Index: sys/kern/kern_timeout.c
===================================================================
--- sys/kern/kern_timeout.c
+++ sys/kern/kern_timeout.c
@@ -1150,7 +1150,7 @@
 	struct callout_cpu *cc, *old_cc;
 	struct lock_class *class;
 	int direct, sq_locked, use_lock;
-	int not_on_a_list;
+	int not_on_a_list, running;
 
 	if (safe)
 		WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, c->c_lock,
@@ -1378,8 +1378,15 @@
 		}
 	}
 	callout_cc_del(c, cc);
+
+	/*
+	 * If we are asked to stop a callout which is currently in progress
+	 * and indeed impossible to stop then return 0.
+	 */
+	running = !!(cc_exec_curr(cc, direct) == c);
+
 	CC_UNLOCK(cc);
-	return (1);
+	return (!running);
 }
 
 void