[PATCH] cpufreq: schedutil: Fix rate limit overflow

[Hui Su]

rate_limit_us is unsigned int. On 32-bit systems, multiplying it by
NSEC_PER_USEC is therefore carried out in 32-bit arithmetic before
the result is assigned to freq_update_delay_ns.

For example, writing 4294968 to rate_limit_us wraps the delay from
4294968000 ns to 704 ns. This makes schedutil update far more often
than configured.

Add sugov_update_rate_limit_us() to widen the value to u64 before
converting units. Use it when updating the tunable through sysfs and
when starting the governor, so both paths set the same valid delay.

Fixes: 9bdcb44e391d ("cpufreq: schedutil: New governor based on scheduler utilization data")
Signed-off-by: Hui Su <sh_def@xxxxxxx>

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index dff4ee04694c2b90301ed0fa158a509a3423cee1..8bf7a2c34b9f200d8f5776205ea2a7f495e04e69 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -61,6 +61,12 @@ static DEFINE_PER_CPU(struct sugov_cpu, sugov_cpu);
 
 /************************ Governor internals ***********************/
 
+static void sugov_update_rate_limit_us(struct sugov_policy *sg_policy)
+{
+	sg_policy->freq_update_delay_ns =
+		(u64)sg_policy->tunables->rate_limit_us * NSEC_PER_USEC;
+}
+
 static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time)
 {
 	s64 delta_ns;
@@ -606,7 +612,7 @@ rate_limit_us_store(struct gov_attr_set *attr_set, const char *buf, size_t count
 	tunables->rate_limit_us = rate_limit_us;
 
 	list_for_each_entry(sg_policy, &attr_set->policy_list, tunables_hook)
-		sg_policy->freq_update_delay_ns = rate_limit_us * NSEC_PER_USEC;
+		sugov_update_rate_limit_us(sg_policy);
 
 	return count;
 }
@@ -848,7 +854,7 @@ static int sugov_start(struct cpufreq_policy *policy)
 	void (*uu)(struct update_util_data *data, u64 time, unsigned int flags);
 	unsigned int cpu;
 
-	sg_policy->freq_update_delay_ns	= sg_policy->tunables->rate_limit_us * NSEC_PER_USEC;
+	sugov_update_rate_limit_us(sg_policy);
 	sg_policy->last_freq_update_time	= 0;
 	sg_policy->next_freq			= 0;
 	sg_policy->work_in_progress		= false;
-- 
2.43.0