Index: head/sys/amd64/include/counter.h
===================================================================
--- head/sys/amd64/include/counter.h	(revision 355059)
+++ head/sys/amd64/include/counter.h	(revision 355060)
@@ -1,91 +1,92 @@
 /*-
  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
  *
  * Copyright (c) 2012 Konstantin Belousov <kib@FreeBSD.org>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
  * $FreeBSD$
  */
 
 #ifndef __MACHINE_COUNTER_H__
 #define __MACHINE_COUNTER_H__
 
 #include <sys/pcpu.h>
 
 #define	EARLY_COUNTER	&temp_bsp_pcpu.pc_early_dummy_counter
 
 #define	counter_enter()	do {} while (0)
 #define	counter_exit()	do {} while (0)
 
 #ifdef IN_SUBR_COUNTER_C
 static inline uint64_t
 counter_u64_read_one(uint64_t *p, int cpu)
 {
 
 	return (*(uint64_t *)((char *)p + UMA_PCPU_ALLOC_SIZE * cpu));
 }
 
 static inline uint64_t
 counter_u64_fetch_inline(uint64_t *p)
 {
 	uint64_t r;
 	int i;
 
 	r = 0;
 	CPU_FOREACH(i)
 		r += counter_u64_read_one((uint64_t *)p, i);
 
 	return (r);
 }
 
 static void
 counter_u64_zero_one_cpu(void *arg)
 {
 
 	*((uint64_t *)((char *)arg + UMA_PCPU_ALLOC_SIZE *
 	    PCPU_GET(cpuid))) = 0;
 }
 
 static inline void
 counter_u64_zero_inline(counter_u64_t c)
 {
 
 	smp_rendezvous(smp_no_rendezvous_barrier, counter_u64_zero_one_cpu,
 	    smp_no_rendezvous_barrier, c);
 }
 #endif
 
 #define	counter_u64_add_protected(c, i)	counter_u64_add(c, i)
 
 static inline void
 counter_u64_add(counter_u64_t c, int64_t inc)
 {
 
+	KASSERT(IS_BSP() || c != EARLY_COUNTER, ("EARLY_COUNTER used on AP"));
 	__asm __volatile("addq\t%1,%%gs:(%0)"
 	    :
 	    : "r" ((char *)c - (char *)&__pcpu[0]), "ri" (inc)
 	    : "memory", "cc");
 }
 
 #endif	/* ! __MACHINE_COUNTER_H__ */