Re: [RFC][PATCH 6/8] sched/rtmutex: Refactor rt_mutex_setprio()

From: Peter Zijlstra <peterz@infradead.org>
To: Juri Lelli <juri.lelli@arm.com>
Cc: mingo@kernel.org, tglx@linutronix.de, rostedt@goodmis.org,
	xlpang@redhat.com, linux-kernel@vger.kernel.org,
	mathieu.desnoyers@efficios.com, jdesfossez@efficios.com,
	bristot@redhat.com
Subject: Re: [RFC][PATCH 6/8] sched/rtmutex: Refactor rt_mutex_setprio()
Date: Tue, 14 Jun 2016 16:08:27 +0200	[thread overview]
Message-ID: <20160614140827.GB3704@worktop> (raw)
In-Reply-To: <20160614131424.GK5981@e106622-lin>

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 :-)