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>

1 files changed, 47 insertions, 0 deletions

diff --git a/sound/hda/hdac_sysfs.c b/sound/hda/hdac_sysfs.c
index 42d61bf41969..e123ba6b2e81 100644
--- a/sound/hda/hdac_sysfs.c
+++ b/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;
+}