linux-kernel - Re: [PATCH] sched/deadline: Don't use dubious signed bitfields

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Date:   Fri, 13 Oct 2017 09:36:06 +0200
From:   Luca Abeni <luca.abeni@...tannapisa.it>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] sched/deadline: Don't use dubious signed bitfields

Hi,

On Fri, 13 Oct 2017 10:01:22 +0300
Dan Carpenter <dan.carpenter@...cle.com> wrote:

> It doesn't cause a run-time bug, but these bitfields should be unsigned.
> When it's signed ->dl_throttled is set to either 0 or -1, instead of
> 0 and 1 as expected.  The sched.h file is included into tons of places
> so Sparse generates a flood of warnings like this:
> 
> ./include/linux/sched.h:477:54: error: dubious one-bit signed bitfield
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>

I did not notice any issue when testing, but if "unsigned int" is the
common practice for bitfields, I agree with the change.

Reviewed-by: Luca Abeni <luca.abeni@...tannapisa.it>


			Thanks,
				Luca
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 0f897dfc195e..105eaff8a5e7 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -474,10 +474,10 @@ struct sched_dl_entity {
>  	 * conditions between the inactive timer handler and the wakeup
>  	 * code.
>  	 */
> -	int				dl_throttled      : 1;
> -	int				dl_boosted        : 1;
> -	int				dl_yielded        : 1;
> -	int				dl_non_contending : 1;
> +	unsigned int			dl_throttled      : 1;
> +	unsigned int			dl_boosted        : 1;
> +	unsigned int			dl_yielded        : 1;
> +	unsigned int			dl_non_contending : 1;
>  
>  	/*
>  	 * Bandwidth enforcement timer. Each -deadline task has its