Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755038AbaJ1X3w (ORCPT ); Tue, 28 Oct 2014 19:29:52 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:54929 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754790AbaJ1X3t (ORCPT ); Tue, 28 Oct 2014 19:29:49 -0400 Date: Tue, 28 Oct 2014 16:25:57 -0700 From: "Paul E. McKenney" To: Al Viro Cc: Miklos Szeredi , Linus Torvalds , Linux-Fsdevel , Kernel Mailing List , linux-unionfs@vger.kernel.org Subject: Re: [GIT PULL] overlay filesystem v25 Message-ID: <20141028232557.GF5718@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20141025081845.GJ7996@ZenIV.linux.org.uk> <20141025170609.GK7996@ZenIV.linux.org.uk> <20141027155901.GE5718@linux.vnet.ibm.com> <20141027172800.GW7996@ZenIV.linux.org.uk> <20141027173621.GG5718@linux.vnet.ibm.com> <20141028011214.GZ7996@ZenIV.linux.org.uk> <20141028041127.GM5718@linux.vnet.ibm.com> <20141028225512.GD7996@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141028225512.GD7996@ZenIV.linux.org.uk> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14102823-0029-0000-0000-000000F53D54 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 28, 2014 at 10:55:13PM +0000, Al Viro wrote: > On Mon, Oct 27, 2014 at 09:11:27PM -0700, Paul E. McKenney wrote: > > On Tue, Oct 28, 2014 at 01:12:14AM +0000, Al Viro wrote: > > > On Mon, Oct 27, 2014 at 10:36:21AM -0700, Paul E. McKenney wrote: > > > > Code making direct use of smp_read_barrier_depends() is harder to read, > > > > in my experience, but good point on the sparse noise. Maybe a new > > > > lockless_dereference() primitive? Maybe something like the following? > > > > (Untested, probably does not even build.) > > > > > > > > #define lockless_dereference(p) \ > > > > ({ \ > > > > typeof(*p) *_________p1 = ACCESS_ONCE(p); \ > > > > smp_read_barrier_depends(); /* Dependency order vs. p above. */ \ > > > > _________p1; \ > > > > }) > > > > > > Hmm... Where would you prefer to put it? rcupdate.h? > > > > Good a place as any, I guess. Please see patch below. Left to myself, > > I would send this along for the next merge window, but please let me > > know if you would like it sooner. > > It's needed sooner, unfortunately. Guys, could you take a look at > vfs.git#for-linus and comment? The version in your tree looks good. I will drop my commit in favor of yours. The use of lockless_dereference() and smp_mb__before_spinlock() in d45f00ae43 (overlayfs: barriers for opening upper-layer directory) looks fine to me. Only nit is lack of space between "=" and lockless_dereference(). Thanx, Paul -- 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/