On Monday, January 29, 2018 8:21:23 AM CET Viresh Kumar wrote:
> From: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx>
>
> [ Upstream commit 56026645e2b6f11ede34a5e6ab69d3eb56f9c8fc ]
>
> After commit aa7519af450d (cpufreq: Use transition_delay_us for legacy
> governors as well) the sampling_rate field of struct dbs_data may be
> less than the tick period which causes dbs_update() to produce
> incorrect results, so make the code ensure that the value of that
> field will always be sufficiently large.
>
> Cc: 4.14 <stable@xxxxxxxxxxxxxxx> # 4.14
> Fixes: aa7519af450d (cpufreq: Use transition_delay_us for legacy governors as well)
> Reported-by: Andy Tang <andy.tang@xxxxxxx>
> Reported-by: Doug Smythies <dsmythies@xxxxxxxxx>
> Tested-by: Andy Tang <andy.tang@xxxxxxx>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> ---
> drivers/cpufreq/cpufreq_governor.c | 19 ++++++++++++++++---
> 1 file changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
> index 58d4f4e1ad6a..ca38229b045a 100644
> --- a/drivers/cpufreq/cpufreq_governor.c
> +++ b/drivers/cpufreq/cpufreq_governor.c
> @@ -22,6 +22,8 @@
>
> #include "cpufreq_governor.h"
>
> +#define CPUFREQ_DBS_MIN_SAMPLING_INTERVAL (2 * TICK_NSEC / NSEC_PER_USEC)
> +
> static DEFINE_PER_CPU(struct cpu_dbs_info, cpu_dbs);
>
> static DEFINE_MUTEX(gov_dbs_data_mutex);
> @@ -47,11 +49,15 @@ ssize_t store_sampling_rate(struct gov_attr_set *attr_set, const char *buf,
> {
> struct dbs_data *dbs_data = to_dbs_data(attr_set);
> struct policy_dbs_info *policy_dbs;
> + unsigned int sampling_interval;
> int ret;
> - ret = sscanf(buf, "%u", &dbs_data->sampling_rate);
> - if (ret != 1)
> +
> + ret = sscanf(buf, "%u", &sampling_interval);
> + if (ret != 1 || sampling_interval < CPUFREQ_DBS_MIN_SAMPLING_INTERVAL)
> return -EINVAL;
>
> + dbs_data->sampling_rate = sampling_interval;
> +
> /*
> * We are operating under dbs_data->mutex and so the list and its
> * entries can't be freed concurrently.
> @@ -430,7 +436,14 @@ int cpufreq_dbs_governor_init(struct cpufreq_policy *policy)
> if (ret)
> goto free_policy_dbs_info;
>
> - dbs_data->sampling_rate = cpufreq_policy_transition_delay_us(policy);
> + /*
> + * The sampling interval should not be less than the transition latency
> + * of the CPU and it also cannot be too small for dbs_update() to work
> + * correctly.
> + */
> + dbs_data->sampling_rate = max_t(unsigned int,
> + CPUFREQ_DBS_MIN_SAMPLING_INTERVAL,
> + cpufreq_policy_transition_delay_us(policy));
>
> if (!have_governor_per_policy())
> gov->gdbs_data = dbs_data;
>
Right, thanks for pushing this to -stable!