ALSA: hda: Avoid racy recreation of widget kobjects

The refresh of HD-audio widget sysfs kobjects via
snd_hdac_refresh_widget_sysfs() is slightly racy.
The driver recreates the whole tree from scratch after deleting the
whole.  When CONFIG_DEBUG_KOBJECT_RELEASE option is used, kobject
release doesn't happen immediately but delayed, while the re-creation
of the same named kobject happens soon after invoking kobject_put().
This may end up with the conflicts of duplicated kobjects, as found in
the bug report below.

In this patch, we take another approach to refresh the tree: instead
of recreating the whole tree, just add the new nodes and delete the
non-existing nodes.  Since the refresh happens only once at
initialization, no longer race would happen.

Along with the code change, merge snd_hdac_refresh_widget_sysfs() with
the existing snd_hdac_refresh_widgets() with an additional bool flag
for simplifying the code.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=197307
Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/hdaudio.h

@@ -111,8 +111,7 @@ void snd_hdac_device_unregister(struct hdac_device *codec);
 int snd_hdac_device_set_chip_name(struct hdac_device *codec, const char *name);
 int snd_hdac_codec_modalias(struct hdac_device *hdac, char *buf, size_t size);
 
-int snd_hdac_refresh_widgets(struct hdac_device *codec);
-int snd_hdac_refresh_widget_sysfs(struct hdac_device *codec);
+int snd_hdac_refresh_widgets(struct hdac_device *codec, bool sysfs);
 
 unsigned int snd_hdac_make_cmd(struct hdac_device *codec, hda_nid_t nid,
 			       unsigned int verb, unsigned int parm);

sound/hda/hdac_device.c

@@ -87,7 +87,7 @@ int snd_hdac_device_init(struct hdac_device *codec, struct hdac_bus *bus,
 
 	fg = codec->afg ? codec->afg : codec->mfg;
 
-	err = snd_hdac_refresh_widgets(codec);
+	err = snd_hdac_refresh_widgets(codec, false);
 	if (err < 0)
 		goto error;
 
@@ -388,11 +388,12 @@ static void setup_fg_nodes(struct hdac_device *codec)
 /**
  * snd_hdac_refresh_widgets - Reset the widget start/end nodes
  * @codec: the codec object
+ * @sysfs: re-initialize sysfs tree, too
  */
-int snd_hdac_refresh_widgets(struct hdac_device *codec)
+int snd_hdac_refresh_widgets(struct hdac_device *codec, bool sysfs)
 {
 	hda_nid_t start_nid;
-	int nums;
+	int nums, err;
 
 	nums = snd_hdac_get_sub_nodes(codec, codec->afg, &start_nid);
 	if (!start_nid || nums <= 0 || nums >= 0xff) {
@@ -401,6 +402,12 @@ int snd_hdac_refresh_widgets(struct hdac_device *codec)
 		return -EINVAL;
 	}
 
+	if (sysfs) {
+		err = hda_widget_sysfs_reinit(codec, start_nid, nums);
+		if (err < 0)
+			return err;
+	}
+
 	codec->num_nodes = nums;
 	codec->start_nid = start_nid;
 	codec->end_nid = start_nid + nums;
@@ -408,36 +415,6 @@ int snd_hdac_refresh_widgets(struct hdac_device *codec)
 }
 EXPORT_SYMBOL_GPL(snd_hdac_refresh_widgets);
 
-/**
- * snd_hdac_refresh_widget_sysfs - Reset the codec widgets and reinit the
- * codec sysfs
- * @codec: the codec object
- *
- * first we need to remove sysfs, then refresh widgets and lastly
- * recreate it
- */
-int snd_hdac_refresh_widget_sysfs(struct hdac_device *codec)
-{
-	int ret;
-
-	if (device_is_registered(&codec->dev))
-		hda_widget_sysfs_exit(codec);
-	ret = snd_hdac_refresh_widgets(codec);
-	if (ret) {
-		dev_err(&codec->dev, "failed to refresh widget: %d\n", ret);
-		return ret;
-	}
-	if (device_is_registered(&codec->dev)) {
-		ret = hda_widget_sysfs_init(codec);
-		if (ret) {
-			dev_err(&codec->dev, "failed to init sysfs: %d\n", ret);
-			return ret;
-		}
-	}
-	return ret;
-}
-EXPORT_SYMBOL_GPL(snd_hdac_refresh_widget_sysfs);
-
 /* return CONNLIST_LEN parameter of the given widget */
 static unsigned int get_num_conns(struct hdac_device *codec, hda_nid_t nid)
 {

sound/hda/hdac_sysfs.c

@@ -414,3 +414,50 @@ void hda_widget_sysfs_exit(struct hdac_device *codec)
 {
 	widget_tree_free(codec);
 }
+
+int hda_widget_sysfs_reinit(struct hdac_device *codec,
+			    hda_nid_t start_nid, int num_nodes)
+{
+	struct hdac_widget_tree *tree;
+	hda_nid_t end_nid = start_nid + num_nodes;
+	hda_nid_t nid;
+	int i;
+
+	if (!codec->widgets)
+		return hda_widget_sysfs_init(codec);
+
+	tree = kmemdup(codec->widgets, sizeof(*tree), GFP_KERNEL);
+	if (!tree)
+		return -ENOMEM;
+
+	tree->nodes = kcalloc(num_nodes + 1, sizeof(*tree->nodes), GFP_KERNEL);
+	if (!tree->nodes) {
+		kfree(tree);
+		return -ENOMEM;
+	}
+
+	/* prune non-existing nodes */
+	for (i = 0, nid = codec->start_nid; i < codec->num_nodes; i++, nid++) {
+		if (nid < start_nid || nid >= end_nid)
+			free_widget_node(codec->widgets->nodes[i],
+					 &widget_node_group);
+	}
+
+	/* add new nodes */
+	for (i = 0, nid = start_nid; i < num_nodes; i++, nid++) {
+		if (nid < codec->start_nid || nid >= codec->end_nid)
+			add_widget_node(tree->root, nid, &widget_node_group,
+					&tree->nodes[i]);
+		else
+			tree->nodes[i] =
+				codec->widgets->nodes[nid - codec->start_nid];
+	}
+
+	/* replace with the new tree */
+	kfree(codec->widgets->nodes);
+	kfree(codec->widgets);
+	codec->widgets = tree;
+
+	kobject_uevent(tree->root, KOBJ_CHANGE);
+	return 0;
+}

sound/hda/local.h

@@ -28,6 +28,8 @@ static inline unsigned int get_wcaps_channels(u32 wcaps)
 
 extern const struct attribute_group *hdac_dev_attr_groups[];
 int hda_widget_sysfs_init(struct hdac_device *codec);
+int hda_widget_sysfs_reinit(struct hdac_device *codec, hda_nid_t start_nid,
+			    int num_nodes);
 void hda_widget_sysfs_exit(struct hdac_device *codec);
 
 #endif /* __HDAC_LOCAL_H */

sound/pci/hda/hda_codec.c

@@ -977,7 +977,7 @@ int snd_hda_codec_update_widgets(struct hda_codec *codec)
 	hda_nid_t fg;
 	int err;
 
-	err = snd_hdac_refresh_widget_sysfs(&codec->core);
+	err = snd_hdac_refresh_widgets(&codec->core, true);
 	if (err < 0)
 		return err;