cpufreq: prevent NULL dereference in cpufreq_online()

Ensure cpufreq_driver->set_boost is non-NULL before using it in
cpufreq_online() to prevent a potential NULL pointer dereference.

Reported-by: Gautam Menghani <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]/
Fixes: dd016f3 ("cpufreq: Introduce a more generic way to set default per-policy boost flag")
Suggested-by: Viresh Kumar <[email protected]>
Signed-off-by: Aboorva Devarajan <[email protected]>
Link: https://patch.msgid.link/[email protected]
[ rjw: Minor edits in the subject and changelog ]
Signed-off-by: Rafael J. Wysocki <[email protected]>

Author: AboorvaDevarajan

drivers/cpufreq/cpufreq.c

@@ -1571,7 +1571,8 @@ static int cpufreq_online(unsigned int cpu)
 		policy->cdev = of_cpufreq_cooling_register(policy);
 
 	/* Let the per-policy boost flag mirror the cpufreq_driver boost during init */
-	if (policy->boost_enabled != cpufreq_boost_enabled()) {
+	if (cpufreq_driver->set_boost &&
+	    policy->boost_enabled != cpufreq_boost_enabled()) {
 		policy->boost_enabled = cpufreq_boost_enabled();
 		ret = cpufreq_driver->set_boost(policy, policy->boost_enabled);
 		if (ret) {