Date: Wed, 11 Feb 2015 13:27:23 -0800
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Rik van Riel <riel@redhat.com>
Cc: fweisbec@gmail.com, luto@amacapital.net, will.deacon@arm.com,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org, mtosatti@redhat.com,
        borntraeger@de.ibm.com, lcapitulino@redhat.com, pbonzini@redhat.com
Subject: Re: [PATCH -v5 6/5] context_tracking: fix exception_enter when
 already in IN_KERNEL
Message-ID: <20150211212723.GN4166@linux.vnet.ibm.com>
Reply-To: paulmck@linux.vnet.ibm.com
References: <1423600074-2907-1-git-send-email-riel@redhat.com>
 <20150211144319.2a0c29d6@cuia.bos.redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20150211144319.2a0c29d6@cuia.bos.redhat.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1602
Lines: 45

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.
> 
> This can be avoided by having exception_enter only switch to
> IN_KERNEL state if the current state is not already IN_KERNEL.

Ugh...  Time to formally verify, sounds like...

							Thanx, Paul

> Signed-off-by: Rik van Riel <riel@redhat.com>
> Reported-by: Luiz Capitulino <lcapitulino@redhat.com>
> ---
> Frederic, you will want this "bonus" patch, too :)
> 
> Thanks to Luiz for finding this one. Whatever I was running did not
> trigger this issue...
> 
>  include/linux/context_tracking.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
> index b65fd1420e53..9da230406e8c 100644
> --- a/include/linux/context_tracking.h
> +++ b/include/linux/context_tracking.h
> @@ -37,7 +37,8 @@ static inline enum ctx_state exception_enter(void)
>  		return 0;
> 
>  	prev_ctx = this_cpu_read(context_tracking.state);
> -	context_tracking_exit(prev_ctx);
> +	if (prev_ctx != IN_KERNEL)
> +		context_tracking_exit(prev_ctx);
> 
>  	return prev_ctx;
>  }
> 

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/