linux-kernel - Re: [PATCH v3 2/6] sched/rtmutex/deadline: Fix a PI crash for deadline tasks

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Message-ID: <20160420131932.GC3430@twins.programming.kicks-ass.net>
Date:	Wed, 20 Apr 2016 15:19:32 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Xunlei Pang <xlpang@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Juri Lelli <juri.lelli@....com>,
	Ingo Molnar <mingo@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v3 2/6] sched/rtmutex/deadline: Fix a PI crash for
 deadline tasks

On Thu, Apr 14, 2016 at 07:37:03PM +0800, Xunlei Pang wrote:
> +	/* Updated under pi_lock and rtmutex lock */
>  	struct rb_node *pi_waiters_leftmost;
> +	struct rb_node *pi_waiters_leftmost_copy;

>  struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
>  {
> +	if (!task->pi_waiters_leftmost_copy)
>  		return NULL;
>  
> +	return rb_entry(task->pi_waiters_leftmost_copy,
> +				struct rt_mutex_waiter, pi_tree_entry)->task;
>  }

why ?! Why not keep a regular task_struct pointer and avoid this stuff?