linux-kernel - Re: [patch V3 7/7] rtmutex: Avoid pointless requeueing in the deadlock detection chain walk

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Message-ID: <20140610134745.668c8a4e@gandalf.local.home>
Date:	Tue, 10 Jun 2014 13:47:45 -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>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Jason Low <jason.low2@...com>, Brad Mouring <bmouring@...com>
Subject: Re: [patch V3 7/7] rtmutex: Avoid pointless requeueing in the
 deadlock detection chain walk

On Tue, 10 Jun 2014 19:41:39 +0200 (CEST)
Thomas Gleixner <tglx@...utronix.de> wrote:

 
> > On the loop back around, have something like:
> > 
> > 	if (top_waiter) {
> > 		if (!task_has_pi_waiters(task))
> > 			goto out_unlock_pi;
> 
> 	The task has at least one pi waiter.
>  
> > 		if (!requeue &&
> > 		    top_waiter != task_top_pi_waiter(task)) {
> > 			if (!detect_deadlock)
> > 				goto out_unlock_pi;
> > 			else
> > 				requeue = false;
> > 		}
> 
> 	Errm? if requeue is off we are in deadlock detection chainwalk
> 	mode. So all we care about is whether task is blocked on
> 	next_lock or not.

Actually that was a typo on my part. That should have been:

	if (requeue &&
		...

As we don't need to read the task_top_pi_waiter() again.

-- Steve

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