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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>
This commit is contained in:
Jan Kiszka 2018-04-26 13:00:30 +02:00 committed by Rob Herring
parent 970f04c840
commit 83ef4777f5
2 changed files with 29 additions and 9 deletions
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8
Documentation/devicetree/overlay-notes.txt
View File

@ -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
------------------

30
drivers/of/overlay.c
View File

@ -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);
}