From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755288AbdDNWbq (ORCPT ); Fri, 14 Apr 2017 18:31:46 -0400 Received: from bombadil.infradead.org ([65.50.211.133]:34039 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751371AbdDNWbo (ORCPT ); Fri, 14 Apr 2017 18:31:44 -0400 Date: Fri, 14 Apr 2017 15:31:38 -0700 From: "Darren Hart (VMware)" To: Thomas Gleixner Cc: LKML , Ingo Molnar , Peter Zijlstra Subject: [PATCH] futex: Clarify mark_wake_futex memory barrier usage Message-ID: <20170414223138.GA4222@fury> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.7.1 (2016-10-04) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Clarify the scenario described in mark_wake_futex requiring the smp_store_release(). Update the comment to explicitly refer to the plist_del now under __unqueue_futex() (previously plist_del was in the same function as the comment). Signed-off-by: Darren Hart (VMware) Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Peter Zijlstra --- kernel/futex.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index ede2f1e..357348a 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1380,10 +1380,11 @@ static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q) wake_q_add(wake_q, p); __unqueue_futex(q); /* - * The waiting task can free the futex_q as soon as - * q->lock_ptr = NULL is written, without taking any locks. A - * memory barrier is required here to prevent the following - * store to lock_ptr from getting ahead of the plist_del. + * The waiting task can free the futex_q as soon as q->lock_ptr = NULL + * is written, without taking any locks. This is possible in the event + * of a spurious wakeup, for example. A memory barrier is required here + * to prevent the following store to lock_ptr from getting ahead of the + * plist_del in __unqueue_futex(). */ smp_store_release(&q->lock_ptr, NULL); } -- 2.9.3 -- Darren Hart VMware Open Source Technology Center