[PATCH v2 0/2] cpufreq/schedutil: Fix null pointer dereference in sugov_update_single_freq

From: Wyes Karny
Date: Tue May 09 2023 - 14:05:36 EST

Currently, amd_pstate only uses `adjust_perf` and `target` callback
functions to get the frequency/effective utilization data from scaling
governors. Schedutil generally avoids calling `target` and `fast_switch`
functions if `adjust_perf` function pointer is set for the driver. But in
some rare cases, schedutil tries to call `fast_switch` function even the
function pointer is not set. This happens when frequency invariance is
turned off. When frequency invariance is turned off schedutil falls
back to `sugov_update_single_freq` which currently relies on the
`fast_switch` callback.

Currently, frequency invariance is turned off when any anomaly is
detected with aperf/mperf readings. Which triggers this problem.

Fix this by disabling `fast_switch_enabled` flag if `fast_switch`
callback is not set and removing `fast_switch_enabled` flag dependency
for adjust_perf callback. But this will force schedutil to take a slower
path to update frequency. Therefore to fix this add fast_switch
function on amd_pstate to take advantage of fast frequency update.

v1 -> v2
- Remove fast_switch_enabled flag dependency for adjust_perf callback

v1: https://lore.kernel.org/linux-pm/20230410095045.14872-1-wyes.karny@xxxxxxx/

Gautham R. Shenoy (1):
amd_pstate: Add ->fast_switch() callback

Wyes Karny (1):
cpufreq/schedutil: Remove fast_switch_possible flag if driver doesn't
set fast_switch

drivers/cpufreq/amd-pstate.c | 46 +++++++++++++++++++++++++-------
drivers/cpufreq/cpufreq.c | 20 +++++++++++++-
drivers/cpufreq/intel_pstate.c | 3 +--
include/linux/cpufreq.h | 1 +
kernel/sched/cpufreq_schedutil.c | 2 +-
5 files changed, 59 insertions(+), 13 deletions(-)