From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754287AbeDZUUr (ORCPT ); Thu, 26 Apr 2018 16:20:47 -0400 Received: from mail-pf0-f193.google.com ([209.85.192.193]:39972 "EHLO mail-pf0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752358AbeDZUUp (ORCPT ); Thu, 26 Apr 2018 16:20:45 -0400 X-Google-Smtp-Source: AIpwx4/MDZ4jeMSDg5LIEgCeoLKjjovTl313lxokvVxjrCrbtdujVt0CDephgDcl+DSmYAzVnfps1A== Subject: Re: [PATCH v2] of: overlay: Stop leaking resources on overlay removal To: Jan Kiszka , Pantelis Antoniou , Rob Herring , devicetree Cc: Linux Kernel Mailing List , Alan Tull , Geert Uytterhoeven References: From: Frank Rowand Message-ID: Date: Thu, 26 Apr 2018 13:20:43 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > --- > 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