linux-kernel - Re: kernel deadlock

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Message-ID: <20130910072908.GA32257@gmail.com>
Date:	Tue, 10 Sep 2013 09:29:09 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Gerlando Falauto <gerlando.falauto@...mile.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Richard Cochran <richardcochran@...il.com>,
	Prarit Bhargava <prarit@...hat.com>,
	"Brunck, Holger" <Holger.Brunck@...mile.com>,
	"Longchamp, Valentin" <Valentin.Longchamp@...mile.com>,
	"Bigler, Stefan" <Stefan.Bigler@...mile.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: kernel deadlock


* John Stultz <john.stultz@...aro.org> wrote:

> Now, I'm still in the dark as to why HRTICK exposes this, but seems like 
> the following patch should resolve the issue (and quiets the lockdep 
> warnings in my testing). Let me know how it works for you!
> 
> Ingo: This makes me think we really should have some lockdep smarts 
> added to seqlock/seqcount structures. Is there something already 
> discovered thats preventing this, or has this just not yet been tried?

There's no fundamental reason to not do it, it's a very good idea!

> From 09885df9734aa678ccb61dbef356fea4faeff16c Mon Sep 17 00:00:00 2001
> From: John Stultz <john.stultz@...aro.org>
> Date: Mon, 9 Sep 2013 13:07:18 -0700
> Subject: [PATCH] timekeepeing: Fix HRTICK related deadlock from ntp lock changes

Cool fix! I think I've seen this deadlock in various incarnations but was 
never able to track it down. Do you have a guesstimate about roughly when 
it was introduced? Is it an ancient bug?

Thanks,

	Ingo
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