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

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Date:	Wed, 15 Jun 2016 10:25:54 +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:

> 
> > 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?

Oh well ...

I guess we'll have to add the unlikely() to the macro itself.

Thanks,

	Ingo