From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932071AbcCBPmZ (ORCPT ); Wed, 2 Mar 2016 10:42:25 -0500 Received: from mail.kernel.org ([198.145.29.136]:58238 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752046AbcCBPhS (ORCPT ); Wed, 2 Mar 2016 10:37:18 -0500 Message-Id: <20160302153714.251074185@goodmis.org> User-Agent: quilt/0.61-1 Date: Wed, 02 Mar 2016 10:36:59 -0500 From: Steven Rostedt To: linux-kernel@vger.kernel.org, linux-rt-users Cc: Thomas Gleixner , Carsten Emde , Sebastian Andrzej Siewior , John Kacur , Paul Gortmaker Subject: [PATCH RT 01/20] sched: reset tasks lockless wake-queues on fork() References: <20160302153658.995489487@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Disposition: inline; filename=0001-sched-reset-task-s-lockless-wake-queues-on-fork.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.18.27-rt27-rc1 stable review patch. If anyone has any objections, please let me know. ------------------ From: Sebastian Andrzej Siewior In 7675104990ed ("sched: Implement lockless wake-queues") we gained lockless wake-queues. -RT managed to lockup itself with those. There could be multiple attempts for task X to enqueue it for a wakeup _even_ if task X is already running. The reason is that task X could be runnable but not yet on CPU. The the task performing the wakeup did not leave the CPU it could performe multiple wakeups. With the proper timming task X could be running and enqueued for a wakeup. If this happens while X is performing a fork() then its its child will have a !NULL `wake_q` member copied. This is not a problem as long as the child task does not participate in lockless wakeups :) Fixes: 7675104990ed ("sched: Implement lockless wake-queues") Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Steven Rostedt --- kernel/fork.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/fork.c b/kernel/fork.c index 3a8ecfb38831..1c4edaf4ec36 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -364,6 +364,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig) #endif tsk->splice_pipe = NULL; tsk->task_frag.page = NULL; + tsk->wake_q.next = NULL; account_kernel_stack(ti, 1); -- 2.7.0