From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [PATCH 04/24] sysfs: Normalize removing sysfs directories. Date: Sat, 30 May 2009 06:07:47 -0700 Message-ID: References: <1243551665-23596-4-git-send-email-ebiederm@xmission.com> <4A1FA777.3040200@kernel.org> <4A210DEF.2030203@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andrew Morton , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, Cornelia Huck , linux-fsdevel@vger.kernel.org, Kay Sievers , Greg KH , "Eric W. Biederman" To: Tejun Heo Return-path: Received: from out01.mta.xmission.com ([166.70.13.231]:53373 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757873AbZE3NHy (ORCPT ); Sat, 30 May 2009 09:07:54 -0400 In-Reply-To: <4A210DEF.2030203@kernel.org> (Tejun Heo's message of "Sat\, 30 May 2009 19\:43\:59 +0900") Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Tejun Heo writes: > Eric W. Biederman wrote: >> Also, I'm quite uncomfortable with these things >>> being done in non-atomic manner. It can be made to work but things >>> like this can lead to subtle race conditions and with the kind of >>> layering we put on top of sysfs (kobject, driver model, driver >>> midlayers and so on), it isn't all that easy to verify what's going >>> on, so NACK for this one. >> >> Total nonsense. >> >> Mucking about with sysfs after we start deleting a directory is a bug. >> At worst my change makes a buggy race slightly less deterministic. >> >> I am not ready to consider keeping the current unnecessary atomic >> removal step. That unnecessary atomicity makes the following patches >> more difficult, and requires a lot of unnecessary retesting. >> >> What do you think the extra unnecessary atomicity helps protect? > > It's just not a clean API. When people are trying to code things way > up in the stack, they aren't likely to look up the code to see what > assumptions are being made especially when the stack is deep and > complex and sysfs is near the bottom of the tall stack. IMHO > implementing the usually expected semantics at this depth is worth > every effort. It's just good implementation style which might look > like wasted effort but will harden the stack in the long run. Plus, > it's not like making it atomic is difficult or anything. I guess we are going to have to disagree on this one. My take is simply that a correct user has to wait until no one else can find the kobject before calling kobject_del. At which point races are impossible, and it doesn't matter if sysfs_mutex is held across the entire operation. For the long term I still intend to kill __sysfs_remove_dir. Just not in this patch series. Eric