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Date:	Wed, 24 Dec 2014 10:28:42 -0600
From:	Nishanth Menon <nm@...com>
To:	Dmitry Torokhov <dtor@...omium.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Viresh Kumar <viresh.kumar@...aro.org>
CC:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Stefan Wahren <stefan.wahren@...e.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	<linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] PM / OPP: add some lockdep annotations

On 12/16/2014 05:09 PM, Dmitry Torokhov wrote:
> Certain OPP APIs need to be called under RCU lock; let's add a few
> rcu_lockdep_assert() calls to warn about potential misuse.
> 
> Signed-off-by: Dmitry Torokhov <dtor@...omium.org>
> ---
>  drivers/base/power/opp.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
> index d24dd614a..b78c14d 100644
> --- a/drivers/base/power/opp.c
> +++ b/drivers/base/power/opp.c
> @@ -108,6 +108,14 @@ static LIST_HEAD(dev_opp_list);
>  /* Lock to allow exclusive modification to the device and opp lists */
>  static DEFINE_MUTEX(dev_opp_list_lock);
>  
> +#define opp_rcu_lockdep_assert()					\
> +do {									\
> +	rcu_lockdep_assert(rcu_read_lock_held() ||			\
> +				lockdep_is_held(&dev_opp_list_lock),	\
> +			   "Missing rcu_read_lock() or "		\
> +			   "dev_opp_list_lock protection");		\
> +} while (0)
> +
>  /**
>   * find_device_opp() - find device_opp struct using device pointer
>   * @dev:	device pointer used to lookup device OPPs
> @@ -218,6 +226,8 @@ int dev_pm_opp_get_opp_count(struct device *dev)
>  	struct dev_pm_opp *temp_opp;
>  	int count = 0;
>  
> +	opp_rcu_lockdep_assert();
> +
>  	dev_opp = find_device_opp(dev);
>  	if (IS_ERR(dev_opp)) {
>  		int r = PTR_ERR(dev_opp);
> @@ -267,6 +277,8 @@ struct dev_pm_opp *dev_pm_opp_find_freq_exact(struct device *dev,
>  	struct device_opp *dev_opp;
>  	struct dev_pm_opp *temp_opp, *opp = ERR_PTR(-ERANGE);
>  
> +	opp_rcu_lockdep_assert();
> +
>  	dev_opp = find_device_opp(dev);
>  	if (IS_ERR(dev_opp)) {
>  		int r = PTR_ERR(dev_opp);
> @@ -313,6 +325,8 @@ struct dev_pm_opp *dev_pm_opp_find_freq_ceil(struct device *dev,
>  	struct device_opp *dev_opp;
>  	struct dev_pm_opp *temp_opp, *opp = ERR_PTR(-ERANGE);
>  
> +	opp_rcu_lockdep_assert();
> +
>  	if (!dev || !freq) {
>  		dev_err(dev, "%s: Invalid argument freq=%p\n", __func__, freq);
>  		return ERR_PTR(-EINVAL);
> @@ -361,6 +375,8 @@ struct dev_pm_opp *dev_pm_opp_find_freq_floor(struct device *dev,
>  	struct device_opp *dev_opp;
>  	struct dev_pm_opp *temp_opp, *opp = ERR_PTR(-ERANGE);
>  
> +	opp_rcu_lockdep_assert();
> +
>  	if (!dev || !freq) {
>  		dev_err(dev, "%s: Invalid argument freq=%p\n", __func__, freq);
>  		return ERR_PTR(-EINVAL);
> 

You should also add opp_rcu_lockdep_assert to the following functions:
dev_pm_opp_get_voltage and dev_pm_opp_get_freq - both of which must be
used under rcu read lock.

dev_pm_opp_get_notifier references the RCU protected dev_opp list ->
so that must also be under rcu read lock.


love the concept, and I suggest splitting this into the following:

RCU readers: trivial as rcu_read_lock_help dumps
RCU updates: (adding, updating, removing): for the helper functions
ensure mutex_lock held assertion.



-- 
Regards,
Nishanth Menon
--
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