On 04/26/18 04:00, Jan Kiszka wrote: > 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.kis...@siemens.com> > --- > Documentation/devicetree/overlay-notes.txt | 8 ++++++++ > drivers/of/overlay.c | 30 > +++++++++++++++++++++--------- > 2 files changed, 29 insertions(+), 9 deletions(-) > > diff --git a/Documentation/devicetree/overlay-notes.txt > b/Documentation/devicetree/overlay-notes.txt > index a4feb6dde8cd..725fb8d255c1 100644 > --- 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 b35fe88f1851..7baa53e5b1d7 100644 > --- 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); > } > >
These added kfree()s are depending on good review of overlay notifier patches to prevent retaining pointers into this freed memory. When this patch is accepted I will submit a patch to add a "K:" pattern line to the Overlay MAINTAINERS entry to catch when overlay notifiers are added. Reviewed-by: Frank Rowand <frowand.l...@gmail.com>
