From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751459AbbLURRS (ORCPT ); Mon, 21 Dec 2015 12:17:18 -0500 Received: from www.linutronix.de ([62.245.132.108]:50204 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751208AbbLURRR (ORCPT ); Mon, 21 Dec 2015 12:17:17 -0500 Date: Mon, 21 Dec 2015 18:17:10 +0100 From: Sebastian Andrzej Siewior To: Peter Zijlstra Cc: Davidlohr Bueso , Thomas Gleixner , Steven Rostedt , linux-kernel@vger.kernel.org, Ingo Molnar Subject: [PATCH] sched: reset task's lockless wake-queues on fork() Message-ID: <20151221171710.GA5499@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- kernel/fork.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/fork.c b/kernel/fork.c index b508f757c60b..46c1e8342ad8 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -393,6 +393,7 @@ 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); -- 2.6.4