Quoting MyungJoo Ham (myungjoo....@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.hal...@canonical.com>
> Reported-by: Kees Cook <keesc...@chromium.org>
> Signed-off-by: MyungJoo Ham <myungjoo....@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....@samsung.com>");
> --
> 1.7.5.4
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