Index: head/sys/kern/subr_smp.c
===================================================================
--- head/sys/kern/subr_smp.c
+++ head/sys/kern/subr_smp.c
@@ -884,6 +884,47 @@
 #endif
 }
 
+void
+smp_rendezvous_cpus_retry(cpuset_t map,
+	void (* setup_func)(void *),
+	void (* action_func)(void *),
+	void (* teardown_func)(void *),
+	void (* wait_func)(void *, int),
+	struct smp_rendezvous_cpus_retry_arg *arg)
+{
+	int cpu;
+
+	/*
+	 * Execute an action on all specified CPUs while retrying until they
+	 * all acknowledge completion.
+	 */
+	CPU_COPY(&map, &arg->cpus);
+	for (;;) {
+		smp_rendezvous_cpus(
+		    arg->cpus,
+		    setup_func,
+		    action_func,
+		    teardown_func,
+		    arg);
+
+		if (CPU_EMPTY(&arg->cpus))
+			break;
+
+		CPU_FOREACH(cpu) {
+			if (!CPU_ISSET(cpu, &arg->cpus))
+				continue;
+			wait_func(arg, cpu);
+		}
+	}
+}
+
+void
+smp_rendezvous_cpus_done(struct smp_rendezvous_cpus_retry_arg *arg)
+{
+
+	CPU_CLR_ATOMIC(curcpu, &arg->cpus);
+}
+
 /*
  * Wait for specified idle threads to switch once.  This ensures that even
  * preempted threads have cycled through the switch function once,
Index: head/sys/sys/smp.h
===================================================================
--- head/sys/sys/smp.h
+++ head/sys/sys/smp.h
@@ -276,6 +276,19 @@
 		       void (*)(void *),
 		       void (*)(void *),
 		       void *arg);
+
+struct smp_rendezvous_cpus_retry_arg {
+	cpuset_t cpus;
+};
+void	smp_rendezvous_cpus_retry(cpuset_t,
+		       void (*)(void *),
+		       void (*)(void *),
+		       void (*)(void *),
+		       void (*)(void *, int),
+		       struct smp_rendezvous_cpus_retry_arg *);
+
+void	smp_rendezvous_cpus_done(struct smp_rendezvous_cpus_retry_arg *);
+
 #endif /* !LOCORE */
 #endif /* _KERNEL */
 #endif /* _SYS_SMP_H_ */