Index: sys/amd64/amd64/mp_machdep.c
===================================================================
--- sys/amd64/amd64/mp_machdep.c
+++ sys/amd64/amd64/mp_machdep.c
@@ -1456,8 +1456,13 @@
 	CPU_SET_ATOMIC(cpu, &stopped_cpus);
 
 	/* Wait for restart */
-	while (!CPU_ISSET(cpu, &started_cpus))
-	    ia32_pause();
+	while (!CPU_ISSET(cpu, &started_cpus)) {
+		ia32_pause();
+
+		/* If we paniced, just stop this CPU. */
+		while (panicstr)
+			halt();
+	}
 
 	CPU_CLR_ATOMIC(cpu, &started_cpus);
 	CPU_CLR_ATOMIC(cpu, &stopped_cpus);