From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755695AbdEHTX2 (ORCPT ); Mon, 8 May 2017 15:23:28 -0400 Received: from mail-qt0-f196.google.com ([209.85.216.196]:36483 "EHLO mail-qt0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752364AbdEHTX0 (ORCPT ); Mon, 8 May 2017 15:23:26 -0400 From: Daniel Axtens To: linux-kernel@vger.kernel.org, peterz@infradead.org, mingo@redhat.com, Konstantin Khlebnikov Cc: Daniel Axtens , Ben Segall , Thomas Gleixner Subject: [PATCH] sched/fair: WARN and refuse to set buddy when !se->on_rq Date: Tue, 9 May 2017 05:22:50 +1000 Message-Id: <20170508192250.668-1-dja@axtens.net> X-Mailer: git-send-email 2.11.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If we set a next or last buddy for a se that is not on_rq, we will end up taking a NULL pointer dereference in wakeup_preempt_entity via pick_next_task_fair. Detect when we would be about to do that, throw a warning and then refuse to actually set it. This has been suggested at least twice[0][1]: just do it. [0] https://marc.info/?l=linux-kernel&m=146651668921468&w=2 [1] https://lkml.org/lkml/2016/6/16/663 Cc: Konstantin Khlebnikov Cc: Ben Segall Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Daniel Axtens --- I recently had to debug a problem with these (we hadn't backported Konstantin's patches in this area) and this would have saved a lot of time/pain. --- kernel/sched/fair.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index d71109321841..9b988815b4ad 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6168,8 +6168,11 @@ static void set_last_buddy(struct sched_entity *se) if (entity_is_task(se) && unlikely(task_of(se)->policy == SCHED_IDLE)) return; - for_each_sched_entity(se) + for_each_sched_entity(se) { + if (WARN_ON_ONCE(!se->on_rq)) + return; cfs_rq_of(se)->last = se; + } } static void set_next_buddy(struct sched_entity *se) @@ -6177,8 +6180,11 @@ static void set_next_buddy(struct sched_entity *se) if (entity_is_task(se) && unlikely(task_of(se)->policy == SCHED_IDLE)) return; - for_each_sched_entity(se) + for_each_sched_entity(se) { + if (WARN_ON_ONCE(!se->on_rq)) + return; cfs_rq_of(se)->next = se; + } } static void set_skip_buddy(struct sched_entity *se) -- 2.11.0