Index: sys/amd64/amd64/vm_machdep.c
===================================================================
--- sys/amd64/amd64/vm_machdep.c	(revision 206480)
+++ sys/amd64/amd64/vm_machdep.c	(working copy)
@@ -67,6 +67,10 @@
 #include <sys/vnode.h>
 #include <sys/vmmeter.h>
 
+#if defined(DIAGNOSTIC) && defined(KDB)
+#include <sys/kdb.h>
+#endif
+
 #include <machine/cpu.h>
 #include <machine/md_var.h>
 #include <machine/pcb.h>
@@ -520,13 +524,31 @@
 cpu_reset()
 {
 #ifdef SMP
-	u_int cnt, map;
+	u_int cnt, map, sb;
 
 	if (smp_active) {
 		map = PCPU_GET(other_cpus) & ~stopped_cpus;
 		if (map != 0) {
 			printf("cpu_reset: Stopping other CPUs\n");
 			stop_cpus(map);
+			sb = 0;
+#ifdef DIAGNOSTIC
+			while ((stopped_cpus & map) != map) {
+				if (sb++ < 100000)
+					cpu_spinwait();
+				if (sb == 3000000) {
+		printf("cpu_reset: Deadlock while stopping other CPUs (0x%x)\n",
+					    map - (map & stopped_cpus));
+		printf("cpu_reset: Retry with an hard stop\n");
+					stop_cpus_hard(map -
+					    (map & stopped_cpus));
+#ifdef KDB
+					kdb_enter(KDB_WHY_UNSET,
+					    "deadlock on cpu_reset");
+#endif
+				}
+			}
+#endif
 		}
 
 		if (PCPU_GET(cpuid) != 0) {