linux-kernel - Re: [PATCH v2 2/3] alarmtimer: remove dead return value in clock2alarm()

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Message-ID: <CANDhNCpBpwVd2vHf8PVxxcyaxEZqof92tgF3QxYXp3c+WAwLDA@mail.gmail.com>
Date: Mon, 28 Apr 2025 16:03:01 -0700
From: John Stultz <jstultz@...gle.com>
To: Su Hui <suhui@...china.com>
Cc: tglx@...utronix.de, sboyd@...nel.org, linux-kernel@...r.kernel.org, 
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH v2 2/3] alarmtimer: remove dead return value in clock2alarm()

On Sun, Apr 27, 2025 at 4:35 AM Su Hui <suhui@...china.com> wrote:
>
> 'clockid' only can be ALARM_REALTIME and ALARM_BOOTTIME. It's impossible
> to return -1 and callers never check the value of -1.
>
> Only alarm_clock_get_timespec(), alarm_clock_get_ktime(),
> alarm_timer_create() and alarm_timer_nsleep() call clock2alarm(). These
> callers using clockid_to_kclock() to get 'struct k_clock', this ensures
> clock2alarm() never returns -1.
>
> Signed-off-by: Su Hui <suhui@...china.com>
> ---
> v2:
>  - No Change.
>  kernel/time/alarmtimer.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
> index 0ddccdff119a..e5450a77ada9 100644
> --- a/kernel/time/alarmtimer.c
> +++ b/kernel/time/alarmtimer.c
> @@ -515,9 +515,9 @@ static enum alarmtimer_type clock2alarm(clockid_t clockid)
>  {
>         if (clockid == CLOCK_REALTIME_ALARM)
>                 return ALARM_REALTIME;
> -       if (clockid == CLOCK_BOOTTIME_ALARM)
> -               return ALARM_BOOTTIME;
> -       return -1;
> +
> +       /* CLOCK_BOOTTIME_ALARM case */
> +       return ALARM_BOOTTIME;

So, I think your change is a good one, as the error case of -1 is never checked.
But it might be worth adding a WARN_ON_ONCE() if the clockid isn't
CLOCK_REALTIME_ALARM or CLOCK_BOOTTIME_ALARM, just so there aren't any
surprises if someone misuses the function.

thanks
-john