linux-kernel - Re: [PATCH RT 4/8] rtmutex: use a trylock for waiter lock in trylock

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Message-ID: <1391228495.5348.82.camel@marge.simpson.net>
Date:	Sat, 01 Feb 2014 05:21:35 +0100
From:	Mike Galbraith <bitbucket@...ine.de>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Carsten Emde <C.Emde@...dl.org>, John Kacur <jkacur@...hat.com>
Subject: Re: [PATCH RT 4/8] rtmutex: use a trylock for waiter lock in trylock

On Fri, 2014-01-31 at 23:07 +0100, Sebastian Andrzej Siewior wrote: 
> * Mike Galbraith | 2014-01-17 06:17:12 [+0100]:
> 
> >On Thu, 2014-01-16 at 23:22 -0500, Steven Rostedt wrote: 
> >> On Thu, 16 Jan 2014 04:08:57 +0100
> >> Mike Galbraith <bitbucket@...ine.de> wrote:
> >> 
> >> > On Wed, 2014-01-15 at 20:58 -0500, Steven Rostedt wrote:
> >> > 
> >> > 
> >> > > 3.2.53-rt76-rc1 stable review patch.
> >> > > If anyone has any objections, please let me know.
> >> > 
> >> > Not sure this is needed without the tglx don't unconditionally raise
> >> > timer softirq patch, and with that patch applied in the form it exists
> >> > in 3.12-rt9, as well as this one, you'll still eventually deadlock.
> >> 
> >> Hmm, I'll have to take a look. This sounds to be missing from all the
> >> stable -rt kernels. I'll be pulling in the latest updates from 3.12-rt
> >> soon.
> >
> >Below are the two deadlocks I encountered with 3.12-rt9, which has both
> >$subject and timers-do-not-raise-softirq-unconditionally.patch applied.
> 
> This patch was introduced because we had a deadlock in
> run_local_timers() which took a sleeping lock in hardirq context. This
> seem not to be the case in v3.2 therefore I would suggest not to take
> this patch here because it does not fix anything.
> 
> Mike, do you see these deadlocks with 3.12.*-rt11 as well?

No.  I beat 64 core box hard configured both nohz_idle and nohz_full,
the only thing that fell out was the nohz_full irqs enabled warning.

If Stevens patch didn't fix them, it did make them hide very well.

-Mike

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