ALSA: aloop: Avoid unexpected timer event callback tasklets

loopback_snd_timer_close_cable() function waits until all
scheduled tasklets are completed, but the timer is closed after that
and can generate more event callbacks, scheduling new tasklets,
that will not be synchronized with cable closing.
Move tasklet_kill() call to be executed after snd_timer_close()
call to avoid such case.

Fixes: 26c5337 ("ALSA: aloop: Support selection of snd_timer instead of jiffies")
Signed-off-by: Andrew Gabbasov <andrew_gabbasov@mentor.com>
Link: https://lore.kernel.org/r/20191122175218.17187-2-andrew_gabbasov@mentor.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/drivers/aloop.c

@@ -302,15 +302,16 @@ static int loopback_snd_timer_close_cable(struct loopback_pcm *dpcm)
 	if (!cable->snd_timer.instance)
 		return 0;
 
-	/* wait till drain tasklet has finished if requested */
-	tasklet_kill(&cable->snd_timer.event_tasklet);
-
 	/* will only be called from free_cable() when other stream was
 	 * already closed. Other stream cannot be reopened as long as
 	 * loopback->cable_lock is locked. Therefore no need to lock
 	 * cable->lock;
 	 */
 	snd_timer_close(cable->snd_timer.instance);
+
+	/* wait till drain tasklet has finished if requested */
+	tasklet_kill(&cable->snd_timer.event_tasklet);
+
 	snd_timer_instance_free(cable->snd_timer.instance);
 	memset(&cable->snd_timer, 0, sizeof(cable->snd_timer));