Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757683AbYJHBGS (ORCPT ); Tue, 7 Oct 2008 21:06:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755238AbYJHBGE (ORCPT ); Tue, 7 Oct 2008 21:06:04 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:48783 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753459AbYJHBGC (ORCPT ); Tue, 7 Oct 2008 21:06:02 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Tejun Heo Cc: Al Viro , Benjamin Thery , Greg KH , linux-kernel@vger.kernel.org, "Serge E. Hallyn" , Al Viro , Linus Torvalds References: <48D7AC44.6050208@bull.net> <20080922153455.GA6238@kroah.com> <48D8FC1E.6000601@bull.net> <20081003101331.GH28946@ZenIV.linux.org.uk> <48EB27FE.2090009@kernel.org> <48EB53B8.5020309@kernel.org> <48EBEE0B.6080009@kernel.org> <48EBFCD3.4050809@kernel.org> Date: Tue, 07 Oct 2008 17:58:34 -0700 In-Reply-To: <48EBFCD3.4050809@kernel.org> (Tejun Heo's message of "Wed, 08 Oct 2008 09:20:35 +0900") Message-ID: User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-XM-SPF: eid=;;;mid=;;;hst=mx04.mta.xmission.com;;;ip=24.130.11.59;;;frm=ebiederm@xmission.com;;;spf=neutral X-SA-Exim-Connect-IP: 24.130.11.59 X-SA-Exim-Rcpt-To: too long (recipient list exceeded maximum allowed size of 128 bytes) X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-DCC: XMission; sa03 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 * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -0.2 BAYES_40 BODY: Bayesian spam probability is 20 to 40% * [score: 0.3131] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa03 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 XM_SPF_Neutral SPF-Neutral Subject: Re: sysfs: tagged directories not merged completely yet X-SA-Exim-Version: 4.2.1 (built Thu, 07 Dec 2006 04:40:56 +0000) X-SA-Exim-Scanned: Yes (on mx04.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1258 Lines: 30 Tejun Heo writes: > Hmmm... I'm probably missing something (and being lazy) but how does it > guarantee the validity of the next pointer after dropping the rcu lock? So in next_tid which is essentially what we would be doing. I grab the rcu_lock. Check something to see if the task I have is still on the list, if it is then I know the next is valid until the end of the rcu grace period. Then I follow the next pointer, and grab the lock again. rcu is pain to get right but at least it is localized pain. >> I'm still not certain how we can get the lock ordering so it doesn't >> cause us problems. I will look at revalidation and what the other >> distributed filesystems are doing and see if that might work. If it >> doesn't we need refactor the VFS locking. > > Yeah, if we can make sysfs behave like other distributed filesystems, it > would be great. :-) I don't think we can make it work but I think we need to exhaust that avenue before saying that the VFS has to change. Eric -- 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/