From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757095AbcEDDgX (ORCPT ); Tue, 3 May 2016 23:36:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40299 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756746AbcEDDgW (ORCPT ); Tue, 3 May 2016 23:36:22 -0400 Date: Tue, 3 May 2016 22:36:19 -0500 From: Josh Poimboeuf To: Jiri Kosina Cc: Miroslav Benes , jeyu@redhat.com, pmladek@suse.com, jslaby@suse.cz, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org, huawei.libin@huawei.com, minfei.huang@yahoo.com Subject: Re: [RFC PATCH] livepatch: allow removal of a disabled patch Message-ID: <20160504033619.5osteklgal3ixcbo@treble> References: <1462190242-24731-1-git-send-email-mbenes@suse.cz> <20160503213709.g66xr624pwn7oguu@treble> <20160504023948.ttb3ko2wnicwruwy@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20160504023948.ttb3ko2wnicwruwy@treble> User-Agent: Mutt/1.6.0.1 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 03, 2016 at 09:39:48PM -0500, Josh Poimboeuf wrote: > On Wed, May 04, 2016 at 12:31:12AM +0200, Jiri Kosina wrote: > > On Tue, 3 May 2016, Josh Poimboeuf wrote: > > > > > > 1. Do we really need a completion? If I am not missing something > > > > kobject_del() always waits for sysfs callers to leave thanks to kernfs > > > > active protection. > > > > > > What do you mean by "kernfs active protection"? I see that > > > kernfs_remove() gets the kernfs_mutex lock, but I can't find anywhere > > > that a write to a sysfs file uses that lock. > > > > > > I'm probably missing something... > > > > I don't want to speak on Miroslav's behalf, but I'm pretty sure that what > > he has on mind is per-kernfs_node active refcounting kernfs does (see > > kernfs_node->active, and especially it's usage in __kernfs_remove()). > > > > More specifically, execution of store() and show() sysfs callbacks is > > guaranteed (by kernfs) to happen with that particular attribute's active > > reference held for reading (and that makes it impossible for that > > attribute to vanish prematurely). > > Thanks, that makes sense. > > So what exactly is the problem the completion is trying to solve? Is it > to ensure that the kobject has been cleaned up before it returns to the > caller, in case the user wants to call klp_register() again after > unregistering? > > If so, that's quite an unusual use case which I think we should just > consider unsupported. In fact, if you try to do it, kobject_init() > complains loudly because kobj->state_initialized is still 1 because > kobjects aren't meant to be reused like that. ... and now I realize the point is actually to prevent the caller from freeing klp_patch before kobject_cleanup() runs. So yeah, it looks like we need the completion in case CONFIG_DEBUG_KOBJECT_RELEASE is enabled. Or alternatively we could convert patch->kobj to be dynamically allocated instead of embedded in klp_patch. -- Josh