From c5ae366e12b2bd56fc7d7e9d484836bec9ddc110 Mon Sep 17 00:00:00 2001 From: Daniel Axtens Date: Thu, 11 May 2017 06:11:39 +1000 Subject: [PATCH] sched/fair: WARN() and refuse to set buddy when !se->on_rq 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: https://marc.info/?l=linux-kernel&m=146651668921468&w=2 https://lkml.org/lkml/2016/6/16/663 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. Just do it. Signed-off-by: Daniel Axtens Cc: Ben Segall Cc: Konstantin Khlebnikov Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20170510201139.16236-1-dja@axtens.net Signed-off-by: Ingo Molnar --- 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 396bca9c7996..cb3a3da7089f 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6164,8 +6164,11 @@ 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) @@ -6173,8 +6176,11 @@ 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)