From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760718AbZE3NIH (ORCPT ); Sat, 30 May 2009 09:08:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757956AbZE3NHz (ORCPT ); Sat, 30 May 2009 09:07:55 -0400 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 To: Tejun Heo 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" References: <1243551665-23596-4-git-send-email-ebiederm@xmission.com> <4A1FA777.3040200@kernel.org> <4A210DEF.2030203@kernel.org> From: ebiederm@xmission.com (Eric W. Biederman) Date: Sat, 30 May 2009 06:07:47 -0700 In-Reply-To: <4A210DEF.2030203@kernel.org> (Tejun Heo's message of "Sat\, 30 May 2009 19\:43\:59 +0900") Message-ID: User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-XM-SPF: eid=;;;mid=;;;hst=in01.mta.xmission.com;;;ip=76.21.114.89;;;frm=ebiederm@xmission.com;;;spf=neutral X-SA-Exim-Connect-IP: 76.21.114.89 X-SA-Exim-Rcpt-To: tj@kernel.org, ebiederm@aristanetworks.com, greg@kroah.com, kay.sievers@vrfy.org, linux-fsdevel@vger.kernel.org, cornelia.huck@de.ibm.com, linux-kernel@vger.kernel.org, gregkh@suse.de, akpm@linux-foundation.org X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-DCC: XMission; sa01 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Tejun Heo X-Spam-Relay-Country: X-Spam-Report: * -1.8 ALL_TRUSTED Passed through trusted hosts only via SMTP * 1.5 XMNoVowels Alpha-numberic number with no vowels * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -2.6 BAYES_00 BODY: Bayesian spam probability is 0 to 1% * [score: 0.0000] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa01 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 T_TooManySym_01 4+ unique symbols in subject * 0.1 XMSolicitRefs_0 Weightloss drug * 0.0 XM_SPF_Neutral SPF-Neutral * 0.4 UNTRUSTED_Relay Comes from a non-trusted relay Subject: Re: [PATCH 04/24] sysfs: Normalize removing sysfs directories. X-SA-Exim-Version: 4.2.1 (built Thu, 25 Oct 2007 00:26:12 +0000) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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