linux-kernel - Re: [RFC][PATCH 6/8] sched/rtmutex: Refactor rt_mutex

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Message-ID: <20160614140827.GB3704@worktop>
Date:	Tue, 14 Jun 2016 16:08:27 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Juri Lelli <juri.lelli@....com>
Cc:	mingo@...nel.org, tglx@...utronix.de, rostedt@...dmis.org,
	xlpang@...hat.com, linux-kernel@...r.kernel.org,
	mathieu.desnoyers@...icios.com, jdesfossez@...icios.com,
	bristot@...hat.com
Subject: Re: [RFC][PATCH 6/8] sched/rtmutex: Refactor rt_mutex_setprio()

On Tue, Jun 14, 2016 at 02:14:24PM +0100, Juri Lelli wrote:
> Hi,
> 
> still digesting this change, but I'll point out below why I think you
> are hitting a NULL ptr dereference (discussed on IRC).
> 
> On 07/06/16 21:56, Peter Zijlstra wrote:
> 
> > --- a/kernel/locking/rtmutex.c
> > +++ b/kernel/locking/rtmutex.c
> > @@ -256,61 +256,16 @@ rt_mutex_dequeue_pi(struct task_struct *
> >  	RB_CLEAR_NODE(&waiter->pi_tree_entry);
> >  }
> >  
> > +static void rt_mutex_adjust_prio(struct task_struct *p)
> >  {
> > +	struct task_struct *pi_task = NULL;
> >  
> > +	lockdep_assert_held(&p->pi_lock);
> >  
> > +	if (!task_has_pi_waiters(p))
> 
> Shouldn't this be the other way around?
> 
>  if (task_has_pi_waiters(p))
>  	pi_task = ...

Yeah, that would make more sense :-)