diff --git a/sys/dev/gpio/gpioc.c b/sys/dev/gpio/gpioc.c
--- a/sys/dev/gpio/gpioc.c
+++ b/sys/dev/gpio/gpioc.c
@@ -908,27 +908,38 @@
 		res = devfs_get_cdevpriv((void **)&priv);
 		if (res != 0)
 			break;
+		mtx_lock(&priv->mtx);
 		/* If any pins have been configured, changes aren't allowed. */
 		if (!SLIST_EMPTY(&priv->pins)) {
 			res = EINVAL;
+			mtx_unlock(&priv->mtx);
 			break;
 		}
 		if (evcfg->gp_report_type != GPIO_EVENT_REPORT_DETAIL &&
 		    evcfg->gp_report_type != GPIO_EVENT_REPORT_SUMMARY) {
 			res = EINVAL;
+			mtx_unlock(&priv->mtx);
 			break;
 		}
-		priv->report_option = evcfg->gp_report_type;
 		/* Reallocate the events buffer if the user wants it bigger. */
-		if (priv->report_option == GPIO_EVENT_REPORT_DETAIL &&
+		if (evcfg->gp_report_type == GPIO_EVENT_REPORT_DETAIL &&
 		    priv->numevents < evcfg->gp_fifo_size) {
-			free(priv->events, M_GPIOC);
-			priv->numevents = evcfg->gp_fifo_size;
-			priv->events = malloc(priv->numevents *
+			void *tmp;
+
+			tmp = realloc(priv->events, evcfg->gp_fifo_size *
 			    sizeof(struct gpio_event_detail), M_GPIOC,
-			    M_WAITOK | M_ZERO);
+			    M_NOWAIT | M_ZERO);
+			if (tmp == NULL) {
+				res = ENOMEM;
+				mtx_unlock(&priv->mtx);
+				break;
+			}
+			priv->events = tmp;
+			priv->numevents = evcfg->gp_fifo_size;
 			priv->evidx_head = priv->evidx_tail = 0;
 		}
+		priv->report_option = evcfg->gp_report_type;
+		mtx_unlock(&priv->mtx);
 		break;
 	case FIONBIO:
 		/*