From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755115Ab3LPRS6 (ORCPT ); Mon, 16 Dec 2013 12:18:58 -0500 Received: from mail-ea0-f173.google.com ([209.85.215.173]:65058 "EHLO mail-ea0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754581Ab3LPRS4 (ORCPT ); Mon, 16 Dec 2013 12:18:56 -0500 Message-ID: <52AF35FD.8000904@linux.com> Date: Mon, 16 Dec 2013 18:18:53 +0100 From: Levente Kurusa Reply-To: Levente Kurusa User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0 MIME-Version: 1.0 To: Greg Kroah-Hartman CC: Bjorn Helgaas , LKML Subject: Re: [PATCH 0/4] treewide: add missing put_device calls References: <1386962557-8899-1-git-send-email-levex@linux.com> <20131214172419.GC22520@kroah.com> <52AD606F.50408@linux.com> <20131215170325.GA28799@kroah.com> In-Reply-To: <20131215170325.GA28799@kroah.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/15/2013 06:03 PM, Greg Kroah-Hartman wrote: > On Sun, Dec 15, 2013 at 08:55:27AM +0100, Levente Kurusa wrote: >> On 12/14/2013 06:24 PM, Greg Kroah-Hartman wrote: >>> On Fri, Dec 13, 2013 at 01:42:05PM -0700, Bjorn Helgaas wrote: >>>> [+cc Greg] >>>> >>>> On Fri, Dec 13, 2013 at 12:22 PM, Levente Kurusa wrote: >>>>> Hi, >>>>> >>>>> This is just the beginning of patchset-set that aims to fix possible >>>>> problems caused by not calling put_device() if device_register() fails. >>>>> >>>>> The root cause for the need to call put_device() is that the underlying >>>>> kobject still has a reference count of 1. Thus, device.release() will not >>>>> be called and the device will just sit there waiting for a put_device(). >>>>> Adding the put_device() also removes the need for the call to kfree() as most >>>>> release functions already call kfree() on the container of the device. >>>>> >>>>> While these have not been experienced, they are potential issues and thus >>>>> they need to be fixed. Also, they are a few more files that have the same >>>>> kind of issue, those will be fixed if these are accepted. >>>> >>>> Thanks for doing this. This is the sort of mistake that just gets >>>> copied everywhere, so fixing the examples in the tree will help >>>> prevent the problem from spreading more. >>>> >>>> I don't know if there's really value in having device_register() >>>> return an error but rely on the caller to do the put_device(). Are >>>> there cases where the caller still needs the struct device even if >>>> device_register() fails? E.g., could we do something like this >>>> instead (I know some callers would also require corresponding changes >>>> to avoid double puts): >> >> There are cases where it is needed. There are quite a few files which >> when device_register() fails, the driver print an error messages. > > That shouldn't be needed, and can be removed. Yes, we could put a pr_warn() when device_register() fails. > >> IIRC, there are also a few where the device is also unregistered from >> the specific subsystem's core. > > Do you have a specific example of this? This should happen in the > release function of the device already, not in some other code. > Character drivers who register with device_register() call cdev_del() when device_register() fails. cdev_del() in turn calls kobject_put on the kobject of the device. Of course, this could also be replaced. Anyways, I have another set of these patches (approx 40) that I will post in a day or so. With that most (if not all) should be fixed. -- Regards, Levente Kurusa