linux-kernel - Re: [PATCH] PM: QoS: Add check to make sure CPU latency is non-negative

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Message-ID: <CAJZ5v0jYYN2MpqYW35N+-jzqpfY0ATGfUEwhgY1O3WXk9QoSRg@mail.gmail.com>
Date:   Tue, 22 Aug 2023 21:39:09 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Clive Lin <clive.lin@...iatek.com>
Cc:     rafael@...nel.org, pavel@....cz, len.brown@...el.com,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        chung-kai.yang@...iatek.com, ccj.yeh@...iatek.com,
        ching-hao.hsu@...iatek.com
Subject: Re: [PATCH] PM: QoS: Add check to make sure CPU latency is non-negative

On Mon, Jul 31, 2023 at 8:04 AM Clive Lin <clive.lin@...iatek.com> wrote:
>
> CPU latency should never be negative, which will be incorrectly high
> when converted to unsigned data type. Commit 8d36694245f2 ("PM: QoS:
> Add check to make sure CPU freq is non-negative") makes sure CPU freq
> is non-negative to fix incorrect behavior in freq_qos. Adding a check
> to make sure CPU latency is non-negative can prevent this problem
> from happening in cpu_latency_qos.
>
> Signed-off-by: Clive Lin <clive.lin@...iatek.com>
> ---
>  kernel/power/qos.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/power/qos.c b/kernel/power/qos.c
> index 782d3b41c1f3..4244b069442e 100644
> --- a/kernel/power/qos.c
> +++ b/kernel/power/qos.c
> @@ -220,6 +220,11 @@ static struct pm_qos_constraints cpu_latency_constraints = {
>         .type = PM_QOS_MIN,
>  };
>
> +static inline bool cpu_latency_qos_value_invalid(s32 value)
> +{
> +       return value < 0 && value != PM_QOS_DEFAULT_VALUE;
> +}
> +
>  /**
>   * cpu_latency_qos_limit - Return current system-wide CPU latency QoS limit.
>   */
> @@ -263,7 +268,7 @@ static void cpu_latency_qos_apply(struct pm_qos_request *req,
>   */
>  void cpu_latency_qos_add_request(struct pm_qos_request *req, s32 value)
>  {
> -       if (!req)
> +       if (!req || cpu_latency_qos_value_invalid(value))
>                 return;
>
>         if (cpu_latency_qos_request_active(req)) {
> @@ -289,7 +294,7 @@ EXPORT_SYMBOL_GPL(cpu_latency_qos_add_request);
>   */
>  void cpu_latency_qos_update_request(struct pm_qos_request *req, s32 new_value)
>  {
> -       if (!req)
> +       if (!req || cpu_latency_qos_value_invalid(new_value))
>                 return;
>
>         if (!cpu_latency_qos_request_active(req)) {
> --

Applied (with some edits in the changelog) as 6.6 material, thanks!