linux-kernel - Re: [PATCH v2] cpufreq: amd-pstate: fix kernel hang issue while amd-pstate unregistering

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Message-ID: <CAJZ5v0j1ioh5aSRMB8DTvtKzX22n3AmLfgmDmbKCYQMAoJx6aQ@mail.gmail.com>
Date:   Tue, 10 Jan 2023 13:57:30 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Perry Yuan <perry.yuan@....com>
Cc:     rafael.j.wysocki@...el.com, Mario.Limonciello@....com,
        ray.huang@....com, viresh.kumar@...aro.org, Deepak.Sharma@....com,
        Nathan.Fontenot@....com, Alexander.Deucher@....com,
        Shimmer.Huang@....com, Xiaojian.Du@....com, Li.Meng@....com,
        wyes.karny@....com, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] cpufreq: amd-pstate: fix kernel hang issue while
 amd-pstate unregistering

On Tue, Jan 10, 2023 at 1:50 PM Perry Yuan <perry.yuan@....com> wrote:
>
> In the amd_pstate_adjust_perf(), there is one cpufreq_cpu_get() call to
> increase increments the kobject reference count of policy and make it as
> busy. Therefore, a corresponding call to cpufreq_cpu_put() is needed to
> decrement the kobject reference count back, it will resolve the kernel
> hang issue when unregistering the amd-pstate driver and register the
> `amd_pstate_epp` driver instance.
>
> Acked-by: Huang Rui <ray.huang@....com>
> Reviewed-by: Mario Limonciello <mario.limonciello@....com>
> Signed-off-by: Perry Yuan <perry.yuan@....com>
> Tested-by: Wyes Karny <wyes.karny@....com>
> Cc: stable@...r.kernel.org

Can you provide a Fixes tag, please?

Also, what's the difference between this and the previous version?

> ---
>  drivers/cpufreq/amd-pstate.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 204e39006dda..c17bd845f5fc 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -307,6 +307,7 @@ static void amd_pstate_adjust_perf(unsigned int cpu,
>                 max_perf = min_perf;
>
>         amd_pstate_update(cpudata, min_perf, des_perf, max_perf, true);
> +       cpufreq_cpu_put(policy);
>  }
>
>  static int amd_get_min_freq(struct amd_cpudata *cpudata)
> --
> 2.34.1
>