Index: head/sys/kern/kern_thread.c
===================================================================
--- head/sys/kern/kern_thread.c
+++ head/sys/kern/kern_thread.c
@@ -197,7 +197,7 @@
 
 	td = (struct thread *)mem;
 	td->td_state = TDS_INACTIVE;
-	td->td_oncpu = NOCPU;
+	td->td_lastcpu = td->td_oncpu = NOCPU;
 
 	td->td_tid = tid_alloc();
 
Index: head/sys/x86/x86/mp_x86.c
===================================================================
--- head/sys/x86/x86/mp_x86.c
+++ head/sys/x86/x86/mp_x86.c
@@ -1071,9 +1071,23 @@
 	/* NOTREACHED */
 }
 
-/*******************************************************************
- * local functions and data
- */
+static void
+smp_after_idle_runnable(void *arg __unused)
+{
+	struct thread *idle_td;
+	int cpu;
+
+	for (cpu = 1; cpu < mp_ncpus; cpu++) {
+		idle_td = pcpu_find(cpu)->pc_idlethread;
+		while (idle_td->td_lastcpu == NOCPU &&
+		    idle_td->td_oncpu == NOCPU)
+			cpu_spinwait();
+		kmem_free((vm_offset_t)bootstacks[cpu], kstack_pages *
+		    PAGE_SIZE);
+	}
+}
+SYSINIT(smp_after_idle_runnable, SI_SUB_SMP, SI_ORDER_ANY,
+    smp_after_idle_runnable, NULL);
 
 /*
  * We tell the I/O APIC code about all the CPUs we want to receive