linux-kernel - Re: [PATCH] PM / devfreq: missing rcu_read_lock() added for find_device

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Date:	Thu, 22 Nov 2012 14:09:28 +0000
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	MyungJoo Ham <myungjoo.ham@...sung.com>
Cc:	serge@...lyn.com, myungjoo.ham@...il.com, linux-pm@...r.kernel.org,
	rjw@...k.pl, keescook@...omium.org, serge.hallyn@...onical.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PM / devfreq: missing rcu_read_lock() added for
 find_device_opp()

Quoting MyungJoo Ham (myungjoo.ham@...sung.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@...onical.com>

> Reported-by: Kees Cook <keescook@...omium.org>
> Signed-off-by: MyungJoo Ham <myungjoo.ham@...sung.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@...sung.com>");
> -- 
> 1.7.5.4
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