linux-kernel - Re: RCU lockup in the SMP idle thread, help...

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Message-ID: <alpine.LFD.2.02.1209201056531.6667@xanadu.home>
Date:	Thu, 20 Sep 2012 13:49:53 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Linus Walleij <linus.walleij@...aro.org>
cc:	paulmck@...ux.vnet.ibm.com, John Stultz <john.stultz@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	linux-kernel@...r.kernel.org
Subject: Re: RCU lockup in the SMP idle thread, help...

On Thu, 20 Sep 2012, Linus Walleij wrote:

> On Thu, Sep 20, 2012 at 2:03 AM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > Any thoughts on the feasibility of implementing NMI-based stack backtraces
> > for ARM?
> 
> Nico's department, so let's page him.

That _could_ be done, at least in theory, with some restrictions.  

However in practice ...

> In IIRC ux500 all NMIs are reserved for the secure world, so it's
> basically a no can do. :-(

That's the main issue here: not all platforms allow FIQs ( a FIQ is the 
closest to a NMI on ARM) to be available to the operating system.

However, for where this is possible, there is a patch series from Anton 
Vorontsov implementing FIQ based KGDB support which might be useful 
here.


Nicolas
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