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From: WANG Chao <wcwxyz@gmail.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] sched: unlikely corrupted stack end
Date: Wed, 15 Jun 2016 00:55:02 +0800	[thread overview]
Message-ID: <71E4B9CB-BF33-4319-941B-85EC6640E339@gmail.com> (raw)
In-Reply-To: <20160614102638.GB13439@gmail.com>


> 在 2016年6月14日,下午6:26,Ingo Molnar <mingo@kernel.org> 写道:
> 
> 
> * WANG Chao <wcwxyz@gmail.com> wrote:
> 
>> 
>>> 在 2016年6月14日,下午4:56,Ingo Molnar <mingo@kernel.org> 写道:
>>> 
>>> 
>>> * WANG Chao <wcwxyz@gmail.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@gmail.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

  reply	other threads:[~2016-06-14 16:55 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-14  6:43 [PATCH] " WANG Chao
2016-06-14  7:43 ` Ingo Molnar
2016-06-14  8:17 ` Peter Zijlstra
2016-06-14  8:24 ` [PATCH v2] " WANG Chao
2016-06-14  8:56   ` Ingo Molnar
2016-06-14 10:17     ` WANG Chao
2016-06-14 10:26       ` Ingo Molnar
2016-06-14 16:55         ` WANG Chao [this message]
2016-06-15  8:25           ` Ingo Molnar
2016-06-15  8:53             ` [PATCH v3] " WANG Chao
2016-06-14  9:08   ` [PATCH v2] " kbuild test robot

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