From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754864AbcFPRGS (ORCPT ); Thu, 16 Jun 2016 13:06:18 -0400 Received: from mail-pa0-f48.google.com ([209.85.220.48]:33321 "EHLO mail-pa0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754521AbcFPRGD (ORCPT ); Thu, 16 Jun 2016 13:06:03 -0400 From: bsegall@google.com To: Konstantin Khlebnikov Cc: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] sched/fair: do not announce throttled next buddy in dequeue_task_fair References: <146608183552.21905.15924473394414832071.stgit@buzz> Date: Thu, 16 Jun 2016 10:06:00 -0700 In-Reply-To: <146608183552.21905.15924473394414832071.stgit@buzz> (Konstantin Khlebnikov's message of "Thu, 16 Jun 2016 15:57:15 +0300") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Konstantin Khlebnikov writes: > Hierarchy could be already throttled at this point. Throttled next > buddy could trigger null pointer dereference in pick_next_task_fair(). > > Signed-off-by: Konstantin Khlebnikov Reviewed-by: Ben Segall > Cc: Stable # v3.2+ > --- > kernel/sched/fair.c | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index fe809fe169d2..3c6b038cb734 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4519,15 +4519,14 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags) > > /* Don't dequeue parent if it has other entities besides us */ > if (cfs_rq->load.weight) { > + /* avoid re-evaluating load for this entity */ > + se = parent_entity(se); > /* > * Bias pick_next to pick a task from this cfs_rq, as > * p is sleeping when it is within its sched_slice. > */ > - if (task_sleep && parent_entity(se)) > - set_next_buddy(parent_entity(se)); > - > - /* avoid re-evaluating load for this entity */ > - se = parent_entity(se); > + if (task_sleep && se && !throttled_hierarchy(cfs_rq)) > + set_next_buddy(se); > break; > } > flags |= DEQUEUE_SLEEP;