diff -r 7ada6faef565 xen/common/cpupool.c
--- a/xen/common/cpupool.c	Sun Feb 06 17:26:31 2011 +0000
+++ b/xen/common/cpupool.c	Mon Feb 07 14:26:50 2011 +0100
@@ -35,7 +35,7 @@ static DEFINE_SPINLOCK(cpupool_lock);
 
 DEFINE_PER_CPU(struct cpupool *, cpupool);
 
-#define cpupool_dprintk(x...) ((void)0)
+#define cpupool_dprintk(x...) printk(x)
 
 static struct cpupool *alloc_cpupool_struct(void)
 {
@@ -227,14 +227,30 @@ static int cpupool_assign_cpu_locked(str
     return 0;
 }
 
+static long cpupool_assign_cpu_helper(void *info)
+{
+    int cpu = cpupool_moving_cpu;
+    long ret;
+
+    cpupool_dprintk("cpupool_assign_cpu(pool=%d,cpu=%d)\n",
+                    cpupool_cpu_moving->cpupool_id, cpu);
+    BUG_ON(!is_idle_vcpu(current));
+    BUG_ON(cpu != smp_processor_id());
+    spin_lock(&cpupool_lock);
+    ret = cpupool_assign_cpu_locked(cpupool_cpu_moving, cpu);
+    spin_unlock(&cpupool_lock);
+    return ret;
+}
+
 static long cpupool_unassign_cpu_helper(void *info)
 {
     int cpu = cpupool_moving_cpu;
     long ret;
 
-    cpupool_dprintk("cpupool_unassign_cpu(pool=%d,cpu=%d) ret %ld\n",
-                    cpupool_id, cpu, ret);
-
+    cpupool_dprintk("cpupool_unassign_cpu(pool=%d,cpu=%d)\n",
+                    cpupool_cpu_moving->cpupool_id, cpu);
+    BUG_ON(!is_idle_vcpu(current));
+    BUG_ON(cpu != smp_processor_id());
     spin_lock(&cpupool_lock);
     ret = cpu_disable_scheduler(cpu);
     cpu_set(cpu, cpupool_free_cpus);
@@ -258,9 +274,51 @@ out:
 }
 
 /*
+ * assign a specific cpu to a cpupool
+ * we must be sure to run on the cpu to be assigned in idle! to achieve this
+ * the main functionality is performed via continue_hypercall_on_cpu on the
+ * specific cpu.
+ * possible failures:
+ * - cpu not free
+ * - cpu just being unplugged
+ */
+int cpupool_assign_cpu(struct cpupool *c, unsigned int cpu)
+{
+    int ret;
+
+    cpupool_dprintk("cpupool_assign_cpu(pool=%d,cpu=%d)\n",
+                    c->cpupool_id, cpu);
+
+    spin_lock(&cpupool_lock);
+    ret = -EBUSY;
+    if ( (cpupool_moving_cpu != -1) && (cpu != cpupool_moving_cpu) )
+        goto out;
+    if ( cpu_isset(cpu, cpupool_locked_cpus) )
+        goto out;
+
+    ret = 0;
+    if ( !cpu_isset(cpu, cpupool_free_cpus) && (cpu != cpupool_moving_cpu) )
+        goto out;
+
+    cpupool_moving_cpu = cpu;
+    atomic_inc(&c->refcnt);
+    cpupool_cpu_moving = c;
+    cpu_clear(cpu, c->cpu_valid);
+    spin_unlock(&cpupool_lock);
+
+    return continue_hypercall_on_cpu(cpu, cpupool_assign_cpu_helper, c);
+
+out:
+    spin_unlock(&cpupool_lock);
+    cpupool_dprintk("cpupool_assign_cpu(pool=%d,cpu=%d) ret %d\n",
+                    c->cpupool_id, cpu, ret);
+    return ret;
+}
+
+/*
  * unassign a specific cpu from a cpupool
- * we must be sure not to run on the cpu to be unassigned! to achieve this
- * the main functionality is performed via continue_hypercall_on_cpu on a
+ * we must be sure to run on the cpu to be unassigned in idle! to achieve this
+ * the main functionality is performed via continue_hypercall_on_cpu on the
  * specific cpu.
  * if the cpu to be removed is the last one of the cpupool no active domain
  * must be bound to the cpupool. dying domains are moved to cpupool0 as they
@@ -271,7 +329,6 @@ out:
  */
 int cpupool_unassign_cpu(struct cpupool *c, unsigned int cpu)
 {
-    int work_cpu;
     int ret;
     struct domain *d;
 
@@ -319,19 +376,12 @@ int cpupool_unassign_cpu(struct cpupool 
     cpu_clear(cpu, c->cpu_valid);
     spin_unlock(&cpupool_lock);
 
-    work_cpu = smp_processor_id();
-    if ( work_cpu == cpu )
-    {
-        work_cpu = first_cpu(cpupool0->cpu_valid);
-        if ( work_cpu == cpu )
-            work_cpu = next_cpu(cpu, cpupool0->cpu_valid);
-    }
-    return continue_hypercall_on_cpu(work_cpu, cpupool_unassign_cpu_helper, c);
+    return continue_hypercall_on_cpu(cpu, cpupool_unassign_cpu_helper, c);
 
 out:
     spin_unlock(&cpupool_lock);
     cpupool_dprintk("cpupool_unassign_cpu(pool=%d,cpu=%d) ret %d\n",
-                    cpupool_id, cpu, ret);
+                    c->cpupool_id, cpu, ret);
     return ret;
 }
 
@@ -345,7 +395,7 @@ int cpupool_add_domain(struct domain *d,
 {
     struct cpupool *c;
     int rc = 1;
-    int n_dom;
+    int n_dom = 0;
 
     if ( poolid == CPUPOOLID_NONE )
         return 0;
@@ -472,27 +522,15 @@ int cpupool_do_sysctl(struct xen_sysctl_
     {
         unsigned cpu;
 
+        c = __cpupool_get_by_id(op->cpupool_id, 0);
+        ret = -ENOENT;
+        if ( c == NULL )
+            break;
         cpu = op->cpu;
-        cpupool_dprintk("cpupool_assign_cpu(pool=%d,cpu=%d)\n",
-                        op->cpupool_id, cpu);
-        spin_lock(&cpupool_lock);
         if ( cpu == XEN_SYSCTL_CPUPOOL_PAR_ANY )
             cpu = first_cpu(cpupool_free_cpus);
-        ret = -EINVAL;
-        if ( cpu >= NR_CPUS )
-            goto addcpu_out;
-        ret = -EBUSY;
-        if ( !cpu_isset(cpu, cpupool_free_cpus) )
-            goto addcpu_out;
-        c = cpupool_find_by_id(op->cpupool_id, 0);
-        ret = -ENOENT;
-        if ( c == NULL )
-            goto addcpu_out;
-        ret = cpupool_assign_cpu_locked(c, cpu);
-    addcpu_out:
-        spin_unlock(&cpupool_lock);
-        cpupool_dprintk("cpupool_assign_cpu(pool=%d,cpu=%d) ret %d\n",
-                        op->cpupool_id, cpu, ret);
+        ret = (cpu < NR_CPUS) ? cpupool_assign_cpu(c, cpu) : -EINVAL;
+        cpupool_put(c);
     }
     break;