From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932215AbcIEICC (ORCPT ); Mon, 5 Sep 2016 04:02:02 -0400 Received: from metis.ext.4.pengutronix.de ([92.198.50.35]:51763 "EHLO metis.ext.4.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751031AbcIEICA (ORCPT ); Mon, 5 Sep 2016 04:02:00 -0400 Message-ID: <1473062516.2456.25.camel@pengutronix.de> Subject: Re: [PATCH] drm/imx: Fix of_node ref counting From: Philipp Zabel To: Christophe JAILLET Cc: airlied@linux.ie, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org Date: Mon, 05 Sep 2016 10:01:56 +0200 In-Reply-To: <1472971523-4143-1-git-send-email-christophe.jaillet@wanadoo.fr> References: <1472971523-4143-1-git-send-email-christophe.jaillet@wanadoo.fr> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.9-1+b1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 2001:67c:670:100:96de:80ff:fec2:9969 X-SA-Exim-Mail-From: p.zabel@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Christophe, Am Sonntag, den 04.09.2016, 08:45 +0200 schrieb Christophe JAILLET: > This code is spurious. > It takes a ref on a node, then call 'of_node_put' on it and then store > this node somewhere. The node pointer is not stored. Note that np is not dereferenced at all, we just compare the pointer value against dev->of_node. It doesn't matter whether we drop the reference before or after that. > It is likely that taking the ref on the parent node and releasing the child > node was expected instead. Initially, np is assigned to the void *data parameter. The caller holds the reference to that, and we are not allowed to decrement its refcount (as of_get_next_parent does). Otherwise the iterator calling this match function would drop references of all the device_nodes it compares against. > So, use 'of_get_next_parent' instead. It does all this in just one > function call. > > Signed-off-by: Christophe JAILLET > --- > Un-tested > --- > drivers/gpu/drm/imx/imx-drm-core.c | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/imx/imx-drm-core.c b/drivers/gpu/drm/imx/imx-drm-core.c > index 438bac8fbc2b..60fb388c80f8 100644 > --- a/drivers/gpu/drm/imx/imx-drm-core.c > +++ b/drivers/gpu/drm/imx/imx-drm-core.c > @@ -449,10 +449,8 @@ static int compare_of(struct device *dev, void *data) > } > > /* Special case for LDB, one device for two channels */ > - if (of_node_cmp(np->name, "lvds-channel") == 0) { > - np = of_get_parent(np); > - of_node_put(np); > - } This could have been written as: bool match; /* Special case for LDB, one device for two channels */ if (of_node_cmp(np->name, "lvds-channel") == 0) { struct device_node *parent = of_get_parent(np); match = dev->of_node == parent; of_node_put(parent); } else { match = dev->of_node == np; } return match; which does exactly the same. Maybe the reuse of np and the pointer comparison after of_node_put warrants a comment. > + if (of_node_cmp(np->name, "lvds-channel") == 0) > + np = of_get_next_parent(np); > > return dev->of_node == np; > } thanks Philipp