From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751811AbWLNANK (ORCPT ); Wed, 13 Dec 2006 19:13:10 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751813AbWLNANK (ORCPT ); Wed, 13 Dec 2006 19:13:10 -0500 Received: from mx1.suse.de ([195.135.220.2]:35094 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751811AbWLNANJ (ORCPT ); Wed, 13 Dec 2006 19:13:09 -0500 Date: Wed, 13 Dec 2006 16:12:46 -0800 From: Greg KH To: Venkatesh Pallipadi Cc: Andrew Morton , Arjan , linux-kernel Subject: Re: kref refcnt and false positives Message-ID: <20061214001246.GA10056@suse.de> References: <20061213153408.A13049@unix-os.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20061213153408.A13049@unix-os.sc.intel.com> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 13, 2006 at 03:34:08PM -0800, Venkatesh Pallipadi wrote: > > With WARN_ON addition to kobject_init() > [ http://kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.19/2.6.19-mm1/dont-use/broken-out/gregkh-driver-kobject-warn.patch ] > > I started seeing following WARNING on CPU offline followed by online on my > x86_64 system. > > WARNING at lib/kobject.c:172 kobject_init() > > Call Trace: > [] dump_trace+0xaa/0x3ef > [] show_trace+0x3a/0x50 > [] dump_stack+0x15/0x17 > [] kobject_init+0x3f/0x8a > [] kobject_register+0x1a/0x3e > [] sysdev_register+0x5b/0xf9 > [] mce_create_device+0x77/0xf4 > [] mce_cpu_callback+0x3a/0xe5 > [] notifier_call_chain+0x26/0x3b > [] raw_notifier_call_chain+0x9/0xb > [] _cpu_up+0xb4/0xdc > [] cpu_up+0x2b/0x42 > [] store_online+0x4a/0x72 > [] sysdev_store+0x24/0x26 > [] sysfs_write_file+0xcf/0xfc > [] vfs_write+0xae/0x154 > [] sys_write+0x47/0x6f > [] system_call+0x7e/0x83 > DWARF2 unwinder stuck at system_call+0x7e/0x83 > Leftover inexact backtrace: > > This is a false positive as mce.c is unregistering/registering sysfs > interfaces cleanly on hotplug. The warning above tends to look like this is not true. > kref_put() and conditional decrement of refcnt seems to be the root cause > for this and the patch below resolves the issue for me. Why? Are you properly initializing your kref to null before you register it with the driver core? Or is it a static object? > Original comment seemed to indicate that this conditional thing was > performance related. Is it really? If not, we should consider the below patch. Yes, it's a performance gain and I don't see how this patch would change the above warning. thanks, greg k-h