From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1423924AbcFMS4o (ORCPT ); Mon, 13 Jun 2016 14:56:44 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:44237 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1423152AbcFMS4e (ORCPT ); Mon, 13 Jun 2016 14:56:34 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, bigeasy@linutronix.de, "Peter Zijlstra" , "Davidlohr Bueso" , "Thomas Gleixner" , dvhart@infradead.org, "Davidlohr Bueso" Date: Mon, 13 Jun 2016 19:36:37 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 035/114] futex: Acknowledge a new waiter in counter before plist In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8011:400e:2:6f00:88c8:c921:d332 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.36-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Davidlohr Bueso commit fe1bce9e2107ba3a8faffe572483b6974201a0e6 upstream. Otherwise an incoming waker on the dest hash bucket can miss the waiter adding itself to the plist during the lockless check optimization (small window but still the correct way of doing this); similarly to the decrement counterpart. Suggested-by: Peter Zijlstra Signed-off-by: Davidlohr Bueso Cc: Davidlohr Bueso Cc: bigeasy@linutronix.de Cc: dvhart@infradead.org Link: http://lkml.kernel.org/r/1461208164-29150-1-git-send-email-dave@stgolabs.net Signed-off-by: Thomas Gleixner Signed-off-by: Ben Hutchings --- kernel/futex.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1398,8 +1398,8 @@ void requeue_futex(struct futex_q *q, st if (likely(&hb1->chain != &hb2->chain)) { plist_del(&q->list, &hb1->chain); hb_waiters_dec(hb1); - plist_add(&q->list, &hb2->chain); hb_waiters_inc(hb2); + plist_add(&q->list, &hb2->chain); q->lock_ptr = &hb2->lock; } get_futex_key_refs(key2);