[PATCH] cpufreq/amd-pstate: handle missing policy in dynamic EPP callbacks

[EDAMAMEX <edame8080@gmail.com>]

cpufreq_cpu_get() returns NULL when no cpufreq policy is associated with
the requested CPU, for example because the CPU is offline or the policy
has already been torn down.  Both amd_pstate_power_supply_notifier() and
amd_pstate_profile_set() acquire a policy via cpufreq_cpu_get() and then
pass that pointer to amd_pstate_get_balanced_epp() and
amd_pstate_set_epp(), which dereference it unconditionally.  A racing
CPU hotplug or driver teardown can therefore lead to a NULL pointer
dereference on either of these dynamic EPP paths.

The third cpufreq_cpu_get() caller in this file, amd_pstate_verify(),
already handles the NULL case.  Bring the two new callers in line with
that pattern: return NOTIFY_OK from the power-supply notifier (matching
the other "nothing to do" exits) and -ENODEV from amd_pstate_profile_set()
(the usual cpufreq error for a missing CPU policy).

Found by code inspection; not tested on hardware.

Fixes: e30ca6dd5345 ("cpufreq/amd-pstate: Add dynamic energy performance preference")
Fixes: 798c47593cca ("cpufreq/amd-pstate: Add support for platform profile class")
Signed-off-by: EDAMAMEX <edame8080@gmail.com>
---
 drivers/cpufreq/amd-pstate.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 453084c67..f659a54c7 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -1183,6 +1183,9 @@ static int amd_pstate_power_supply_notifier(struct notifier_block *nb,
 	if (cpudata->current_profile != PLATFORM_PROFILE_BALANCED)
 		return 0;
 
+	if (!policy)
+		return NOTIFY_OK;
+
 	epp = amd_pstate_get_balanced_epp(policy);
 
 	ret = amd_pstate_set_epp(policy, epp);
@@ -1218,6 +1221,9 @@ static int amd_pstate_profile_set(struct device *dev,
 	struct cpufreq_policy *policy __free(put_cpufreq_policy) = cpufreq_cpu_get(cpudata->cpu);
 	int ret;
 
+	if (!policy)
+		return -ENODEV;
+
 	switch (profile) {
 	case PLATFORM_PROFILE_LOW_POWER:
 		ret = amd_pstate_set_epp(policy, AMD_CPPC_EPP_POWERSAVE);
-- 
2.43.0