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

[Wyes Karny]

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.

Changelog:
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(-)

-- 
2.34.1