linux-kernel - Re: [PATCH 2/2] sched: BUG when stack end location is over written

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Message-ID: <20140904161124.GD1436@atomlin.usersys.redhat.com>
Date:	Thu, 4 Sep 2014 17:11:24 +0100
From:	Aaron Tomlin <atomlin@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...hat.com, dzickus@...hat.com, bmr@...hat.com,
	jcastillo@...hat.com, oleg@...hat.com, pzijlstr@...hat.com,
	riel@...hat.com, linux-kernel@...r.kernel.org, tglx@...utronix.de,
	x86@...nel.org, rostedt@...dmis.org, hannes@...xchg.org,
	aneesh.kumar@...ux.vnet.ibm.com, akpm@...gle.com,
	linuxppc-dev@...ts.ozlabs.org, minchan@...nel.org
Subject: Re: [PATCH 2/2] sched: BUG when stack end location is over written

On Thu, Sep 04, 2014 at 05:32:31PM +0200, Peter Zijlstra wrote:
> On Thu, Sep 04, 2014 at 03:50:24PM +0100, Aaron Tomlin wrote:
> > Currently in the event of a stack overrun a call to schedule()
> > does not check for this type of corruption. This corruption is
> > often silent and can go unnoticed. However once the corrupted
> > region is examined at a later stage, the outcome is undefined
> > and often results in a sporadic page fault which cannot be
> > handled.
> > 
> > This patch checks for a stack overrun and takes appropriate
> > action since the damage is already done, there is no point
> > in continuing.
> > 
> > Signed-off-by: Aaron Tomlin <atomlin@...hat.com>
> > ---
> >  kernel/sched/core.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index ec1a286..d6af6a0 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -2660,6 +2660,9 @@ static noinline void __schedule_bug(struct task_struct *prev)
> >   */
> >  static inline void schedule_debug(struct task_struct *prev)
> >  {
> > +	if (unlikely(prev != &init_task &&
> > +		task_stack_end_corrupted(prev)))
> > +		BUG();
> 
> superfluous linebreak, also we appear to have BUG_ON() for situations
> just like these.
> 
> secondly, while I appreciate the 'feature' you're making schedule()
> slower for everybody, what do you propose to do about that?

Understood. I will wrap this with a suitable Kconfig option.

-- 
Aaron Tomlin
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