linux-kernel - Re: [PATCH RT 00/39] Linux 3.14.34-rt32-rc1

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Date:	Mon, 16 Mar 2015 10:02:05 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	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>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: Re: [PATCH RT 00/39] Linux 3.14.34-rt32-rc1

On Mon, 16 Mar 2015 14:59:10 +0100
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> * Steven Rostedt | 2015-03-12 15:13:07 [-0400]:
> 
> >Please scream at me if I messed something up. Please test the patches too.
> 
> So Paul remided us about the dead lock thingy that has been reported.
> Users reported that it does not occur with v3.18-RT and they think it is
> due to 'Revert "timers: do not raise softirq unconditionally"' in 
> Revert-timers-do-not-raise-softirq-unconditionally.patch.
> 
> I reverted it because I couldn't get highres to get to work at all on
> v3.18 due to different synchronisation / expectaion of the timer
> framework. Since the trylock might record a different lock owner it is
> possible that this causes the deadlock (it thinks). Therefore it has no
> stable tag nor any reference to the deadlock problem.

I guess the question is, is there any other place that does a trylock
in hard irq context? If so, the revert isn't going to fix it.

-- Steve

> 
> With this patch applied FULL_NOHZ should not properly work (again) due
> to timer softirq wake ups (but this is a different problem).
> 
> Sebastian

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