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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 10 Jun 2014 22:45:11 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Steven Rostedt <rostedt@...dmis.org>
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, Steven Rostedt wrote:

> 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.

     if (requeue ...

is completely pointless as the code you were talking about is in the

   if (!requeue) {

branch. So what?

Thanks,

	tglx
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/