From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752552AbcAFStT (ORCPT ); Wed, 6 Jan 2016 13:49:19 -0500 Received: from terminus.zytor.com ([198.137.202.10]:54649 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751954AbcAFStQ (ORCPT ); Wed, 6 Jan 2016 13:49:16 -0500 Date: Wed, 6 Jan 2016 10:48:37 -0800 From: tip-bot for Sebastian Andrzej Siewior Message-ID: Cc: mingo@kernel.org, rostedt@goodmis.org, linux-kernel@vger.kernel.org, dbueso@suse.de, bigeasy@linutronix.de, peterz@infradead.org, tglx@linutronix.de, torvalds@linux-foundation.org, hpa@zytor.com Reply-To: bigeasy@linutronix.de, peterz@infradead.org, linux-kernel@vger.kernel.org, dbueso@suse.de, rostedt@goodmis.org, mingo@kernel.org, hpa@zytor.com, torvalds@linux-foundation.org, tglx@linutronix.de In-Reply-To: <20151221171710.GA5499@linutronix.de> References: <20151221171710.GA5499@linutronix.de> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/core] sched/core: Reset task' s lockless wake-queues on fork() Git-Commit-ID: 093e5840ae76f1082633503964d035f40ed0216d X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 093e5840ae76f1082633503964d035f40ed0216d Gitweb: http://git.kernel.org/tip/093e5840ae76f1082633503964d035f40ed0216d Author: Sebastian Andrzej Siewior AuthorDate: Mon, 21 Dec 2015 18:17:10 +0100 Committer: Ingo Molnar CommitDate: Wed, 6 Jan 2016 11:01:07 +0100 sched/core: Reset task's lockless wake-queues on fork() In the following commit: 7675104990ed ("sched: Implement lockless wake-queues") we gained lockless wake-queues. The -RT kernel 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 :) Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Peter Zijlstra (Intel) Cc: Davidlohr Bueso Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Fixes: 7675104990ed ("sched: Implement lockless wake-queues") Link: http://lkml.kernel.org/r/20151221171710.GA5499@linutronix.de Signed-off-by: Ingo Molnar --- kernel/fork.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/fork.c b/kernel/fork.c index fce002e..1155eac 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -380,6 +380,7 @@ 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);