On Wednesday, June 19, 2013 02:23:07 PM Viresh Kumar wrote:
> Whenever we are changing frequency of a cpu, we are calling PRECHANGE and
> POSTCHANGE notifiers. They must be serialized. i.e. PRECHANGE or POSTCHANGE
> shouldn't be called twice contiguously.
>
> This can happen due to bugs in users of __cpufreq_driver_target() or actual
> cpufreq drivers who are sending these notifiers.
>
> This patch adds some protection against this. Now, we keep track of the last
> transaction and see if something went wrong.
>
> Signed-off-by: Viresh Kumar <viresh.ku...@linaro.org>
> ---
> drivers/cpufreq/cpufreq.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 2d53f47..92cb8b3 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -107,6 +107,9 @@ static void handle_update(struct work_struct *work);
> static BLOCKING_NOTIFIER_HEAD(cpufreq_policy_notifier_list);
> static struct srcu_notifier_head cpufreq_transition_notifier_list;
>
> +/* Tracks status of transition */
> +static int transition_ongoing;
> +
> static bool init_cpufreq_transition_notifier_list_called;
> static int __init init_cpufreq_transition_notifier_list(void)
> {
> @@ -264,6 +267,8 @@ void __cpufreq_notify_transition(struct cpufreq_policy
> *policy,
> switch (state) {
>
> case CPUFREQ_PRECHANGE:
> + WARN_ON(transition_ongoing++);
> +
> /* detect if the driver reported a value as "old frequency"
> * which is not equal to what the cpufreq core thinks is
> * "old frequency".
> @@ -283,6 +288,8 @@ void __cpufreq_notify_transition(struct cpufreq_policy
> *policy,
> break;
>
> case CPUFREQ_POSTCHANGE:
> + WARN_ON(!transition_ongoing--);
Shouldn't we try to avoid going into the negative range here?
> +
> adjust_jiffies(CPUFREQ_POSTCHANGE, freqs);
> pr_debug("FREQ: %lu - CPU: %lu", (unsigned long)freqs->new,
> (unsigned long)freqs->cpu);
> @@ -1458,6 +1465,8 @@ int __cpufreq_driver_target(struct cpufreq_policy
> *policy,
>
> if (cpufreq_disabled())
> return -ENODEV;
> + if (transition_ongoing)
> + return -EBUSY;
>
> /* Make sure that target_freq is within supported range */
> if (target_freq > policy->max)
>
Rafael
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
