From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([198.137.202.9]:36429 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756380AbcJGI36 (ORCPT ); Fri, 7 Oct 2016 04:29:58 -0400 Date: Fri, 7 Oct 2016 10:29:50 +0200 From: Peter Zijlstra To: Mike Galbraith Cc: stable , Ingo Molnar , Oleg Nesterov , linux-tip-commits Subject: Re: [tip:locking/core] sched/core: Fix an SMP ordering race in try_to_wake_up() vs. schedule() Message-ID: <20161007082950.GS3142@twins.programming.kicks-ass.net> References: <1475804215.4075.13.camel@gmx.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1475804215.4075.13.camel@gmx.de> Sender: stable-owner@vger.kernel.org List-ID: On Fri, Oct 07, 2016 at 03:36:55AM +0200, Mike Galbraith wrote: > Seems this may be one of those not so theoretical races. A humongous > ppc64 box actually managed to run a task on two cores.. briefly. Cute :-) Why was you running a year old kernel on that box anyway? ;-) > Stable material methinks. Yep.. > On Fri, 2015-12-04 at 03:53 -0800, tip-bot for Peter Zijlstra wrote: > > Commit-ID: ecf7d01c229d11a44609c0067889372c91fb4f36 > > Gitweb: http://git.kernel.org/tip/ecf7d01c229d11a44609c0067889372c91fb4f36 > > Author: Peter Zijlstra > > AuthorDate: Wed, 7 Oct 2015 14:14:13 +0200 > > Committer: Ingo Molnar > > CommitDate: Fri, 4 Dec 2015 10:26:43 +0100 > > > > sched/core: Fix an SMP ordering race in try_to_wake_up() vs. schedule() > > > > Oleg noticed that its possible to falsely observe p->on_cpu == 0 such > > that we'll prematurely continue with the wakeup and effectively run p on > > two CPUs at the same time.