From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753692AbbH0M1b (ORCPT ); Thu, 27 Aug 2015 08:27:31 -0400 Received: from mail-wi0-f172.google.com ([209.85.212.172]:36343 "EHLO mail-wi0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751979AbbH0M1a (ORCPT ); Thu, 27 Aug 2015 08:27:30 -0400 Date: Thu, 27 Aug 2015 14:27:27 +0200 From: Michal Hocko To: LKML Cc: Oleg Nesterov , Peter Zijlstra , David Howells , Linus Torvalds Subject: wake_up_process implied memory barrier clarification Message-ID: <20150827122727.GC27052@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, I have just stumbled over the comment above wake_up_process which claims: " * It may be assumed that this function implies a write memory barrier before * changing the task state if and only if any tasks are woken up. " but try_to_wake_up does smp_mb__before_spinlock and did smp_wmb since 04e2f1741d235 unconditionally. The comment was added when the smp_wmb was in place already so I am wondering whether the comment is wrong/misleading. Could somebody clarify please? -- Michal Hocko SUSE Labs