From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964951Ab2LFXCN (ORCPT ); Thu, 6 Dec 2012 18:02:13 -0500 Received: from mail-la0-f46.google.com ([209.85.215.46]:36894 "EHLO mail-la0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753563Ab2LFXCM (ORCPT ); Thu, 6 Dec 2012 18:02:12 -0500 MIME-Version: 1.0 In-Reply-To: References: <1354210800-27230-1-git-send-email-dinggnu@gmail.com> <20121130001304.GB2590@local> Date: Fri, 7 Dec 2012 00:02:11 +0100 X-Google-Sender-Auth: vn7VGxa5-05JINtY_eeVHxMqkmk Message-ID: Subject: Re: [PATCH v2 1/1] uio.c: solve memory leak From: Cong Ding To: "Hans J. Koch" Cc: Greg Kroah-Hartman , linux-kernel@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ping Hans, did you have any comment on this? - cong On Fri, Nov 30, 2012 at 12:03 PM, Cong Ding wrote: > Hi Hans, I think the memory allocated with kzalloc is properly freed > by calling kobject_put. > > I can give a simple explanation. > > 1) when we call kobject_init, the parameter portio_attr_type is > passed in. portio_attr_type includes a function pointer to > portio_release, which releases the memory of portio. > > 2) when we call kobject_put, kref_put is called with the pointer of > function kobject_release. > 3) kref_put calls kref_sub, with the same pointer of function kobject_release. > 4) and kref_put calls the function kboject_release if > atomic_sub_and_test returns true > > 5) let's look at what kobject_release is. it calls kobject_cleanup, > and kobject_cleanup calls t->release(kobj) where t->release is exactly > the function we passed in through portio_init at step (1). so function > portio_release is called, and the memory allocated with kzalloc is > freed. > > If there are anything wrong in my analysis, please feel free to let me know. > > Personally, I suggest to add a function to create and release > uio_portio, which is similar as kobject_create and kobject_put in file > lib/kobject.c. In this way, it avoid other readers thinking the memory > is not freed (and we should add some comments here). For example, > uio_portio_create call kzalloc and kboject_init, and returns > uio_portio, which is similar as function kobject_create; and > uio_portio_release calls kobject_put to release the memory. And we do > same thing for uio_map. > > The usage here is quite strange, but it works. If I write this > function from zero, I will use a pointer to kobject in uio_portio > struct instead of kobject struct itself. In this case I can call > kobject_create instead of kobject_init, and then we do both > kzalloc(uio_portio) and kfree(uio_portio) in the file uio.c. > > Best, > Cong > > On Fri, Nov 30, 2012 at 1:13 AM, Hans J. Koch wrote: >> There's still another bug: The memory allocated with kzalloc is >> never freed.