Index: sys/kern/kern_mutex.c
===================================================================
--- sys/kern/kern_mutex.c	(revision 216290)
+++ sys/kern/kern_mutex.c	(working copy)
@@ -501,7 +501,7 @@
 _mtx_lock_spin(struct mtx *m, uintptr_t tid, int opts, const char *file,
     int line)
 {
-	int i = 0;
+	int i = 0, prtd = 1;
 #ifdef LOCK_PROFILING
 	int contested = 0;
 	uint64_t waittime = 0;
@@ -511,19 +511,34 @@
 		CTR1(KTR_LOCK, "_mtx_lock_spin: %p spinning", m);
 
 	lock_profile_obtain_lock_failed(&m->lock_object, &contested, &waittime);
+	if (m == &smp_ipi_mtx && rebooting)
+		printf("That1: %p\n", (void *)m->mtx_lock);
 	while (!_mtx_obtain_lock(m, tid)) {
 
 		/* Give interrupts a chance while we spin. */
 		spinlock_exit();
+		if (m == &smp_ipi_mtx && rebooting)
+			printf("That2: %p\n", (void *)m->mtx_lock);
 		while (m->mtx_lock != MTX_UNOWNED) {
 			if (i++ < 10000000) {
 				cpu_spinwait();
 				continue;
 			}
-			if (i < 60000000 || kdb_active || panicstr != NULL)
+			if (i < 60000000 || kdb_active || panicstr != NULL) {
+				if (m == &smp_ipi_mtx && rebooting && prtd)
+					printf("That3: %p\n",
+					    (void *)m->mtx_lock);
+					prtd = 0;
+				}
 				DELAY(1);
-			else
+			} else {
+				if (m == &smp_ipi_mtx && rebooting && prtd)
+					printf("That4: %p\n",
+					    (void *)m->mtx_lock);
+					prtd = 0;
+				}
 				_mtx_lock_spin_failed(m);
+			}
 			cpu_spinwait();
 		}
 		spinlock_enter();