linux-kernel - Re: [PATCH] cpufreq: Fix policy->freq_table is NULL in __cpufreq_driver

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Date:   Wed, 29 Mar 2023 16:21:38 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Yajun Deng <yajun.deng@...ux.dev>
Cc:     rafael@...nel.org, viresh.kumar@...aro.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq: Fix policy->freq_table is NULL in __cpufreq_driver_target()

On Wed, Mar 29, 2023 at 3:36 PM Yajun Deng <yajun.deng@...ux.dev> wrote:
>
> __resolve_freq() may be return target_freq if policy->freq_table is
> NULL. In this case, it should return -EINVAL before __target_index().

Even so, __target_index() itself doesn't dereference freq_table
AFAICS, so arguably the driver should be prepared to deal with a NULL
freq_table which comes from it after all.

Or, if you want to argue that drivers providing ->target_index() must
also provide freq_table that is not NULL, a check to that effect needs
to be done at the driver registration time IMO.

> Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
> ---
>  drivers/cpufreq/cpufreq.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index c0e5be0fe2d6..308a3df1a940 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2299,7 +2299,7 @@ int __cpufreq_driver_target(struct cpufreq_policy *policy,
>                 return cpufreq_driver->target(policy, target_freq, relation);
>         }
>
> -       if (!cpufreq_driver->target_index)
> +       if (!cpufreq_driver->target_index || !policy->freq_table)
>                 return -EINVAL;
>
>         return __target_index(policy, policy->cached_resolved_idx);
> --