linux-kernel - [PATCH v4 05/15] software_node: Enforce parent before child ordering of nodes arrays

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Message-Id: <20210103231235.792999-6-djrscally@gmail.com>
Date:   Sun,  3 Jan 2021 23:12:25 +0000
From:   Daniel Scally <djrscally@...il.com>
To:     linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-media@...r.kernel.org, devel@...ica.org,
        gregkh@...uxfoundation.org, rjw@...ysocki.net,
        sergey.senozhatsky@...il.com, mchehab@...nel.org
Cc:     lenb@...nel.org, yong.zhi@...el.com, sakari.ailus@...ux.intel.com,
        bingbu.cao@...el.com, tian.shu.qiu@...el.com,
        robert.moore@...el.com, erik.kaneda@...el.com, pmladek@...e.com,
        rostedt@...dmis.org, andriy.shevchenko@...ux.intel.com,
        linux@...musvillemoes.dk,
        laurent.pinchart+renesas@...asonboard.com,
        jacopo+renesas@...ndi.org, kieran.bingham+renesas@...asonboard.com,
        hverkuil-cisco@...all.nl, m.felsch@...gutronix.de,
        niklas.soderlund+renesas@...natech.se, slongerbeam@...il.com,
        heikki.krogerus@...ux.intel.com, linus.walleij@...aro.org,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: [PATCH v4 05/15] software_node: Enforce parent before child ordering of nodes arrays

Registering software_nodes with the .parent member set to point to a
currently unregistered software_node has the potential for problems,
so enforce parent -> child ordering in arrays passed in to
software_node_register_nodes().

Software nodes that are children of another software node should be
unregistered before their parent. To allow easy unregistering of an array
of software_nodes ordered parent to child, reverse the order in which
software_node_unregister_nodes() unregisters software_nodes.

Suggested-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Signed-off-by: Daniel Scally <djrscally@...il.com>
---
Changes in v4:

	- None

 drivers/base/swnode.c | 42 ++++++++++++++++++++++++++++++------------
 1 file changed, 30 insertions(+), 12 deletions(-)

diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
index 615a0c93e116..ade49173ff8d 100644
--- a/drivers/base/swnode.c
+++ b/drivers/base/swnode.c
@@ -692,7 +692,11 @@ swnode_register(const struct software_node *node, struct swnode *parent,
  * software_node_register_nodes - Register an array of software nodes
  * @nodes: Zero terminated array of software nodes to be registered
  *
- * Register multiple software nodes at once.
+ * Register multiple software nodes at once. If any node in the array
+ * has its .parent pointer set (which can only be to another software_node),
+ * then its parent **must** have been registered before it is; either outside
+ * of this function or by ordering the array such that parent comes before
+ * child.
  */
 int software_node_register_nodes(const struct software_node *nodes)
 {
@@ -700,14 +704,23 @@ int software_node_register_nodes(const struct software_node *nodes)
 	int i;
 
 	for (i = 0; nodes[i].name; i++) {
-		ret = software_node_register(&nodes[i]);
-		if (ret) {
-			software_node_unregister_nodes(nodes);
-			return ret;
+		const struct software_node *parent = nodes[i].parent;
+
+		if (parent && !software_node_to_swnode(parent)) {
+			ret = -EINVAL;
+			goto err_unregister_nodes;
 		}
+
+		ret = software_node_register(&nodes[i]);
+		if (ret)
+			goto err_unregister_nodes;
 	}
 
 	return 0;
+
+err_unregister_nodes:
+	software_node_unregister_nodes(nodes);
+	return ret;
 }
 EXPORT_SYMBOL_GPL(software_node_register_nodes);
 
@@ -715,18 +728,23 @@ EXPORT_SYMBOL_GPL(software_node_register_nodes);
  * software_node_unregister_nodes - Unregister an array of software nodes
  * @nodes: Zero terminated array of software nodes to be unregistered
  *
- * Unregister multiple software nodes at once.
+ * Unregister multiple software nodes at once. If parent pointers are set up
+ * in any of the software nodes then the array **must** be ordered such that
+ * parents come before their children.
  *
- * NOTE: Be careful using this call if the nodes had parent pointers set up in
- * them before registering.  If so, it is wiser to remove the nodes
- * individually, in the correct order (child before parent) instead of relying
- * on the sequential order of the list of nodes in the array.
+ * NOTE: If you are uncertain whether the array is ordered such that
+ * parents will be unregistered before their children, it is wiser to
+ * remove the nodes individually, in the correct order (child before
+ * parent).
  */
 void software_node_unregister_nodes(const struct software_node *nodes)
 {
-	int i;
+	unsigned int i = 0;
+
+	while (nodes[i].name)
+		i++;
 
-	for (i = 0; nodes[i].name; i++)
+	while (i--)
 		software_node_unregister(&nodes[i]);
 }
 EXPORT_SYMBOL_GPL(software_node_unregister_nodes);
-- 
2.25.1