linux-kernel - Re: [PATCH] sched/fair: avoid integer overflow warning for fair_server_period

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Message-ID: <CAKfTPtDs-Y5_puGU2QYd_NatB7RQzgGQPuwfaCWXrq_8Vqw2dw@mail.gmail.com>
Date: Wed, 7 Aug 2024 12:00:35 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
	Juri Lelli <juri.lelli@...hat.com>, Arnd Bergmann <arnd@...db.de>, 
	Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, 
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	Valentin Schneider <vschneid@...hat.com>, linux-kernel@...r.kernel.org, 
	Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH] sched/fair: avoid integer overflow warning for fair_server_period_max;

Hi Arnd

On Wed, 7 Aug 2024 at 10:00, Arnd Bergmann <arnd@...nel.org> wrote:
>
> From: Arnd Bergmann <arnd@...db.de>
>
> 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@...db.de>
> ---
>  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
>