From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from forward-corp1m.cmail.yandex.net ([5.255.216.100]:50890 "EHLO forward-corp1m.cmail.yandex.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030341AbcGKIQP (ORCPT ); Mon, 11 Jul 2016 04:16:15 -0400 Subject: Re: [PATCH] sched/fair: do not announce throttled next buddy in dequeue_task_fair To: Wanpeng Li References: <146608183552.21905.15924473394414832071.stgit@buzz> Cc: Peter Zijlstra , Ingo Molnar , "linux-kernel@vger.kernel.org" , stable@vger.kernel.org From: Konstantin Khlebnikov Message-ID: <578355AC.2090507@yandex-team.ru> Date: Mon, 11 Jul 2016 11:15:40 +0300 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org List-ID: On 11.07.2016 10:25, 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? > If we nominate task from throttled hiearchy as a next buddy then at some level in pick_next_task_fair we could pick cfs_rq which has no runnable entities - in pick_next_entiry both "curr" and "left" are NULL. -- Konstantin