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cpufreq/amd-pstate: Grab "amd_pstate_driver_lock" when toggling dynamic_epp

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Concurrently changing driver mode and dynamic_epp with:

    echo passive > /sys/devices/system/cpu/amd_pstate/status&
    echo disable > /sys/devices/system/cpu/amd_pstate/dynamic_epp&

hits the WARN_ON_ONCE() in static_key_disable_cpuslocked() and hangs the
system since both sysfs writes are trying to do
amd_pstate_change_driver_mode() without any synchronization.

Grab the "amd_pstate_driver_lock" mutex when modifying "dynamic_epp" to
prevent the two paths from racing with each other. Add a lockdep
assertion for "amd_pstate_driver_lock" in
amd_pstate_change_driver_mode() to formalize the dependency.

Since "cppc_mode" is stable under "amd_pstate_driver_lock", only reload
the driver when in "AMD_PSTATE_ACTIVE" mode and reject all writes when
in passive or guided mode, or if the driver is not loaded, since only
active mode operates on EPP.

Fixes: e30ca6dd53 ("cpufreq/amd-pstate: Add dynamic energy performance preference")
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://lore.kernel.org/r/20260508051748.10484-2-kprateek.nayak@amd.com
Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
This commit is contained in:
K Prateek Nayak 2026-05-08 05:17:43 +00:00 committed by Mario Limonciello (AMD)
parent 7fd2df204f
commit 9228169d2a
1 changed files with 9 additions and 0 deletions
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9
drivers/cpufreq/amd-pstate.c
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@ -1707,6 +1707,8 @@ static int amd_pstate_change_driver_mode(int mode)
{
int ret;
lockdep_assert_held(&amd_pstate_driver_lock);
ret = amd_pstate_unregister_driver(0);
if (ret)
return ret;
@ -1821,6 +1823,13 @@ static ssize_t dynamic_epp_store(struct device *a, struct device_attribute *b,
if (ret)
return ret;
guard(mutex)(&amd_pstate_driver_lock);
if (cppc_state != AMD_PSTATE_ACTIVE) {
pr_debug("dynamic_epp can only be toggled in active mode\n");
return -EINVAL;
}
if (dynamic_epp == enabled)
return -EINVAL;