Index: sys/compat/linuxkpi/common/include/linux/timer.h
===================================================================
--- sys/compat/linuxkpi/common/include/linux/timer.h
+++ sys/compat/linuxkpi/common/include/linux/timer.h
@@ -78,12 +78,12 @@
 	callout_init(&(timer)->callout, 1);			\
 } while (0)
 
-extern void mod_timer(struct timer_list *, int);
+extern int mod_timer(struct timer_list *, int);
 extern void add_timer(struct timer_list *);
 extern void add_timer_on(struct timer_list *, int cpu);
 extern int del_timer(struct timer_list *);
+extern int del_timer_sync(struct timer_list *);
 
-#define	del_timer_sync(timer)	(void)callout_drain(&(timer)->callout)
 #define	timer_pending(timer)	callout_pending(&(timer)->callout)
 #define	round_jiffies(j)	\
 	((int)(((j) + linux_timer_hz_mask) & ~linux_timer_hz_mask))
Index: sys/compat/linuxkpi/common/src/linux_compat.c
===================================================================
--- sys/compat/linuxkpi/common/src/linux_compat.c
+++ sys/compat/linuxkpi/common/src/linux_compat.c
@@ -1903,14 +1903,19 @@
 	timer->function(timer->data);
 }
 
-void
+int
 mod_timer(struct timer_list *timer, int expires)
 {
+	int ret;
 
 	timer->expires = expires;
-	callout_reset(&timer->callout,
+	ret = callout_reset(&timer->callout,
 	    linux_timer_jiffies_until(expires),
 	    &linux_timer_callback_wrapper, timer);
+
+	MPASS(ret == 0 || ret == 1);
+
+	return (ret == 1);
 }
 
 void
@@ -1940,6 +1945,15 @@
 	return (1);
 }
 
+int
+del_timer_sync(struct timer_list *timer)
+{
+
+	if (callout_drain(&(timer)->callout) == -1)
+		return (0);
+	return (1);
+}
+
 /* greatest common divisor, Euclid equation */
 static uint64_t
 lkpi_gcd_64(uint64_t a, uint64_t b)