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Subject[PATCH 4.14 71/71] cpufreq: governor: Ensure sufficiently large sampling intervals
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

commit 56026645e2b6f11ede34a5e6ab69d3eb56f9c8fc upstream.

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.

Fixes: aa7519af450d (cpufreq: Use transition_delay_us for legacy governors as well)
Reported-by: Andy Tang <andy.tang@nxp.com>
Reported-by: Doug Smythies <dsmythies@telus.net>
Tested-by: Andy Tang <andy.tang@nxp.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/cpufreq/cpufreq_governor.c | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)

--- 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_a
{
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 cpu
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;

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