linux-kernel - Re: [patch 2/2] rtmutex: Detect changes in the pi lock chain

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Date:	Fri, 6 Jun 2014 05:58:29 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, Brad Mouring <bmouring@...com>
Subject: Re: [patch 2/2] rtmutex: Detect changes in the pi lock chain

On Fri, 6 Jun 2014 11:48:59 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> 
> 
> hehe, I can almost follow this code :-)
> 
> How about something like this on top?

Acked-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve

> 
> ---
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -260,6 +260,11 @@ static void rt_mutex_adjust_prio(struct
>   */
>  int max_lock_depth = 1024;
>  
> +static inline struct rt_mutex *task_blocked_on(struct task_struct *p)
> +{
> +	return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
> +}
> +
>  /*
>   * Adjust the priority chain. Also used for deadlock detection.
>   * Decreases task's usage by one - may thus free the task.
> @@ -443,10 +448,7 @@ static int rt_mutex_adjust_prio_chain(st
>  	 * blocked itself. If yes we store a pointer to the lock for
>  	 * the lock chain change detection above.
>  	 */
> -	if (task->pi_blocked_on)
> -		next_lock = task->pi_blocked_on->lock;
> -	else
> -		next_lock = NULL;
> +	next_lock = task_blocked_on(task);
>  
>  	raw_spin_unlock_irqrestore(&task->pi_lock, flags);
>  
> @@ -569,7 +571,7 @@ static int task_blocks_on_rt_mutex(struc
>  {
>  	struct task_struct *owner = rt_mutex_owner(lock);
>  	struct rt_mutex_waiter *top_waiter = waiter;
> -	struct rt_mutex *next_lock = NULL;
> +	struct rt_mutex *next_lock;
>  	unsigned long flags;
>  	int chain_walk, res;
>  
> @@ -614,8 +616,8 @@ static int task_blocks_on_rt_mutex(struc
>  	} else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock)) {
>  		chain_walk = 1;
>  	}
> -	if (owner->pi_blocked_on)
> -		next_lock = owner->pi_blocked_on->lock;
> +
> +	next_lock = task_blocked_on(owner);
>  
>  	raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
>  	if (!chain_walk)
> @@ -705,8 +707,7 @@ static void remove_waiter(struct rt_mute
>  		}
>  		__rt_mutex_adjust_prio(owner);
>  
> -		if (owner->pi_blocked_on)
> -			next_lock = owner->pi_blocked_on->lock;
> +		next_lock = task_blocked_on(owner);
>  
>  		raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
>  	}

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