Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756516Ab3H3Vak (ORCPT ); Fri, 30 Aug 2013 17:30:40 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:35103 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755569Ab3H3Vai (ORCPT ); Fri, 30 Aug 2013 17:30:38 -0400 Date: Fri, 30 Aug 2013 22:30:30 +0100 From: Al Viro To: Waiman Long Cc: Linus Torvalds , Ingo Molnar , Benjamin Herrenschmidt , Jeff Layton , Miklos Szeredi , Ingo Molnar , Thomas Gleixner , linux-fsdevel , Linux Kernel Mailing List , Peter Zijlstra , Steven Rostedt , Andi Kleen , "Chandramouleeswaran, Aswin" , "Norton, Scott J" Subject: Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount Message-ID: <20130830213029.GG13318@ZenIV.linux.org.uk> References: <52200DAE.2020303@hp.com> <5220E56A.80603@hp.com> <5220F090.5050908@hp.com> <5220FD51.2010709@hp.com> <20130830205404.GF13318@ZenIV.linux.org.uk> <52210A55.8010308@hp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <52210A55.8010308@hp.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1695 Lines: 32 On Fri, Aug 30, 2013 at 05:10:45PM -0400, Waiman Long wrote: > On 08/30/2013 04:54 PM, Al Viro wrote: > >On Fri, Aug 30, 2013 at 01:43:11PM -0700, Linus Torvalds wrote: > >>On Fri, Aug 30, 2013 at 1:15 PM, Waiman Long wrote: > >>>The prepend_path() isn't all due to getcwd. The correct profile should be > >>Ugh. I really think that prepend_path() should just be rewritten to > >>run entirely under RCU. > >> > >>Then we can remove *all* the stupid locking, and replace it with doing ^^^^^^^^^^^^^^^^^^^^^ > >>a read-lock on the rename sequence count, and repeating if requited. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > >> > >>That shouldn't even be hard to do, it just requires mindless massaging > >>and being careful. > >Not really. Sure, you'll retry it if you race with d_move(); that's not > >the real problem - access past the end of the object containing ->d_name.name > >would screw you and that's what ->d_lock is preventing there. Delayed freeing > >of what ->d_name is pointing into is fine, but it's not the only way to get > >hurt there... > > Actually, prepend_path() was called with rename_lock taken. So > d_move() couldn't be run at the same time. Am I right? See above. You are right, but if Linus wants to turn that sucker into reader (which is possible - see e.g. cifs build_path_from_dentry() and its ilk), d_move() races will start to play. -- 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/