From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755544AbbBCBMh (ORCPT ); Mon, 2 Feb 2015 20:12:37 -0500 Received: from ozlabs.org ([103.22.144.67]:51876 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755258AbbBCBMe (ORCPT ); Mon, 2 Feb 2015 20:12:34 -0500 Message-ID: <1422925952.4625.3.camel@ellerman.id.au> Subject: Re: [1/3] powerpc/pmac: Fix DT refcount imbalance in pmac_pic_probe_oldstyle From: Michael Ellerman To: Geert Uytterhoeven Cc: Geert Uytterhoeven , Benjamin Herrenschmidt , Bryan Wu , Richard Purdie , Jingoo Han , Lee Jones , "devicetree@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "linux-kernel@vger.kernel.org" Date: Tue, 03 Feb 2015 12:12:32 +1100 In-Reply-To: References: <1421243519-6257-2-git-send-email-geert+renesas@glider.be> <20150130040904.8F89D1402A7@ozlabs.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.7-0ubuntu1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2015-01-30 at 10:00 +0100, Geert Uytterhoeven wrote: > Hi Michael, > > On Fri, Jan 30, 2015 at 5:09 AM, Michael Ellerman wrote: > > On Wed, 2015-14-01 at 13:51:57 UTC, Geert Uytterhoeven wrote: > >> of_find_node_by_name() calls of_node_put() on its "from" parameter, > >> which must not be done on "master", as it's still in use, and will be > >> released manually later. This may cause a zero kref refcount. > >> Use of_get_child_by_name() instead to fix this. > > > > But of_find_node_by_name() searches *all* nodes, not just the children of the > > parameter. > > That's correct. However, I guess the second mac-io will just be a direct child. Yeah OK, I don't have a system or an example device tree to check. > > So this is a logic change AFAICS, and I have no idea what machines we'd need to > > test on to check it. > > Originally it comes from arch/ppc/platforms/pmac_pic.c, added in 2002 in > full-history-linux commit 5ea3254844ae344a > ("Import arch/ppc and include/asm-ppc changes from linuxppc_2_5 tree"). > > I've also checked my linuxppc mail archives from 1997-2002, but couldn't find > the actual patch and a description. > > So I don't know on which machines it's needed. Yep. Ben or Paul might know, but even then their memory may not be perfect :) > > So I think an of_node_get(master) would be safer and also fix the refcounting. > > If no one can confirm the above, that may indeed be the best solution. I think so. Given how few of these machines are around it's easy to break them with an inadvertent change like this, so I think it's better to be safe. Wanna send a patch for that? cheers