cpufreq: CPPC: Fix wrong return value in cppc_get_cpu_cost()

cppc_get_cpu_cost() return 0 if the policy is NULL. Then in
em_compute_costs(), the later zero check for cost is not valid
as cost is uninitialized. As Quentin pointed out, kernel energy model
core check the return value of get_cost() first, so if the callback
failed it should tell the core. Return -EINVAL to fix it.

Fixes: 1a1374b ("cpufreq: CPPC: Fix possible null-ptr-deref for cppc_get_cpu_cost()")
Reported-by: Dan Carpenter <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Jinjie Ruan <[email protected]>
Suggested-by: Quentin Perret <[email protected]>
Signed-off-by: Viresh Kumar <[email protected]>

Author: Jinjie Ruan

drivers/cpufreq/cppc_cpufreq.c

@@ -475,7 +475,7 @@ static int cppc_get_cpu_cost(struct device *cpu_dev, unsigned long KHz,
 
 	policy = cpufreq_cpu_get_raw(cpu_dev->id);
 	if (!policy)
-		return 0;
+		return -EINVAL;
 
 	cpu_data = policy->driver_data;
 	perf_caps = &cpu_data->perf_caps;