* Daniel Axtens <[email protected]> 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 <[email protected]>
> Cc: Ben Segall <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Signed-off-by: Daniel Axtens <[email protected]>
>
> ---
>
> 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 <[email protected]>
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 <[email protected]>
Cc: Konstantin Khlebnikov <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: [email protected]
Signed-off-by: Ingo Molnar <[email protected]>
---
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;
