Subject: Re: [PATCH 2/2] sched: BUG when stack end location is over written

From: Peter Zijlstra <[email-masked]>
Date: Thu, 4 Sep 2014 17:32:31 +0200

On Thu, Sep 04, 2014 at 03:50:24PM +0100, Aaron Tomlin wrote:
> Currently in the event of a stack overrun a call to schedule()
> does not check for this type of corruption. This corruption is
> often silent and can go unnoticed. However once the corrupted
> region is examined at a later stage, the outcome is undefined
> and often results in a sporadic page fault which cannot be
> handled.
> 
> This patch checks for a stack overrun and takes appropriate
> action since the damage is already done, there is no point
> in continuing.
> 
> Signed-off-by: Aaron Tomlin <[email-masked]>
> ---
>  kernel/sched/core.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index ec1a286..d6af6a0 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2660,6 +2660,9 @@ static noinline void __schedule_bug(struct task_struct *prev)
>   */
>  static inline void schedule_debug(struct task_struct *prev)
>  {
> +	if (unlikely(prev != &init_task &&
> +		task_stack_end_corrupted(prev)))
> +		BUG();

superfluous linebreak, also we appear to have BUG_ON() for situations
just like these.

secondly, while I appreciate the 'feature' you're making schedule()
slower for everybody, what do you propose to do about that?