Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750904AbaAEGFh (ORCPT ); Sun, 5 Jan 2014 01:05:37 -0500 Received: from mail-pb0-f48.google.com ([209.85.160.48]:41945 "EHLO mail-pb0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750747AbaAEGFf (ORCPT ); Sun, 5 Jan 2014 01:05:35 -0500 Date: Sat, 4 Jan 2014 22:05:31 -0800 From: Dmitry Torokhov To: Greg Kroah-Hartman Cc: Mikulas Patocka , Jeff Mahoney , torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com, tglx@linutronix.de, paulmck@linux.vnet.ibm.com, mingo@kernel.org Subject: Re: [PATCH] kobject: provide kobject_put_wait to fix module unload race Message-ID: <20140105060531.GD18213@core.coreip.homeip.net> References: <20140104181620.GA2087@kroah.com> <20140105034228.GC22595@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140105034228.GC22595@kroah.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1912 Lines: 44 On Sat, Jan 04, 2014 at 07:42:28PM -0800, Greg Kroah-Hartman wrote: > On Sat, Jan 04, 2014 at 03:35:39PM -0500, Mikulas Patocka wrote: > > > > > > On Sat, 4 Jan 2014, Greg Kroah-Hartman wrote: > > > > > On Sat, Jan 04, 2014 at 01:06:01PM -0500, Mikulas Patocka wrote: > > > > Hi > > > > > > > > I noticed that Jeff Mahoney added a new structure kobj_completion, defined > > > > in include/linux/kobj_completion.h to the kernel 3.13-rc1 in the patch > > > > eee031649707db3c9920d9498f8d03819b74fc23. In the current upstream kernel, > > > > this interface is still unused. > > > > > > There are pending btrfs patches to use this interface. > > > > > > > However, converting the drivers to use kobj_completion is not trivial > > > > (note that all users of the original kobject interface are buggy - so all > > > > of them need to be converted). > > > > > > Wait, what? How are "all users" buggy? Please explain this in detail. > > > > 1) some code takes a reference to a kobject > > 2) the user unloads the device > > 3) the device driver unload routine calls kobject_put (but there is still > > reference, so the kobject is not destroyed) > > A driver should never be messing around with "raw" kobjects, they should > be using a 'struct device' which is created/managed by the subsystem > they belong to. See Dmitry's example of input and serio as ways to do > this, also USB and PCI do this properly. Well, Mikulas is correct in the sense that there is still a race between release function invoking the final module_put() and getting preempted and module getting unloaded by another thread. Hitting this race is pretty hard though. -- Dmitry -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/