linux-kernel - Re: [BUG] sched_setattr() SCHED

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Message-ID: <20140513104307.GZ30445@twins.programming.kicks-ass.net>
Date:	Tue, 13 May 2014 12:43:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Juri Lelli <juri.lelli@...il.com>
Cc:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	Dario Faggioli <raistlin@...ux.it>,
	Ingo Molnar <mingo@...e.hu>,
	lkml <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: [BUG] sched_setattr() SCHED_DEADLINE hangs system

On Tue, May 13, 2014 at 11:57:49AM +0200, Juri Lelli wrote:
>  static bool
>  __checkparam_dl(const struct sched_attr *attr)
>  {
>  	return attr && attr->sched_deadline != 0 &&
>  		(attr->sched_period == 0 ||
> -		(s64)(attr->sched_period   - attr->sched_deadline) >= 0) &&
> -		(s64)(attr->sched_deadline - attr->sched_runtime ) >= 0  &&
> -		attr->sched_runtime >= (2 << (DL_SCALE - 1));
> +		(attr->sched_period >= attr->sched_deadline)) &&
> +		(attr->sched_deadline >= attr->sched_runtime) &&
> +		attr->sched_runtime >= (1ULL << DL_SCALE) &&
> +		(attr->sched_deadline < (1ULL << 63) &&
> +		attr->sched_period < (1ULL << 63));
>  }

Could we maybe rewrite that function to look less like a ioccc.org
submission?

static bool
__checkparam_dl(const struct sched_attr *attr)
{
	if (!attr) /* possible at all? */
		return false;

	/* runtime <= deadline <= period */
	if (attr->sched_period   < attr->sched_deadline ||
	    attr->sched_deadline < attr->sched_runtime)
		return false;

	/*
	 * Since we truncate DL_SCALE bits make sure we're at least that big,
	 * if runtime > (1 << DL_SCALE), so must the others be per the above
	 */
	if (attr->sched_runtime <= (1ULL << DL_SCALE))
		return false;

	/*
	 * Since we use the MSB for wrap-around and sign issues, make
	 * sure its not set, if period < 2^63, so must the others be.
	 */
	if (attr->sched_period & (1ULL << 63))
		return false;

	return true;
}

Did I miss anything?

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