ASoC: SOF: Protect swidget->use_count with mutex for kcontrol access race

The use_count of the swidget is protect by ALSA core PCM locking with the
exception when an associated kcontrol is changed.

It has been observed that a rightly timed kcontrol access during stream
stop can result of an attempt to send a control update to a widget which
has been freed up between the check of the use_count and the message
sending.

We need to protect the entire sof_widget_setup() and sof_widget_free()
execution to make it safe to rely on the use_count.
Move the code under an _unlocked() function and use a mutex to protect
the execution of the functions for concurrency.
On the control path we need to use the lock only for the kcontrol access,
the widget_kcontrol_setup() op is called with the lock already held.

Reported-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Link: https://lore.kernel.org/r/20230127120031.10709-18-peter.ujfalusi@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 10 insertions, 1 deletions

diff --git a/sound/soc/sof/sof-audio.h b/sound/soc/sof/sof-audio.h
index f1bbd1adc8b6..b0593b46d477 100644
--- a/sound/soc/sof/sof-audio.h
+++ b/sound/soc/sof/sof-audio.h
@@ -387,7 +387,16 @@ struct snd_sof_widget {
 	 * up in the DSP.
 	 */
 	bool prepared;
-	int use_count; /* use_count will be protected by the PCM mutex held by the core */
+
+	struct mutex setup_mutex; /* to protect the swidget setup and free operations */
+
+	/*
+	 * use_count is protected by the PCM mutex held by the core and the
+	 * setup_mutex against non stream domain races (kcontrol access for
+	 * example)
+	 */
+	int use_count;
+
 	int core;
 	int id; /* id is the DAPM widget type */
 	/*