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=-5.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_PASS,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 7F1BEC43219 for ; Wed, 1 May 2019 21:56:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 496892089E for ; Wed, 1 May 2019 21:56:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=tobin.cc header.i=@tobin.cc header.b="EzNYLkd3"; dkim=pass (2048-bit key) header.d=messagingengine.com header.i=@messagingengine.com header.b="IvaHd04W" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726283AbfEAV45 (ORCPT ); Wed, 1 May 2019 17:56:57 -0400 Received: from wout1-smtp.messagingengine.com ([64.147.123.24]:59501 "EHLO wout1-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726137AbfEAV44 (ORCPT ); Wed, 1 May 2019 17:56:56 -0400 Received: from compute5.internal (compute5.nyi.internal [10.202.2.45]) by mailout.west.internal (Postfix) with ESMTP id 3CC0B514; Wed, 1 May 2019 17:56:55 -0400 (EDT) Received: from mailfrontend1 ([10.202.2.162]) by compute5.internal (MEProxy); Wed, 01 May 2019 17:56:55 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=tobin.cc; h=date :from:to:cc:subject:message-id:references:mime-version :content-type:in-reply-to; s=fm3; bh=KSx46+0od7zYFYf4TPD9PRc6aSB MI50hqnUo753dPAU=; b=EzNYLkd3Xb9BP3/F0v5TphBf8Dr3N6A4VlM3iEPdNKp HrDjoG1KOSAM+mew12aPwDx3y9ya5D5+SsIQJMfKsYGsXS+FH/S8wSw59xWRMeLQ MHJtNDezeA3bdNiHsJFnzJIetdHOTbSeEjp7ZaSZ4ewQQIAnuZoP6aVCNvW2kTlH Qy+vplVDVV0EUc/2ROwhWAZwyMQjteTaQOvEibyIhH5nnfcxIGBMKWqwLQKIO7jL 8MU1N4fHXGAB0hOR6+7t34jmwmQSaS1q3sTBOnsbeV8Fmc9Kx01XGtuysvLubxKR +UvQXLYZQ5c3xVcFU+ZMmnPQjyjCTQA4jpQWvn3iX6A== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to:x-me-proxy :x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s=fm2; bh=KSx46+ 0od7zYFYf4TPD9PRc6aSBMI50hqnUo753dPAU=; b=IvaHd04WVJMG3do4XQFHU/ /tWqjB3Otq0Lw6Dyqa4AeKIGbc/Iq8Ce0vlZ4/RinRKdhcxfPgCh3T2U/g6Nkix9 AHEQddkWMxCahaBGmoykmv6eGZ3hYOpGsnZ0CiWRXE55PSEo0fMEypRCyfRYlj25 uWm5Wl8MuZTPLf6JrsUuHZg/AVLuH391As2oxWtfoefCylpQV6x6mQhYY5yeTLWX woS7zk8snHXpSN4/KI1IYyuq4t3ZDk6+9khv0H6ZyT4e6+u7hOZGIGZsJt5RGAtm AWYaBG1ooLzpK+wCT84JapKt4rEn1VbUfyri1rAduyepCBXZ8vnahBdtM5LlqBeA == X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeduuddrieejgdduieelucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne gfrhhlucfvnfffucdlfedtmdenucfjughrpeffhffvuffkfhggtggujgfofgesthdtredt ofervdenucfhrhhomhepfdfvohgsihhnucevrdcujfgrrhguihhnghdfuceomhgvsehtoh gsihhnrdgttgeqnecukfhppeduvddurdeggedrvddtgedrvdefheenucfrrghrrghmpehm rghilhhfrhhomhepmhgvsehtohgsihhnrdgttgenucevlhhushhtvghrufhiiigvpedt X-ME-Proxy: Received: from localhost (ppp121-44-204-235.bras1.syd2.internode.on.net [121.44.204.235]) by mail.messagingengine.com (Postfix) with ESMTPA id E5C6DE4382; Wed, 1 May 2019 17:56:52 -0400 (EDT) Date: Thu, 2 May 2019 07:56:16 +1000 From: "Tobin C. Harding" To: Greg Kroah-Hartman 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: <20190501215616.GD18827@eros.localdomain> References: <20190427081330.GA26788@eros.localdomain> <20190427192809.GA8454@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190427192809.GA8454@kroah.com> X-Mailer: Mutt 1.11.4 (2019-03-13) 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 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. Thanks for taking the time to explain this stuff. thanks Tobin. Leaving below for reference. > Now if kobject_init_and_add() had failed, and called kobject_put() right > away, that would have freed the larger "struct foo", but not cleaned up > the reference to the baz pointer. > > Yes, you can move all of the other destruction logic into the release > function, to then get rid of baz, but that really doesn't work in the > real world as there are times you want to drop that when you "know" you > can drop it, not when the last reference goes away as those are > different lifecycles. > > Same thing goes for 'struct device'. It too is a kobject, so think > about if the driver core's call to initialize the kobject failed, would > it be ok at that exact moment in time to free everything? > > Look at the "joy" that is device_add(). If kobject_add() fails, we have > to clean up the glue directory that we had created, _before_ we can then > call put_device(). Then stack another layer on top of that, look at > usb_new_device(). If the call to device_add() fails, it needs to do > some housekeeping before it can drop the last reference to the device to > free the memory up.