Re: [PATCH] cpufreq/amd-pstate-ut: Disable dynamic_epp after the mode switch

[Rafael J. Wysocki]

On Sat, May 23, 2026 at 7:55 AM K Prateek Nayak <kprateek.nayak@xxxxxxx> wrote:
>
> Dan reported a possible NULL pointer dereference in amd-pstate-ut.c from
> static analysis and sure enough, running amd-pstate-ut in active mode
> with amd_dynamic_epp=enable results in a crash as a reult of the policy
> reference being set to NULL early, before disabling dynamic EPP.
>
> Kalpana also reported seeing amd-pstate-ut error out with -EBUSY for
> "amd_pstate_ut_epp" test when starting from the passive mode and
> amd_dynamic_epp=enable in the command line. The reason for the failure
> is that the command line enables dynamic_epp by default after the mode
> switch and the modifications to EPP values are blocked when running in
> dynamic EPP mode.
>
> Solution to both problems is to toggle off dynamic_epp *after* the mode
> switch when the driver grabs the policy reference again since the unit
> test is in full control of the policy after that point.
>
> The final restoration step will reset the dynamic_epp state via mode
> switch based on the initial conditions of the system.
>
> Reported-by: Kalpana Shetty <kalpana.shetty@xxxxxxx>
> Reported-by: Dan Carpenter <error27@xxxxxxxxx>
> Closes: https://lore.kernel.org/linux-pm/ahEq0CvdBX0T7_cO@stanley.mountain/
> Fixes: f9f16835d4dc ("cpufreq/amd-pstate-ut: Drop policy reference before driver switch")
> Signed-off-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
> ---
> Patches are based on:
>
>   git.kernel.org/pub/scm/linux/kernel/git/superm1/linux.git amd-pstate-fixes
>
> Sorry for the oversight on f9f16835d4dc. I've tested the fix
> exhaustively this time around on a Zen4 system with all combinations of
> driver modes and amd_dynamic_epp state and the unit test runs
> successfully under all combinations without any errors.
> ---
>  drivers/cpufreq/amd-pstate-ut.c | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/cpufreq/amd-pstate-ut.c b/drivers/cpufreq/amd-pstate-ut.c
> index 13a23dac477d..735b29f76438 100644
> --- a/drivers/cpufreq/amd-pstate-ut.c
> +++ b/drivers/cpufreq/amd-pstate-ut.c
> @@ -302,12 +302,6 @@ static int amd_pstate_ut_epp(u32 index)
>         cpufreq_cpu_put(policy);
>         policy = NULL;
>
> -       /* disable dynamic EPP before running test */
> -       if (cpudata->dynamic_epp) {
> -               pr_debug("Dynamic EPP is enabled, disabling it\n");
> -               amd_pstate_clear_dynamic_epp(policy);
> -       }
> -
>         buf = (char *)__get_free_page(GFP_KERNEL);
>         if (!buf)
>                 return -ENOMEM;
> @@ -327,6 +321,16 @@ static int amd_pstate_ut_epp(u32 index)
>         orig_policy = cpudata->policy;
>         cpudata->policy = CPUFREQ_POLICY_POWERSAVE;
>
> +       /*
> +        * Disable dynamic EPP before running test. If "orig_dynamic_epp" is
> +        * true, the  driver will do a redundant switch at the end and there
> +        * is no need for enabling it again at the end of the test.
> +        */
> +       if (cpudata->dynamic_epp) {
> +               pr_debug("Dynamic EPP is enabled, disabling it\n");
> +               amd_pstate_clear_dynamic_epp(policy);
> +       }
> +
>         for (epp = 0; epp <= U8_MAX; epp++) {
>                 u8 val;
>
>

Applied as 7.1-rc material, thanks!