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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Fri, 15 Jul 2022 13:50:15 +0200
Message-ID: <CAJZ5v0hBTGJ3K5VMnef22-6yEU7rDn1wMBmgqeu41wKQyydNgA@mail.gmail.com>
Subject: Re: [PATCH v3]PM: QoS: Add check to make sure CPU freq is non-negative
To:     Shivnandan Kumar <quic_kshivnan@quicinc.com>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
        Linux PM <linux-pm@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Fri, Jul 15, 2022 at 6:10 AM Shivnandan Kumar
<quic_kshivnan@quicinc.com> wrote:
>
>         CPU frequency should never be negative.
>         If some client driver calls freq_qos_update_request with
>         negative value which will be very high in absolute terms,
>         then qos driver set max CPU freq at fmax as it consider
>         it's absolute value but it will add plist node with negative
>         priority. plist node has priority from INT_MIN (highest)
>         to INT_MAX(lowest). Once priority is set as negative,
>         another client will not be able to reduce CPU frequency.
>         Adding check to make sure CPU freq is non-negative will
>         fix this problem.
>
> Signed-off-by: Shivnandan Kumar <quic_kshivnan@quicinc.com>
> ---
> v2->v3
>         -changed commit text
> v1->v2
>         -addressed comments from Rafael
>         -changed commit text accordingly
>  kernel/power/qos.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/power/qos.c b/kernel/power/qos.c
> index ec7e1e85923e..27e6596f287a 100644
> --- a/kernel/power/qos.c
> +++ b/kernel/power/qos.c
> @@ -531,7 +531,7 @@ int freq_qos_add_request(struct freq_constraints *qos,
>  {
>         int ret;
>
> -       if (IS_ERR_OR_NULL(qos) || !req)
> +       if (IS_ERR_OR_NULL(qos) || !req || value < FREQ_QOS_MIN_DEFAULT_VALUE)

Why not just put 0 in there directly instead of FREQ_QOS_MIN_DEFAULT_VALUE?

As is, it is somewhat confusing (and same below).

>                 return -EINVAL;
>
>         if (WARN(freq_qos_request_active(req),
> @@ -563,7 +563,7 @@ EXPORT_SYMBOL_GPL(freq_qos_add_request);
>   */
>  int freq_qos_update_request(struct freq_qos_request *req, s32 new_value)
>  {
> -       if (!req)
> +       if (!req || new_value < FREQ_QOS_MIN_DEFAULT_VALUE)
>                 return -EINVAL;
>
>         if (WARN(!freq_qos_request_active(req),
> --
> 2.25.1
>