Re: [PATCH v2 3/5] OPP: Allow notifiers to call dev_pm_opp_get_{voltage,freq} RCU-free

Viresh Kumar
2015-09-22T17:10:38Z

On 18-09-15, 17:52, Stephen Boyd wrote:
> We pass the dev_pm_opp structure to OPP notifiers but the users
> of the notifier need to surround calls to dev_pm_opp_get_*() with
> RCU read locks to avoid lockdep warnings. The notifier is already
> called with the dev_opp's srcu lock held, so it should be safe to
> assume the devm_pm_opp structure is already protected inside the
> notifier. Update the lockdep check for this.
>
> Cc: Krzysztof Kozlowski <k.kozlowski@samsung.com>
> Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
> ---
> drivers/base/power/opp.c | 19 +++++++++++--------
> 1 file changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
> index 35b66c46dcb7..1d8c45e53245 100644
> --- a/drivers/base/power/opp.c
> +++ b/drivers/base/power/opp.c
> @@ -146,9 +146,10 @@ 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() \
> +#define opp_rcu_lockdep_assert(s) \
> do { \
> RCU_LOCKDEP_WARN(!rcu_read_lock_held() && \
> + !(s && srcu_read_lock_held(s)) && \
> !lockdep_is_held(&dev_opp_list_lock), \
> "Missing rcu_read_lock() or " \
> "dev_opp_list_lock protection"); \
> @@ -236,9 +237,10 @@ unsigned long dev_pm_opp_get_voltage(struct dev_pm_opp *opp)
> struct dev_pm_opp *tmp_opp;
> unsigned long v = 0;
>
> - opp_rcu_lockdep_assert();
> + opp_rcu_lockdep_assert(&opp->dev_opp->srcu_head.srcu);
>
> - tmp_opp = rcu_dereference(opp);
> + tmp_opp = srcu_dereference_check(opp, &opp->dev_opp->srcu_head.srcu,
> + rcu_read_lock_held());
> if (IS_ERR_OR_NULL(tmp_opp) || !tmp_opp->available)
> pr_err("%s: Invalid parameters\n", __func__);
> else
> @@ -268,9 +270,10 @@ unsigned long dev_pm_opp_get_freq(struct dev_pm_opp *opp)
> struct dev_pm_opp *tmp_opp;
> unsigned long f = 0;
>
> - opp_rcu_lockdep_assert();
> + opp_rcu_lockdep_assert(&opp->dev_opp->srcu_head.srcu);
>
> - tmp_opp = rcu_dereference(opp);
> + tmp_opp = srcu_dereference_check(opp, &opp->dev_opp->srcu_head.srcu,
> + rcu_read_lock_held());
> if (IS_ERR_OR_NULL(tmp_opp) || !tmp_opp->available)
> pr_err("%s: Invalid parameters\n", __func__);
> else
> @@ -437,7 +440,7 @@ 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();
> + opp_rcu_lockdep_assert(NULL);
>
> dev_opp = _find_device_opp(dev);
> if (IS_ERR(dev_opp)) {
> @@ -485,7 +488,7 @@ 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();
> + opp_rcu_lockdep_assert(NULL);
>
> if (!dev || !freq) {
> dev_err(dev, "%s: Invalid argument freq=%p\n", __func__, freq);
> @@ -535,7 +538,7 @@ 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();
> + opp_rcu_lockdep_assert(NULL);
>
> if (!dev || !freq) {
> dev_err(dev, "%s: Invalid argument freq=%p\n", __func__, freq);

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

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viresh