Index: head/sys/x86/x86/mp_x86.c
===================================================================
--- head/sys/x86/x86/mp_x86.c
+++ head/sys/x86/x86/mp_x86.c
@@ -1084,6 +1084,11 @@
 
 	kcsan_cpu_init(cpuid);
 
+	/*
+	 * Assert that smp_after_idle_runnable condition is reasonable.
+	 */
+	MPASS(PCPU_GET(curpcb) == NULL);
+
 	sched_throw(NULL);
 
 	panic("scheduler returned us to %s", __func__);
@@ -1098,7 +1103,7 @@
 
 	for (cpu = 1; cpu < mp_ncpus; cpu++) {
 		pc = pcpu_find(cpu);
-		while (atomic_load_ptr(&pc->pc_curthread) == (uintptr_t)NULL)
+		while (atomic_load_ptr(&pc->pc_curpcb) == (uintptr_t)NULL)
 			cpu_spinwait();
 		kmem_free((vm_offset_t)bootstacks[cpu], kstack_pages *
 		    PAGE_SIZE);