ALSA: hda: ext: fix locking in stream_release

The snd_hdac_ext_stream_release() routine uses the bus reg_lock, but
releases it before calling snd_hdac_stream_release() where the bus
reg_lock is taken again.

This creates a timing window where the link stream release could test
an invalid 'opened' boolean status and fail to recouple the host and
link parts.

Fix by exposing a locked version of snd_hdac_stream_release() and use
it without releasing the spinlock.

Signed-off-by: Pierre-Louis Bossart <[e-mail]>
Reviewed-by: Bard Liao <[e-mail]>
Reviewed-by: Péter Ujfalusi <[e-mail]>
Reviewed-by: Kai Vehmanen <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Takashi Iwai <[e-mail]>

include/sound/hdaudio.h

···
 			  int idx, int direction, int tag);
 struct hdac_stream *snd_hdac_stream_assign(struct hdac_bus *bus,
 					   struct snd_pcm_substream *substream);
+void snd_hdac_stream_release_locked(struct hdac_stream *azx_dev);
 void snd_hdac_stream_release(struct hdac_stream *azx_dev);
 struct hdac_stream *snd_hdac_get_stream(struct hdac_bus *bus,
 					int dir, int stream_tag);

sound/hda/ext/hdac_ext_stream.c

···
 		spin_lock_irq(&bus->reg_lock);
 		if (hext_stream->decoupled && !hext_stream->link_locked)
 			snd_hdac_ext_stream_decouple_locked(bus, hext_stream, false);
+		snd_hdac_stream_release_locked(&hext_stream->hstream);
 		spin_unlock_irq(&bus->reg_lock);
-		snd_hdac_stream_release(&hext_stream->hstream);
 		break;
 
 	case HDAC_EXT_STREAM_TYPE_LINK:

sound/hda/hdac_stream.c

···
 EXPORT_SYMBOL_GPL(snd_hdac_stream_assign);
 
 /**
+ * snd_hdac_stream_release_locked - release the assigned stream
+ * @azx_dev: HD-audio core stream to release
+ *
+ * Release the stream that has been assigned by snd_hdac_stream_assign().
+ * The bus->reg_lock needs to be taken at a higher level
+ */
+void snd_hdac_stream_release_locked(struct hdac_stream *azx_dev)
+{
+	azx_dev->opened = 0;
+	azx_dev->running = 0;
+	azx_dev->substream = NULL;
+}
+EXPORT_SYMBOL_GPL(snd_hdac_stream_release_locked);
+
+/**
  * snd_hdac_stream_release - release the assigned stream
  * @azx_dev: HD-audio core stream to release
  *
···
 	struct hdac_bus *bus = azx_dev->bus;
 
 	spin_lock_irq(&bus->reg_lock);
-	azx_dev->opened = 0;
-	azx_dev->running = 0;
-	azx_dev->substream = NULL;
+	snd_hdac_stream_release_locked(azx_dev);
 	spin_unlock_irq(&bus->reg_lock);
 }
 EXPORT_SYMBOL_GPL(snd_hdac_stream_release);