From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752014AbdFTK1s (ORCPT ); Tue, 20 Jun 2017 06:27:48 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:35923 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751007AbdFTK1q (ORCPT ); Tue, 20 Jun 2017 06:27:46 -0400 Date: Tue, 20 Jun 2017 12:27:42 +0200 From: Ingo Molnar To: Daniel Axtens Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, mingo@redhat.com, Konstantin Khlebnikov , Ben Segall , Thomas Gleixner Subject: [PATCH] sched/debug: Fix SCHED_WARN_ON() to return a value on !CONFIG_SCHED_DEBUG as well Message-ID: <20170620102742.p3qta5lrefhbyeen@gmail.com> References: <20170510201139.16236-1-dja@axtens.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170510201139.16236-1-dja@axtens.net> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * 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. > > 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; > + } This won't build in the !CONFIG_SCHED_DEBUG case, because of the naive definition in sched.h: #define SCHED_WARN_ON(x) ((void)(x)) That should be changed to something like: #define SCHED_WARN_ON(x) ((void)(x)) I've applied the fix below. (untested at the moment) Thanks, Ingo ========================> >>From 6d3aed3d8a0573d0a6eb1160ccd0a0713f4dbc2f Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Tue, 20 Jun 2017 12:24:42 +0200 Subject: [PATCH] sched/debug: Fix SCHED_WARN_ON() to return a value on !CONFIG_SCHED_DEBUG as well This definition of SCHED_WARN_ON(): #define SCHED_WARN_ON(x) ((void)(x)) is not fully compatible with the 'real' WARN_ON_ONCE() primitive, as it has no return value, so it cannot be used in conditionals. Fix it. Cc: Daniel Axtens Cc: Konstantin Khlebnikov Cc: Peter Zijlstra Cc: Mike Galbraith Cc: Thomas Gleixner Cc: Linus Torvalds Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar --- kernel/sched/sched.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index f2ef759a4cb6..e0329d10bdb8 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -39,9 +39,9 @@ #include "cpuacct.h" #ifdef CONFIG_SCHED_DEBUG -#define SCHED_WARN_ON(x) WARN_ONCE(x, #x) +# define SCHED_WARN_ON(x) WARN_ONCE(x, #x) #else -#define SCHED_WARN_ON(x) ((void)(x)) +# define SCHED_WARN_ON(x) ({ (void)(x), 0; }) #endif struct rq;