linux-kernel - Re: [PATCH -v5 6/5] context_tracking: fix exception_enter when already in IN

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Message-ID: <20150212170002.GH18363@lerouge>
Date:	Thu, 12 Feb 2015 18:00:03 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	paulmck@...ux.vnet.ibm.com, luto@...capital.net,
	will.deacon@....com, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, mtosatti@...hat.com, borntraeger@...ibm.com,
	lcapitulino@...hat.com, pbonzini@...hat.com
Subject: Re: [PATCH -v5 6/5] context_tracking: fix exception_enter when
 already in IN_KERNEL

On Thu, Feb 12, 2015 at 10:47:10AM -0500, Rik van Riel wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> On 02/12/2015 10:42 AM, Frederic Weisbecker wrote:
> > On Wed, Feb 11, 2015 at 02:43:19PM -0500, Rik van Riel wrote:
> >> If exception_enter happens when already in IN_KERNEL state, the 
> >> code still calls context_tracking_exit, which ends up in 
> >> rcu_eqs_exit_common, which explodes with a WARN_ON when it is 
> >> called in a situation where dynticks are not enabled.
> > 
> > Fortunately context_tracking_exit() already has a current_state ==
> > IN_KERNEL check so this shouldn't be a problem.
> 
> No, it had a hard-coded "current_state == IN_USER" check,
> which is very close, but ...
> 
> ... I replaced that with a state argument, and forgot to
> ensure that it never gets called with state == IN_KERNEL.
> This patch fixes that.

Ah that's right! Well I'm going to merge this patch to 1/5 then to
avoid breaking bisection.

Thanks.
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