From 58cdfe74bcde282072b3057d43264c56da748c16 Mon Sep 17 00:00:00 2001
From: Daniel Axtens <dja@axtens.net>
Date: Thu, 11 May 2017 06:11:39 +1000
Subject: [PATCH] sched/fair: WARN() and refuse to set buddy when !se->on_rq
Git-commit: c5ae366e12b2bd56fc7d7e9d484836bec9ddc110
Patch-mainline: v4.13-rc1
References: bsc#1158132
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 <dja@axtens.net>
Cc: Ben Segall <bsegall@google.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170510201139.16236-1-dja@axtens.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Matt Fleming <mfleming@suse.de>
---
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 10e60376e9c4..3651470412d8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5786,8 +5786,11 @@ 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)
@@ -5795,8 +5798,11 @@ 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)
--
2.16.4