From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030281AbcGKImm (ORCPT ); Mon, 11 Jul 2016 04:42:42 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37567 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751743AbcGKIml (ORCPT ); Mon, 11 Jul 2016 04:42:41 -0400 Reply-To: xlpang@redhat.com Subject: Re: [PATCH] sched/fair: do not announce throttled next buddy in dequeue_task_fair References: <146608183552.21905.15924473394414832071.stgit@buzz> <57835735.6020906@redhat.com> To: Wanpeng Li , Konstantin Khlebnikov Cc: Peter Zijlstra , Ingo Molnar , "linux-kernel@vger.kernel.org" , stable@vger.kernel.org From: Xunlei Pang Message-ID: <57835BFD.90201@redhat.com> Date: Mon, 11 Jul 2016 16:42:37 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <57835735.6020906@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Mon, 11 Jul 2016 08:42:40 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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) > se = cfs_rq->next; > > Regards, > Xunlei > >> Regards, >> Wanpeng Li