ALSA: seq: Correct unlock sequence at snd_seq_client_ioctl_unlock()

The doubly unlock sequence at snd_seq_client_ioctl_unlock() is tricky.
I took a direct unref call since I thought it would avoid
misunderstanding, but rather this seems more confusing.  Let's use
snd_seq_client_unlock() consistently even if they look strange to be
called twice, and add more comments for avoiding reader's confusion.

Fixes: 6b580f52 ("ALSA: seq: Protect racy pool manipulation from OSS sequencer")
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/seq/seq_clientmgr.c

@@ -191,6 +191,7 @@ bool snd_seq_client_ioctl_lock(int clientid)
 	if (!client)
 		return false;
 	mutex_lock(&client->ioctl_mutex);
+	/* The client isn't unrefed here; see snd_seq_client_ioctl_unlock() */
 	return true;
 }
 EXPORT_SYMBOL_GPL(snd_seq_client_ioctl_lock);
@@ -204,7 +205,11 @@ void snd_seq_client_ioctl_unlock(int clientid)
 	if (WARN_ON(!client))
 		return;
 	mutex_unlock(&client->ioctl_mutex);
-	snd_use_lock_free(&client->use_lock);
+	/* The doubly unrefs below are intentional; the first one releases the
+	 * leftover from snd_seq_client_ioctl_lock() above, and the second one
+	 * is for releasing snd_seq_client_use_ptr() in this function
+	 */
+	snd_seq_client_unlock(client);
 	snd_seq_client_unlock(client);
 }
 EXPORT_SYMBOL_GPL(snd_seq_client_ioctl_unlock);