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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C74C0C433FE for ; Thu, 16 Dec 2021 14:14:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230295AbhLPOOo (ORCPT ); Thu, 16 Dec 2021 09:14:44 -0500 Received: from smtp-out2.suse.de ([195.135.220.29]:42854 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229525AbhLPOOn (ORCPT ); Thu, 16 Dec 2021 09:14:43 -0500 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id CF34F1F465; Thu, 16 Dec 2021 14:14:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1639664081; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=1ue6/TYI0i0J8w8ZHXna6f2slYijkGXx+ie8ci2x8po=; b=iG3tZzfJ5SCS+SfJADwn/EPifM89UCPJzH8u6lWyVnQgjHeg04JRxwOrDZypH1wu79x7j3 tPIkYtw9Zdr/UofWIVhlE9NYxGgK0ODkYeu5WAgN4W1aZ0T9hD3k7w4nx36EMfEYt7wS26 1NXLjXTzPZy7tUpR6rEwdDS1iOq5v7E= Received: from suse.cz (unknown [10.100.224.162]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 8377DA3B81; Thu, 16 Dec 2021 14:14:41 +0000 (UTC) Date: Thu, 16 Dec 2021 15:14:38 +0100 From: Petr Mladek To: Greg Kroah-Hartman Cc: David Vernet , Miroslav Benes , linux-doc@vger.kernel.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org, jpoimboe@redhat.com, jikos@kernel.org, joe.lawrence@redhat.com, corbet@lwn.net, yhs@fb.com, songliubraving@fb.com Subject: Re: [PATCH] livepatch: Fix leak on klp_init_patch_early failure path Message-ID: References: <20211213191734.3238783-1-void@manifault.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 2021-12-15 16:35:24, Greg Kroah-Hartman wrote: > On Wed, Dec 15, 2021 at 09:19:59AM +0100, Petr Mladek wrote: > > On Tue 2021-12-14 16:50:15, Greg Kroah-Hartman wrote: > > > > > > kobject_init() does allocate things internally, where does it say it > > > does not? What is trying to be "fixed" here? > > > > Could you please show where things are allocated in kobject_init()? > > I do not see it in the code! > > > > It looks to me like a cargo cult claim to me. > > Hm, I thought I saw it yesterday when I reviewed the code. Let me look > again... > > > Documentation/core-api/kobject.rst says: > > > > Once you registered your kobject via kobject_add(), you must never use > > kfree() to free it directly. The only safe way is to use kobject_put(). > > > > kobject_add() makes perfect sense because it copies the name, takes > > reference to the parent, etc. > > > > kobject_init() just initializes the structure members and nothing else. > > Now it does. In the past, I think we did create some memory. I know > when we hook debugobjects up to kobjects (there's an external patch for > that floating around somewhere), that is one reason to keep the > kobject_put() rule, and there might have been other reasons in the past > 20+ years as well. > > So yes, while you are correct today, the "normal" reference counted > object model patern is "after the object is initialized, it MUST only be > freed by handling its reference count." So let's stick to that rule for > now. Good point. > If you want, I can put some code in the kobject_init() logic to force > this to be the case if it bothers you :) I actually know about one case where this might be very useful. There is the problem with kobject lifetime and module removal. module is removed after mod->exit() callback finishes. But some kobject release() callbacks might be delayed, especillay when CONFIG_DEBUG_KOBJECT_RELEASE is enabled. I have proposed there a solution where kobject_add_internal() takes reference on the module. It would make sure that the module will stay in the memory until the release callbacks is called, see https://lore.kernel.org/all/Ya84O2%2FnYCyNb%2Ffp@alley/ But kobject_add_internal() is not the right place. The reference on the module should be taken already in kobject_init() because the release callbacks might be used after this point. Best Regards, Petr