of: overlay: add tests to validate kfrees from overlay removal

Add checks:
  - attempted kfree due to refcount reaching zero before overlay
    is removed
  - properties linked to an overlay node when the node is removed
  - node refcount > one during node removal in a changeset destroy,
    if the node was created by the changeset

After applying this patch, several validation warnings will be
reported from the devicetree unittest during boot due to
pre-existing devicetree bugs. The warnings will be similar to:

  OF: ERROR: of_node_release(), unexpected properties in /testcase-data/overlay-node/test-bus/test-unittest11
  OF: ERROR: memory leak, expected refcount 1 instead of 2, of_node_get()/of_node_put() unbalanced - destroy cset entry: attach overlay node /testcase-data-2/substation@100/
  hvac-medium-2
Tested-by: Alan Tull <atull@kernel.org>
Signed-off-by: Frank Rowand <frank.rowand@sony.com>

drivers/of/dynamic.c

@@ -330,6 +330,25 @@ void of_node_release(struct kobject *kobj)
 	if (!of_node_check_flag(node, OF_DYNAMIC))
 		return;
 
+	if (of_node_check_flag(node, OF_OVERLAY)) {
+
+		if (!of_node_check_flag(node, OF_OVERLAY_FREE_CSET)) {
+			/* premature refcount of zero, do not free memory */
+			pr_err("ERROR: memory leak before free overlay changeset,  %pOF\n",
+			       node);
+			return;
+		}
+
+		/*
+		 * If node->properties non-empty then properties were added
+		 * to this node either by different overlay that has not
+		 * yet been removed, or by a non-overlay mechanism.
+		 */
+		if (node->properties)
+			pr_err("ERROR: %s(), unexpected properties in %pOF\n",
+			       __func__, node);
+	}
+
 	property_list_free(node->properties);
 	property_list_free(node->deadprops);
 
@@ -434,6 +453,16 @@ struct device_node *__of_node_dup(const struct device_node *np,
 
 static void __of_changeset_entry_destroy(struct of_changeset_entry *ce)
 {
+	if (ce->action == OF_RECONFIG_ATTACH_NODE &&
+	    of_node_check_flag(ce->np, OF_OVERLAY)) {
+		if (kref_read(&ce->np->kobj.kref) > 1) {
+			pr_err("ERROR: memory leak, expected refcount 1 instead of %d, of_node_get()/of_node_put() unbalanced - destroy cset entry: attach overlay node %pOF\n",
+			       kref_read(&ce->np->kobj.kref), ce->np);
+		} else {
+			of_node_set_flag(ce->np, OF_OVERLAY_FREE_CSET);
+		}
+	}
+
 	of_node_put(ce->np);
 	list_del(&ce->node);
 	kfree(ce);

drivers/of/overlay.c

@@ -373,6 +373,7 @@ static int add_changeset_node(struct overlay_changeset *ovcs,
 			return -ENOMEM;
 
 		tchild->parent = target_node;
+		of_node_set_flag(tchild, OF_OVERLAY);
 
 		ret = of_changeset_attach_node(&ovcs->cset, tchild);
 		if (ret)

include/linux/of.h

@@ -138,11 +138,16 @@ extern struct device_node *of_aliases;
 extern struct device_node *of_stdout;
 extern raw_spinlock_t devtree_lock;
 
-/* flag descriptions (need to be visible even when !CONFIG_OF) */
-#define OF_DYNAMIC	1 /* node and properties were allocated via kmalloc */
-#define OF_DETACHED	2 /* node has been detached from the device tree */
-#define OF_POPULATED	3 /* device already created for the node */
-#define OF_POPULATED_BUS	4 /* of_platform_populate recursed to children of this node */
+/*
+ * struct device_node flag descriptions
+ * (need to be visible even when !CONFIG_OF)
+ */
+#define OF_DYNAMIC		1 /* (and properties) allocated via kmalloc */
+#define OF_DETACHED		2 /* detached from the device tree */
+#define OF_POPULATED		3 /* device already created */
+#define OF_POPULATED_BUS	4 /* platform bus created for children */
+#define OF_OVERLAY		5 /* allocated for an overlay */
+#define OF_OVERLAY_FREE_CSET	6 /* in overlay cset being freed */
 
 #define OF_BAD_ADDR	((u64)-1)