The next one of the wscons(4) devices.

Index: sys/dev/wscons/wsmux.c
===================================================================
RCS file: /cvs/src/sys/dev/wscons/wsmux.c,v
retrieving revision 1.60
diff -u -p -r1.60 wsmux.c
--- sys/dev/wscons/wsmux.c	30 Dec 2024 02:46:00 -0000	1.60
+++ sys/dev/wscons/wsmux.c	21 Jan 2025 21:09:22 -0000
@@ -208,7 +208,7 @@ wsmuxopen(dev_t dev, int flags, int mode
 		return (EBUSY);
 
 	evar = &sc->sc_base.me_evar;
-	if (wsevent_init(evar))
+	if (wsevent_init_flags(evar, WSEVENT_MPSAFE))
 		return (EBUSY);
 #ifdef WSDISPLAY_COMPAT_RAWKBD
 	sc->sc_rawkbd = 0;
@@ -385,7 +385,7 @@ wsmux_do_ioctl(struct device *dv, u_long
 	struct wsmux_softc *sc = (struct wsmux_softc *)dv;
 	struct wsevsrc *me;
 	int error, ok;
-	int s, put, get, n;
+	int put, get, n;
 	struct wseventvar *evar;
 	struct wscons_event *ev;
 	struct wsmux_device_list *l;
@@ -415,13 +415,12 @@ wsmux_do_ioctl(struct device *dv, u_long
 			return (0);
 		}
 
-		s = spltty();
+		mtx_enter(&evar->ws_mtx);
 		get = evar->ws_get;
 		put = evar->ws_put;
 		ev = &evar->ws_q[put];
 		if (++put % WSEVENT_QSIZE == get) {
-			put--;
-			splx(s);
+			mtx_leave(&evar->ws_mtx);
 			return (ENOSPC);
 		}
 		if (put >= WSEVENT_QSIZE)
@@ -429,8 +428,8 @@ wsmux_do_ioctl(struct device *dv, u_long
 		*ev = *(struct wscons_event *)data;
 		nanotime(&ev->time);
 		evar->ws_put = put;
-		WSEVENT_WAKEUP(evar);
-		splx(s);
+		mtx_leave(&evar->ws_mtx);
+		wsevent_wakeup(evar);
 		return (0);
 	case WSMUXIO_ADD_DEVICE:
 #define d ((struct wsmux_device *)data)
@@ -496,7 +495,9 @@ wsmux_do_ioctl(struct device *dv, u_long
 		evar = sc->sc_base.me_evp;
 		if (evar == NULL)
 			return (EINVAL);
+		mtx_enter(&evar->ws_mtx);
 		evar->ws_async = *(int *)data != 0;
+		mtx_leave(&evar->ws_mtx);
 		return (0);
 	case FIOGETOWN:
 	case TIOCGPGRP: