From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757937AbcGKIWR (ORCPT ); Mon, 11 Jul 2016 04:22:17 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34826 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750760AbcGKIWP (ORCPT ); Mon, 11 Jul 2016 04:22:15 -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> To: Wanpeng Li , Konstantin Khlebnikov Cc: Peter Zijlstra , Ingo Molnar , "linux-kernel@vger.kernel.org" , stable@vger.kernel.org From: Xunlei Pang Message-ID: <57835735.6020906@redhat.com> Date: Mon, 11 Jul 2016 16:22:13 +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: 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 [10.5.110.25]); Mon, 11 Jul 2016 08:22:15 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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: pick_next_entity(): if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1) se = cfs_rq->next; Regards, Xunlei > Regards, > Wanpeng Li