From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753301AbdEIBrX (ORCPT ); Mon, 8 May 2017 21:47:23 -0400 Received: from mail-qt0-f195.google.com ([209.85.216.195]:35776 "EHLO mail-qt0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751948AbdEIBrW (ORCPT ); Mon, 8 May 2017 21:47:22 -0400 From: Daniel Axtens To: Konstantin Khlebnikov Cc: Linux Kernel Mailing List , Peter Zijlstra , Ingo Molnar , Konstantin Khlebnikov , Ben Segall , Thomas Gleixner Subject: Re: [PATCH] sched/fair: WARN and refuse to set buddy when !se->on_rq In-Reply-To: References: <20170508192250.668-1-dja@axtens.net> Date: Tue, 09 May 2017 11:47:17 +1000 Message-ID: <87k25qreca.fsf@possimpible.ozlabs.ibm.com> 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: > On Mon, May 8, 2017 at 10:22 PM, Daniel Axtens wrote: >> 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. > > Yep, this is worth debug. But I think it should be under compile-time > config option. > Something like CONFIG_DEBUG_VM which enables VM_BUG_ON and VM_WARN_ON. OK, will respin. Regards, Daniel > >> --- >> 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 >>