From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750927AbdFSOGC (ORCPT ); Mon, 19 Jun 2017 10:06:02 -0400 Received: from mail-pf0-f194.google.com ([209.85.192.194]:36454 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750782AbdFSOGB (ORCPT ); Mon, 19 Jun 2017 10:06:01 -0400 From: Daniel Axtens To: linux-kernel@vger.kernel.org, peterz@infradead.org, mingo@redhat.com, Konstantin Khlebnikov Cc: Ben Segall , Thomas Gleixner Subject: Re: [PATCH v2] sched/fair: WARN and refuse to set buddy when !se->on_rq In-Reply-To: <20170510201139.16236-1-dja@axtens.net> References: <20170510201139.16236-1-dja@axtens.net> Date: Tue, 20 Jun 2017 00:05:52 +1000 Message-ID: <8760fskr7j.fsf@linkitivity.dja.id.au> 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 Hi Konstantin and Peter, Just checking if this version was OK with you - I hadn't heard anything and I noticed it's not in -next so I just wanted to check to see if there were any other changes you wanted. Regards, Daniel Daniel Axtens writes: > 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. > > v2: use SCHED_WARN_ON to restrict when the test is run. This is a > macro for WARN_ON_ONCE, which is convenient. > --- > 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..44b94cfe02cb 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 (SCHED_WARN_ON(!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 (SCHED_WARN_ON(!se->on_rq)) > + return; > cfs_rq_of(se)->next = se; > + } > } > > static void set_skip_buddy(struct sched_entity *se) > -- > 2.11.0