Re: [PATCH] sched/fair: avoid integer overflow warning for fair_server_period_max;

[Vincent Guittot]

Hi Arnd

On Wed, 7 Aug 2024 at 10:00, Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
>
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> The clalculation of fair_server_period_max includes an integer overflow:
>
> In file included from kernel/sched/build_utility.c:72:
> kernel/sched/debug.c:341:57: error: integer overflow in expression of type 'long int' results in '-100663296' [-Werror=overflow]
>   341 | static unsigned long fair_server_period_max = (1 << 22) * NSEC_PER_USEC; /* ~4 seconds */
>
> Avoids this by using an unsigned constant to start with.

Dan sent something similar
https://lore.kernel.org/lkml/a936b991-e464-4bdf-94ab-08e25d364986@stanley.mountain/

>
> Fixes: d741f297bcea ("sched/fair: Fair server interface")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
>  kernel/sched/debug.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 0148bc65d39c..242e7f264a0b 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -338,7 +338,7 @@ enum dl_param {
>         DL_PERIOD,
>  };
>
> -static unsigned long fair_server_period_max = (1 << 22) * NSEC_PER_USEC; /* ~4 seconds */
> +static unsigned long fair_server_period_max = (1u << 22) * NSEC_PER_USEC; /* ~4 seconds */
>  static unsigned long fair_server_period_min = (100) * NSEC_PER_USEC;     /* 100 us */
>
>  static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubuf,
> --
> 2.39.2
>