dev/sound: allow unplug soundcars without apps close devices

This patch fix use case: user unplug USB sound card before all apps
close /dev/mixer and /dev/dsp and then USB driver hang/wait until
all apps closed, no old devices can be removed, no new devices can be added.

dmesg show for mixer:
pcm4: unregister: mixer busy
pcm4: Waiting for sound application to exit!
And almost same for dsp, but also prints app pid.

Undone: only mixer unplug fixed.

sys/dev/sound/pcm/mixer.c

@@ -774,25 +774,14 @@ mixer_uninit(device_t dev)
 
 	d = device_get_softc(dev);
 	pdev = mixer_get_devt(dev);
-	if (d == NULL || pdev == NULL || pdev->si_drv1 == NULL)
+	if (d == NULL || pdev == NULL || (m = pdev->si_drv1) == NULL)
 		return EBADF;
 
-	m = pdev->si_drv1;
 	KASSERT(m != NULL, ("NULL snd_mixer"));
 	KASSERT(m->type == MIXER_TYPE_PRIMARY,
 	    ("%s(): illegal mixer type=%d", __func__, m->type));
 
-	snd_mtxlock(m->lock);
-
-	if (m->busy) {
-		snd_mtxunlock(m->lock);
-		return EBUSY;
-	}
-
-	/* destroy dev can sleep --hps */
-
-	snd_mtxunlock(m->lock);
-
+	d->mixer_dev = NULL;
 	pdev->si_drv1 = NULL;
 	destroy_dev(pdev);
 
@@ -812,7 +801,6 @@ mixer_uninit(device_t dev)
 	snd_mtxfree(m->lock);
 	kobj_delete((kobj_t)m, M_MIXER);
 
-	d->mixer_dev = NULL;
 
 	--mixer_count;
 

sys/dev/sound/pcm/sound.c

@@ -1145,9 +1145,7 @@ pcm_unregister(device_t dev)
 {
 	struct snddev_info *d;
 	struct pcm_channel *ch;
-	struct thread *td;
 
-	td = curthread;
 	d = device_get_softc(dev);
 
 	if (!PCM_ALIVE(d)) {
@@ -1194,15 +1192,7 @@ pcm_unregister(device_t dev)
 		}
 	}
 
-	if (mixer_uninit(dev) == EBUSY) {
-		device_printf(dev, "unregister: mixer busy\n");
-		PCM_LOCK(d);
-		if (d->clones != NULL)
-			(void)snd_clone_enable(d->clones);
-		PCM_RELEASE(d);
-		PCM_UNLOCK(d);
-		return (EBUSY);
-	}
+	mixer_uninit(dev);
 
 	/* remove /dev/sndstat entry first */
 	sndstat_unregister(dev);

sys/dev/sound/usb/uaudio.c

@@ -1235,8 +1235,10 @@ uaudio_detach_sub(device_t dev)
 	if (sc->sc_child[i].pcm_registered) {
 		error = pcm_unregister(dev);
 	} else {
-		if (sc->sc_child[i].mixer_init)
-			error = mixer_uninit(dev);
+		if (sc->sc_child[i].mixer_init) {
+			error = 0;
+			mixer_uninit(dev);
+		}
 	}
 
 	if (error) {