if we're racing already, and if there still are free cpus, try
          *   again.
          */
-        while ( cpumask_intersects(&prv->cpus_free, cpumask_scratch_cpu(cpu)) )
+        while ( cpumask_intersects(&prv->cpus_free, &mask) )
         {
             unsigned int new_cpu = pick_cpu(prv, v);
 
@@ -635,6 +640,8 @@ static void null_vcpu_sleep(const struct scheduler *ops, struct vcpu *v)
         }
         else if ( per_cpu(npc, cpu).vcpu == v )
             tickled = vcpu_deassign(prv, v);
+
+        dprintk(XENLOG_G_INFO, "%pv is, apparently, going offline (tickled=%d)\n", v, tickled);
     }
 
     /* If v is not assigned to a pCPU, or is not running, no need to bother */
@@ -697,6 +704,8 @@ static void null_vcpu_migrate(const struct scheduler *ops, struct vcpu *v,
      */
     if ( unlikely(!is_vcpu_online(v)) )
     {
+        dprintk(XENLOG_G_INFO, "%pv is, apparently, going offline\n", v);
+
         spin_lock(&prv->waitq_lock);
         list_del_init(&nvc->waitq_elem);
         spin_unlock(&prv->waitq_lock);