linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <20141120143626.GA2542@lerouge>
Date:	Thu, 20 Nov 2014 15:36:32 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Dave Jones <davej@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Don Zickus <dzickus@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: frequent lockups in 3.18rc4

On Wed, Nov 19, 2014 at 12:15:24AM -0500, Dave Jones wrote:
> On Tue, Nov 18, 2014 at 08:40:55PM -0800, Linus Torvalds wrote:
> 
>  > Hmm, if we are getting soft-lockups here, maybe it suggest too much exit-work.
>  > 
>  > Some TIF_NOHZ loop, perhaps? You have nohz on, don't you?
>  > 
>  > That makes me wonder: does the problem go away if you disable NOHZ?
> 
> Does nohz=off do enough ? I couldn't convince myself after looking at
> dmesg, and still seeing dynticks stuff in there.
> 
> I'll do a rebuild with all the CONFIG_NO_HZ stuff off, though it also changes
> some other config stuff wrt timers.

You also need to disable context tracking. So you need to deactive also
CONFIG_RCU_USER_QS and CONFIG_CONTEXT_TRACKING_FORCE and eventually make sure
nothing else is turning on CONFIG_CONTEXT_TRACKING.

You can keep CONFIG_NO_HZ_IDLE though, just not CONFIG_NO_HZ_FULL.
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