Subject: Re: [PATCH 1/2] sched: Add helper for task stack page overrun checking

From: Oleg Nesterov <[email-masked]>
Date: Thu, 4 Sep 2014 17:02:34 +0200

On 09/04, Aaron Tomlin wrote:
>
> +#define task_stack_end_corrupted(task) \
> +		(*(end_of_stack(task)) != STACK_END_MAGIC)

and it is always used along with "tsk != init_task".

But why we exclude swapper/0? Can't we add

	end_of_stack(current) = STACK_END_MAGIC;

somewhere at the start of start_kernel() ?

If not, perhaps this new helper should check "task != &init_task"
itself so that we can simplify its users?

Oleg.

>  
>  static inline int object_is_on_stack(void *obj)
>  {
> diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
> index 8a4e5cb..06c7390 100644
> --- a/kernel/trace/trace_stack.c
> +++ b/kernel/trace/trace_stack.c
> @@ -13,7 +13,6 @@
>  #include <linux/sysctl.h>
>  #include <linux/init.h>
>  #include <linux/fs.h>
> -#include <linux/magic.h>
>  
>  #include <asm/setup.h>
>  
> @@ -171,8 +170,8 @@ check_stack(unsigned long ip, unsigned long *stack)
>  			i++;
>  	}
>  
> -	if ((current != &init_task &&
> -		*(end_of_stack(current)) != STACK_END_MAGIC)) {
> +	if (current != &init_task &&
> +		task_stack_end_corrupted(current)) {
>  		print_max_stack();
>  		BUG();
>  	}
> -- 
> 1.9.3
>