diff --git a/sys/kern/kern_timeout.c b/sys/kern/kern_timeout.c
index 0fa1af6ef5a7..daa038a02040 100644
--- a/sys/kern/kern_timeout.c
+++ b/sys/kern/kern_timeout.c
@@ -160,6 +160,7 @@ struct cc_exec {
  * state for the callout processing thread on the individual CPU.
  */
 struct callout_cpu {
+	int			cc_in_callout_process;
 	struct mtx_padalign	cc_lock;
 	struct cc_exec 		cc_exec_entity[2];
 	struct callout		*cc_next;
@@ -315,6 +316,7 @@ callout_cpu_init(struct callout_cpu *cc, int cpu)
 {
 	int i;
 
+	cc->cc_in_callout_process = 0;
 	mtx_init(&cc->cc_lock, "callout", NULL, MTX_SPIN);
 	cc->cc_callwheel = malloc_domainset(sizeof(struct callout_list) *
 	    callwheelsize, M_CALLOUT,
@@ -440,6 +442,10 @@ callout_process(sbintime_t now)
 
 	cc = CC_SELF();
 	mtx_lock_spin_flags(&cc->cc_lock, MTX_QUIET);
+	if (cc->cc_in_callout_process) {
+		printf("%s: cpu %d already processing callouts! %d\n", __func__, curcpu, cc->cc_in_callout_process);
+	}
+	cc->cc_in_callout_process++;
 
 	/* Compute the buckets of the last scan and present times. */
 	firstb = callout_hash(cc->cc_lastscan);
@@ -495,6 +501,8 @@ callout_process(sbintime_t now)
 					next = cc_exec_next(cc);
 					cc_exec_next(cc) = NULL;
 				} else {
+					if (cc_exec_next(cc) == c)
+						printf("%s: removing cc next!\n", __func__);
 					LIST_REMOVE(c, c_links.le);
 					TAILQ_INSERT_TAIL(&cc->cc_expireq,
 					    c, c_links.tqe);
@@ -534,6 +542,8 @@ callout_process(sbintime_t now)
 	cc->cc_firstevent = last;
 	cpu_new_callout(curcpu, last, first);
 
+	cc->cc_in_callout_process--;
+
 #ifdef CALLOUT_PROFILING
 	avg_depth_dir += (depth_dir * 1000 - avg_depth_dir) >> 8;
 	avg_mpcalls_dir += (mpcalls_dir * 1000 - avg_mpcalls_dir) >> 8;