From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754107AbcGKJyS (ORCPT ); Mon, 11 Jul 2016 05:54:18 -0400 Received: from mail-oi0-f52.google.com ([209.85.218.52]:33264 "EHLO mail-oi0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751182AbcGKJyR (ORCPT ); Mon, 11 Jul 2016 05:54:17 -0400 MIME-Version: 1.0 In-Reply-To: <57835BFD.90201@redhat.com> References: <146608183552.21905.15924473394414832071.stgit@buzz> <57835735.6020906@redhat.com> <57835BFD.90201@redhat.com> From: Wanpeng Li Date: Mon, 11 Jul 2016 17:54:16 +0800 Message-ID: Subject: Re: [PATCH] sched/fair: do not announce throttled next buddy in dequeue_task_fair To: xlpang@redhat.com Cc: Konstantin Khlebnikov , Peter Zijlstra , Ingo Molnar , "linux-kernel@vger.kernel.org" , stable@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Konstantin, Xunlei, 2016-07-11 16:42 GMT+08:00 Xunlei Pang : > On 2016/07/11 at 16:22, Xunlei Pang wrote: >> On 2016/07/11 at 15:25, Wanpeng Li wrote: >>> 2016-06-16 20:57 GMT+08:00 Konstantin Khlebnikov : >>>> Hierarchy could be already throttled at this point. Throttled next >>>> buddy could trigger null pointer dereference in pick_next_task_fair(). >>> There is cfs_rq->next check in pick_next_entity(), so how can null >>> pointer dereference happen? >> I guess it's the following code leading to a NULL se returned: > > s/NULL/empty-entity cfs_rq se/ > >> pick_next_entity(): >> if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1) ^^^^^^^^^^^^^ I think this will return false. Regards, Wanpeng Li