From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS, T_DKIMWL_WL_HIGH,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6BDDCC43219 for ; Thu, 2 May 2019 07:28:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 27AF520873 for ; Thu, 2 May 2019 07:28:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556782095; bh=DC0FQv9GFtu+ZYqXRgLOg+n4FU6hMP8NXEIF454sXOI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=oiUoJuMwzToR9ekPLcaMS5yiE7q4I+Rfa3HIhv+s1LesuvgCWTfMNw3zuVzoDoRSh qElzrZpMGzbukQc9EaJRi90QCHuny2UmKqwfAce+JPJnlfgaiMsr5PbygM2QeGoJVe Nx+TcFGTO669t31yr+GCt8JyoU7sJB6FGhLtlAQo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726244AbfEBH2N (ORCPT ); Thu, 2 May 2019 03:28:13 -0400 Received: from mail.kernel.org ([198.145.29.99]:45928 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726055AbfEBH2N (ORCPT ); Thu, 2 May 2019 03:28:13 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1910A2081C; Thu, 2 May 2019 07:28:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556782091; bh=DC0FQv9GFtu+ZYqXRgLOg+n4FU6hMP8NXEIF454sXOI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=vcmHFz58Axgdg8hr2j0BxK9XxjCz9myXjH39Ghb2m35tSG/FvLpsJdRQknnVL6y5P yE5/arwXVq3y0KNC9WP/iPMchGlJ7rAkQNMcZ14k9Vt2bISmU3/OARZ9yAfUjab7xc C/uWL5+SqIf3LIf2Wbb/gUmK3Qb9oFZIGiNqbJ5o= Date: Thu, 2 May 2019 09:28:08 +0200 From: Greg Kroah-Hartman To: "Tobin C. Harding" Cc: "Rafael J. Wysocki" , cl@linux.com, tycho@tycho.ws, willy@infradead.org, linux-kernel@vger.kernel.org Subject: Re: memleak around kobject_init_and_add() Message-ID: <20190502072808.GA14064@kroah.com> References: <20190427081330.GA26788@eros.localdomain> <20190427192809.GA8454@kroah.com> <20190501215616.GD18827@eros.localdomain> <20190502071742.GC16247@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190502071742.GC16247@kroah.com> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 02, 2019 at 09:17:42AM +0200, Greg Kroah-Hartman wrote: > On Thu, May 02, 2019 at 07:56:16AM +1000, Tobin C. Harding wrote: > > On Sat, Apr 27, 2019 at 09:28:09PM +0200, Greg Kroah-Hartman wrote: > > > On Sat, Apr 27, 2019 at 06:13:30PM +1000, Tobin C. Harding wrote: > > > > (Note at bottom on reasons for 'To' list 'Cc' list) > > > > > > > > Hi, > > > > > > > > kobject_init_and_add() seems to be routinely misused. A failed call to this > > > > function requires a call to kobject_put() otherwise we leak memory. > > > > > > > > Examples memleaks can be seen in: > > > > > > > > mm/slub.c > > > > fs/btrfs/sysfs.c > > > > fs/xfs/xfs_sysfs.h: xfs_sysfs_init() > > > > > > > > Question: Do we fix the misuse or fix the API? > > > > > > Fix the misuse. > > > > > > > $ git grep kobject_init_and_add | wc -l > > > > 117 > > > > > > > > Either way, we will have to go through all 117 call sites and check them. > > > > > > Yes. Same for other functions like device_add(), that is the "pattern" > > > those users must follow. > > > > > > > I > > > > don't mind fixing them all but I don't want to do it twice because I chose the > > > > wrong option. Reaching out to those more experienced for a suggestion please. > > > > > > > > Fix the API > > > > ----------- > > > > > > > > Typically init functions do not require cleanup if they fail, this argument > > > > leads to this patch > > > > > > > > diff --git a/lib/kobject.c b/lib/kobject.c > > > > index aa89edcd2b63..62328054bbd0 100644 > > > > --- a/lib/kobject.c > > > > +++ b/lib/kobject.c > > > > @@ -453,6 +453,9 @@ int kobject_init_and_add(struct kobject *kobj, struct kobj_type *ktype, > > > > retval = kobject_add_varg(kobj, parent, fmt, args); > > > > va_end(args); > > > > > > > > + if (retval) > > > > + kobject_put(kobj); > > > > + > > > > return retval; > > > > } > > > > EXPORT_SYMBOL_GPL(kobject_init_and_add); > > > > > > I would _love_ to do this, but realize what a kobject really is. > > > > > > It's just a "base object" that is embedded inside of some other object. > > > The kobject core has no idea what is going on outside of itself. If the > > > kobject_init_and_add() function fails, it can NOT drop the last > > > reference on itself, as that would cause the memory owned by the _WHOLE_ > > > structure the kobject is embedded in, to be freed. > > > > > > And the kobject core can not "know" that something else needed to be > > > done _before_ that memory could be freed. What if the larger structure > > > needs to have some other destructor called on it first? What if > > > some other api initialization needs to be torn down. > > > > > > As an example, consider this code: > > > > > > struct foo { > > > struct kobject kobj; > > > struct baz *baz; > > > }; > > > > > > void foo_release(struct kobject *kobj) > > > { > > > struct foo *foo = container_of(kobj, struct foo, kobj); > > > kfree(foo); > > > } > > > > > > struct kobj_type foo_ktype = { > > > .release = foo_release, > > > }; > > > > > > struct foo *foo_create(struct foo *parent, char *name) > > > { > > > struct *foo; > > > > > > foo = kzalloc(sizeof(*foo), GFP_KERNEL); > > > if (!foo) > > > return NULL; > > > > > > foo->baz = baz_create(name); > > > if (!foo->baz) > > > return NULL; > > > > > > ret = kobject_init_and_add(&foo->kobj, foo_ktype, &parent->kobj, "foo-%s", name); > > > if (ret) { > > > baz_destroy(foo->baz); > > > kobject_put(&foo->kobj); > > > return NULL; > > > } > > > > > > return foo; > > > } > > > > > > void foo_destroy(struct foo *foo) > > > { > > > baz_destroy(foo->baz); > > > kobject_del(&foo->kobj); > > kojbect_put(&foo->kobj); > > > } > > > > Does this need this extra call to kobject_put()? Then foo_create() > > leaves foo with a refcount of 1 and foo_destroy drops that refcount. > > Oops, no, I messed this up, it should _only_ be a call to > kobject_put(), kobject_del() is not needed here. > > kobject_del() is for people who "really want to control the lifetime" of > a kobject. All it does is remove the kobject from sysfs, and drop the > parent reference of the kobject, allowing the kobject to be "free" on > it's own. Later a kobject_put() call must be called on it to really > clean it up. > > If you just call kobject_put(), and this is the last reference, > kobject_del() will be correctly called for you by the kobject code, as > it "knows" this is time to clean up the sysfs entities. > > A "normal" user should never have to call kobject_del(). Which means your other patch about the kerneldoc for that function is also not correct, I'll go fix that up now... thanks, greg k-h