linux-kernel - Re: [PATCH v2] sched: unlikely corrupted stack end

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Date:	Tue, 14 Jun 2016 10:56:13 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	WANG Chao <wcwxyz@...il.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched: unlikely corrupted stack end


* WANG Chao <wcwxyz@...il.com> wrote:

> unlikely() was dropped in commit ce03e4137bb2 ("sched/core: Drop
> unlikely behind BUG_ON()"), but commit 29d6455178a0 ("sched: panic on
> corrupted stack end") dropped BUG_ON() and called panic directly.
> 
> Now we should bring unlikely() back for branch prediction. While we're
> at it, it's better and cleaner to turn task_stack_end_corrupted() into
> inline function.
> 
> Signed-off-by: WANG Chao <wcwxyz@...il.com>
> ---
>  include/linux/sched.h | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 6e42ada26345..797ca1975431 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2997,8 +2997,11 @@ static inline unsigned long *end_of_stack(struct task_struct *p)
>  }
>  
>  #endif
> -#define task_stack_end_corrupted(task) \
> -		(*(end_of_stack(task)) != STACK_END_MAGIC)
> +
> +static inline int task_stack_end_corrupted(struct task_struct *p)
> +{
> +	return unlikely(*(end_of_stack(p)) != STACK_END_MAGIC);
> +}

The passed in pointer should be const, and the extra parentheses around the 
end_of_stack() call are not needed anymore (since it's now proper C code now).

Thanks,

	Ingo