From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753517AbbIAQid (ORCPT ); Tue, 1 Sep 2015 12:38:33 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:48044 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751631AbbIAQic (ORCPT ); Tue, 1 Sep 2015 12:38:32 -0400 Date: Tue, 1 Sep 2015 18:38:12 +0200 From: Peter Zijlstra To: Davidlohr Bueso Cc: Thomas Gleixner , Linus Torvalds , Oleg Nesterov , Paul McKenney , Ingo Molnar , mtk.manpages@gmail.com, dvhart@infradead.org, Vineet.Gupta1@synopsys.com, ralf@linux-mips.org, ddaney@caviumnetworks.com, Will Deacon , linux-kernel@vger.kernel.org Subject: Re: futex atomic vs ordering constraints Message-ID: <20150901163812.GN16853@twins.programming.kicks-ass.net> References: <20150826181659.GW16853@twins.programming.kicks-ass.net> <1440811986.1831.9.camel@stgolabs.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1440811986.1831.9.camel@stgolabs.net> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 28, 2015 at 06:33:06PM -0700, Davidlohr Bueso wrote: > On Wed, 2015-08-26 at 20:16 +0200, Peter Zijlstra wrote: > > Of course, if anything else prior to futex_atomic_op_inuser() implies an > > (RCsc) RELEASE or stronger the primitive can do without providing > > anything itself. > > > > This turns out to be the case, a successful get_futex_key() implies a > > full memory barrier; recent: 1d0dcb3ad9d3 ("futex: Implement lockless > > wakeups"). > > Hmm while it is certainly true that get_futex_key() implies a full > barrier, I don't see why you're referring to the recent wake_q stuff; D'oh, because I'm a sheep or so. I meant: b0c29f79ecea (futexes: Avoid taking the hb->lock if there's nothing to wake up)