From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Serge E. Hallyn" <serge@hallyn.com>
Subject: Re: [PATCH] PM / devfreq: missing rcu_read_lock() added for
 find_device_opp()
Date: Thu, 22 Nov 2012 14:09:28 +0000
Message-ID: <20121122140928.GA14567@mail.hallyn.com>
References: <20121121134621.GA30575@mail.hallyn.com>
 <1353566192-7079-1-git-send-email-myungjoo.ham@samsung.com>
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To: MyungJoo Ham <myungjoo.ham@samsung.com>
Cc: serge@hallyn.com, myungjoo.ham@gmail.com, linux-pm@vger.kernel.org, rjw@sisk.pl, keescook@chromium.org, serge.hallyn@canonical.com, linux-kernel@vger.kernel.org
List-Id: linux-pm@vger.kernel.org

Quoting MyungJoo Ham (myungjoo.ham@samsung.com):
> opp_get_notifier() uses find_device_opp(), which requires to
> held rcu_read_lock. In order to keep the notifier-header
> valid, we have added rcu_read_lock().
> 

Reviewed-by: Serge Hallyn <serge.hallyn@canonical.com>

> Reported-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
> ---
>  drivers/devfreq/devfreq.c |   26 ++++++++++++++++++++------
>  1 files changed, 20 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 1388d46..5275883 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -1023,11 +1023,18 @@ struct opp *devfreq_recommended_opp(struct device *dev, unsigned long *freq,
>   */
>  int devfreq_register_opp_notifier(struct device *dev, struct devfreq *devfreq)
>  {
> -	struct srcu_notifier_head *nh = opp_get_notifier(dev);
> +	struct srcu_notifier_head *nh;
> +	int ret = 0;
>  
> +	rcu_read_lock();
> +	nh = opp_get_notifier(dev);
>  	if (IS_ERR(nh))
> -		return PTR_ERR(nh);
> -	return srcu_notifier_chain_register(nh, &devfreq->nb);
> +		ret = PTR_ERR(nh);
> +	rcu_read_unlock();
> +	if (!ret)
> +		ret = srcu_notifier_chain_register(nh, &devfreq->nb);
> +
> +	return ret;
>  }
>  
>  /**
> @@ -1042,11 +1049,18 @@ int devfreq_register_opp_notifier(struct device *dev, struct devfreq *devfreq)
>   */
>  int devfreq_unregister_opp_notifier(struct device *dev, struct devfreq *devfreq)
>  {
> -	struct srcu_notifier_head *nh = opp_get_notifier(dev);
> +	struct srcu_notifier_head *nh;
> +	int ret = 0;
>  
> +	rcu_read_lock();
> +	nh = opp_get_notifier(dev);
>  	if (IS_ERR(nh))
> -		return PTR_ERR(nh);
> -	return srcu_notifier_chain_unregister(nh, &devfreq->nb);
> +		ret = PTR_ERR(nh);
> +	rcu_read_unlock();
> +	if (!ret)
> +		ret = srcu_notifier_chain_unregister(nh, &devfreq->nb);
> +
> +	return ret;
>  }
>  
>  MODULE_AUTHOR("MyungJoo Ham <myungjoo.ham@samsung.com>");
> -- 
> 1.7.5.4