[PATCH 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 adding a NULL check before calling `fast_switch` in
`sugov_update_single_freq`.  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.

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

Wyes Karny (1):
  cpufreq/schedutil: Add fast_switch callback check

 drivers/cpufreq/amd-pstate.c     | 33 ++++++++++++++++++++++++++------
 drivers/cpufreq/cpufreq.c        | 11 +++++++++++
 include/linux/cpufreq.h          |  1 +
 kernel/sched/cpufreq_schedutil.c |  2 +-
 4 files changed, 40 insertions(+), 7 deletions(-)

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2.34.1