linux-kernel - Re: rcu warnings cause stack overflow

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Date:	Thu, 2 Feb 2012 15:52:20 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: rcu warnings cause stack overflow

On Thu, Feb 02, 2012 at 01:27:42PM +0100, Heiko Carstens wrote:
> On Wed, Feb 01, 2012 at 04:14:48PM +0100, Frederic Weisbecker wrote:
> > > Removing the WARN_ON_ONCE will fix this and, if lockdep is turned on, still
> > > will find illegal uses. But it won't work for lockdep off configs...
> > > So we probably want something better than the patch below.
> > 
> > Ah ok. Hmm, but why are you using an exception to implement WARN_ON()
> > in s390? Is it to have a whole new stack for the warning path in order
> > to avoid stack overflow from the place that called the WARN_ON() ?
> 
> The reason was to reduce the code footprint of the WARN_ON() and also
> be able to print the register contents at the time the warning happened.

Ah ok, makes sense.

> 
> All architectures which define __WARN_TAINT implement warnings with
> exceptions. Currently that are parisc, powerpc, s390 and sh.
> 
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