linux-kernel - Re: [PATCH -v2 2/9] sched/rtmutex/deadline: Fix a PI crash for deadline tasks

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Date:   Mon, 26 Sep 2016 11:20:58 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, tglx@...utronix.de, juri.lelli@....com,
        xlpang@...hat.com, bigeasy@...utronix.de,
        linux-kernel@...r.kernel.org, mathieu.desnoyers@...icios.com,
        jdesfossez@...icios.com, bristot@...hat.com,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH -v2 2/9] sched/rtmutex/deadline: Fix a PI crash for
 deadline tasks

> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -256,6 +256,16 @@ rt_mutex_dequeue_pi(struct task_struct *
>  	RB_CLEAR_NODE(&waiter->pi_tree_entry);
>  }
>  

Shouldn't we add a comment about what locks are expected to be held
when calling this? Especially if it can be called outside this file.

> +void rt_mutex_update_top_task(struct task_struct *p)
> +{
> +	if (!task_has_pi_waiters(p)) {
> +		p->pi_top_task = NULL;
> +		return;
> +	}
> +
> +	p->pi_top_task = task_top_pi_waiter(p)->task;
> +}
> +
>  /*
>   * Calculate task priority from the waiter tree priority
>   *
> @@ -273,10 +283,7 @@ int rt_mutex_getprio(struct task_struct
>  

Any specific locks that must be held when calling this?

>  struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
>  {
> -	if (likely(!task_has_pi_waiters(task)))
> -		return NULL;
> -
> -	return task_top_pi_waiter(task)->task;
> +	return task->pi_top_task;
>  }

-- Steve