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

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Message-Id: <71E4B9CB-BF33-4319-941B-85EC6640E339@gmail.com>
Date:	Wed, 15 Jun 2016 00:55:02 +0800
From:	WANG Chao <wcwxyz@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
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


> 在 2016年6月14日，下午6:26，Ingo Molnar <mingo@...nel.org> 写道：
> 
> 
> * WANG Chao <wcwxyz@...il.com> wrote:
> 
>> 
>>> 在 2016年6月14日，下午4:56，Ingo Molnar <mingo@...nel.org> 写道：
>>> 
>>> 
>>> * 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).
>> 
>> end_of_stack() will discard const and cause an compiler warning.
>> Should I add const to end_of_stack()?
> 
> Yes. Also make sure ia64 still builds and such.

It seems convert task_stack_end_corrupted() into inline isn’t trivial.

In ia64, end_of_stack() is expanded to:

(unsigned long *)((void *)(p) + ((IA64_TASK_SIZE + IA64_THREAD_INFO_SIZE + 31) & ~31))

IA64_TASK_SIZE and IA64_THREAD_INFO_SIZE is defined in arch/ia64/kernel/asm-offsets.c,
which needs to include linux/sched.h.

So the problem is task_stack_end_corrupted() doesn’t compile before asm-offsets.c is compiled.
asm-offsets.c also needs to include linux/sched.h to compile. I think maybe that’s why
task_stack_end_corrupted() is introduced as marco, not inline.

Any idea?

Thanks
WANG Chao