From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759260Ab2DZWR7 (ORCPT ); Thu, 26 Apr 2012 18:17:59 -0400 Received: from mail-pz0-f51.google.com ([209.85.210.51]:48607 "EHLO mail-pz0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754520Ab2DZWR6 (ORCPT ); Thu, 26 Apr 2012 18:17:58 -0400 Date: Thu, 26 Apr 2012 15:17:53 -0700 From: Tejun Heo To: Alan Stern Cc: "Eric W. Biederman" , Peter Zijlstra , Kernel development list Subject: Re: Lockdep false positive in sysfs Message-ID: <20120426221753.GF27486@google.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 26, 2012 at 02:14:30PM -0400, Alan Stern wrote: > > > Hmmm.... This happens because, by default, sysfs_dirents for the same > > > attr share the same lockdep key. This happens from > > > sysfs_dirent_init_lockdep(). Hmm.... we can, > > > > > > * Somehow assign different keys to sysfs_dirents for the specific > > > attr. Use array of attrs indexed by bus depth? > > > > Possible with sysfs_attr_init but pretty ugly. Especially since it > > sounds like this is a situation that does not presuppose a maximum > > depth. I do remember that the lockdep keys must be statically allocated > > which makes this a challenge. The depth is limited by USB spec. > I agree; this doesn't seem like a good approach. It sure isn't pretty but probably best matches the situation in the sense that lockdep would actually be able to know about the nesting going on. > Another idea is to have A's method temporarily drop the sysfs readlock. > Of course that would put the onus on the USB core of guaranteeing that > A cannot be removed while this happens, but we can handle that. Yeah, that's an easier way out. Please make it a proper sysfs API call tho so that people working on sysfs later can know of the special case. Thanks. -- tejun