linux-kernel - Re: [patch V4 04/10] rtmutex: No need to keep task ref for lock owner check

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Message-ID: <20140613123005.5c309e98@gandalf.local.home>
Date:	Fri, 13 Jun 2014 12:30:05 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [patch V4 04/10] rtmutex: No need to keep task ref for lock
 owner check

On Wed, 11 Jun 2014 18:44:05 -0000
Thomas Gleixner <tglx@...utronix.de> wrote:

> There is no point to keep the task ref across the check for lock
> owner. Drop the ref before that, so the protection context is clear.

You mean you deobfuscated the code ;-)

(No, patch #3 could have been called "deobfuscate the code")

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

-- Steve

> 
> Found while documenting the chain walk.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  kernel/locking/rtmutex.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> Index: tip/kernel/locking/rtmutex.c
> ===================================================================
> --- tip.orig/kernel/locking/rtmutex.c
> +++ tip/kernel/locking/rtmutex.c
> @@ -463,6 +463,8 @@ static int rt_mutex_adjust_prio_chain(st
>  
>  	/* Release the task */
>  	raw_spin_unlock_irqrestore(&task->pi_lock, flags);
> +	put_task_struct(task);
> +
>  	if (!rt_mutex_owner(lock)) {
>  		/*
>  		 * If the requeue above changed the top waiter, then we need
> @@ -472,9 +474,8 @@ static int rt_mutex_adjust_prio_chain(st
>  		if (top_waiter != rt_mutex_top_waiter(lock))
>  			wake_up_process(rt_mutex_top_waiter(lock)->task);
>  		raw_spin_unlock(&lock->wait_lock);
> -		goto out_put_task;
> +		return 0;
>  	}
> -	put_task_struct(task);
>  
>  	/* Grab the next task */
>  	task = rt_mutex_owner(lock);
> 

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