linux-kernel - Re: [PATCH v2] sys_prctl(): remove unsigned comparision with less than zero

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Date:   Wed, 24 Jul 2019 19:14:48 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Yang Xu <xuyang2018.jy@...fujitsu.com>
Cc:     <gorcunov@...il.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] sys_prctl(): remove unsigned comparision with less
 than zero

On Wed, 24 Jul 2019 10:11:48 +0800 Yang Xu <xuyang2018.jy@...fujitsu.com> wrote:

> Currently, when calling prctl(PR_SET_TIMERSLACK, arg2), arg2 is an
> unsigned long value, arg2 will never < 0. Negative judgment is
> meaningless, so remove it.
> 
> ...
>
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -2372,7 +2372,7 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>  			error = current->timer_slack_ns;
>  		break;
>  	case PR_SET_TIMERSLACK:
> -		if (arg2 <= 0)
> +		if (arg2 == 0)
>  			current->timer_slack_ns =
>  					current->default_timer_slack_ns;

A number of years ago Linus expressed approval of such comparisons with
unsigned quantities.  He felt that it improves readability a little -
the reader doesn't have to scroll back and check the type.