of: overlay: Stop leaking resources on overlay removal

Only the overlay notifier callbacks have a chance to potentially get
hold of references to those two resources, but they are not supposed to
store them beyond OF_OVERLAY_POST_REMOVE.

Document the overlay notifier API, its constraint regarding pointer
lifetime, and then remove intentional leaks of ovcs->overlay_tree and
ovcs->fdt from free_overlay_changeset.

See also https://lkml.org/lkml/2018/4/23/1063 and following.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Frank Rowand <frowand.list@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>

diff --git a/Documentation/devicetree/overlay-notes.txt b/Documentation/devicetree/overlay-notes.txt
index a4feb6dde8cd08e83b7b9672c90f863311dc9d75..725fb8d255c16a8ae722a4c4d47d1492900d724a 100644 (file)
--- a/Documentation/devicetree/overlay-notes.txt
+++ b/Documentation/devicetree/overlay-notes.txt
@@ -98,6 +98,14 @@ Finally, if you need to remove all overlays in one-go, just call
 of_overlay_remove_all() which will remove every single one in the correct
 order.
 
+In addition, there is the option to register notifiers that get called on
+overlay operations. See of_overlay_notifier_register/unregister and
+enum of_overlay_notify_action for details.
+
+Note that a notifier callback is not supposed to store pointers to a device
+tree node or its content beyond OF_OVERLAY_POST_REMOVE corresponding to the
+respective node it received.
+
 Overlay DTS Format
 ------------------
 

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index b35fe88f18514d13eaf9460885f42657bd52ed61..7baa53e5b1d74d469959341945e3bc239cf7d5c7 100644 (file)
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -102,12 +102,28 @@ static DEFINE_IDR(ovcs_idr);
 
 static BLOCKING_NOTIFIER_HEAD(overlay_notify_chain);
 
+/**
+ * of_overlay_notifier_register() - Register notifier for overlay operations
+ * @nb:                Notifier block to register
+ *
+ * Register for notification on overlay operations on device tree nodes. The
+ * reported actions definied by @of_reconfig_change. The notifier callback
+ * furthermore receives a pointer to the affected device tree node.
+ *
+ * Note that a notifier callback is not supposed to store pointers to a device
+ * tree node or its content beyond @OF_OVERLAY_POST_REMOVE corresponding to the
+ * respective node it received.
+ */
 int of_overlay_notifier_register(struct notifier_block *nb)
 {
        return blocking_notifier_chain_register(&overlay_notify_chain, nb);
 }
 EXPORT_SYMBOL_GPL(of_overlay_notifier_register);
 
+/**
+ * of_overlay_notifier_register() - Unregister notifier for overlay operations
+ * @nb:                Notifier block to unregister
+ */
 int of_overlay_notifier_unregister(struct notifier_block *nb)
 {
        return blocking_notifier_chain_unregister(&overlay_notify_chain, nb);
@@ -671,17 +687,13 @@ static void free_overlay_changeset(struct overlay_changeset *ovcs)
                of_node_put(ovcs->fragments[i].overlay);
        }
        kfree(ovcs->fragments);
-
        /*
-        * TODO
-        *
-        * would like to: kfree(ovcs->overlay_tree);
-        * but can not since drivers may have pointers into this data
-        *
-        * would like to: kfree(ovcs->fdt);
-        * but can not since drivers may have pointers into this data
+        * There should be no live pointers into ovcs->overlay_tree and
+        * ovcs->fdt due to the policy that overlay notifiers are not allowed
+        * to retain pointers into the overlay devicetree.
         */
-
+       kfree(ovcs->overlay_tree);
+       kfree(ovcs->fdt);
        kfree(ovcs);
 }