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

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Date:	Tue, 14 Jun 2016 12:26:38 +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.

Thanks,

	Ingo