linux-kernel - Re: [RFC][PATCH] SCHED

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Date:	Tue, 29 Sep 2009 20:15:37 +0200
From:	roel kluin <roel.kluin@...il.com>
To:	Raistlin <raistlin@...ux.it>
Cc:	Linus Walleij <linus.ml.walleij@...il.com>,
	Peter Zijlstra <peterz@...radead.org>, claudio@...dence.eu.com,
	michael@...dence.eu.com, mingo@...e.hu,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	johan.eker@...csson.com, p.faure@...tech.ch,
	Fabio Checconi <fabio@...dalf.sssup.it>,
	Dhaval Giani <dhaval.giani@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tommaso Cucinotta <tommaso.cucinotta@...up.it>
Subject: Re: [RFC][PATCH] SCHED_EDF scheduling class

>  static int __sched_setscheduler(struct task_struct *p, int policy,
> -                               struct sched_param *param, bool user)
> +                               struct sched_param *param,
> +                               struct sched_param_ex *param_ex,
> +                               bool user)
...

> @@ -6200,6 +6364,13 @@ recheck:
>            (p->mm && param->sched_priority > MAX_USER_RT_PRIO-1) ||
>            (!p->mm && param->sched_priority > MAX_RT_PRIO-1))
>                return -EINVAL;
> +       if (edf_policy(policy) && param_ex->sched_priority != 0)
> +               return -EINVAL;
> +       if (edf_policy(policy) && (param_ex == NULL ||
> +           timespec_to_ns(&param_ex->sched_period) == 0 ||
> +           timespec_to_ns(&param_ex->sched_period) <
> +           timespec_to_ns(&param_ex->sched_runtime)))
> +               return -EINVAL;

shouldn't the NULL test be moved upwards, to prevent a dereference of
a NULL pointer? Also I notice that `timespec_to_ns(&param_ex->sched_period)'
is called twice, maybe gcc does this but can't we do something like

        if (edf_policy(policy)) {
                if (param_ex == NULL || param_ex->sched_priority != 0)
                        return -EINVAL;
                s64 psp = timespec_to_ns(&param_ex->sched_period);
                if (psp == 0 || psp < timespec_to_ns(&param_ex->sched_runtime))
                        return -EINVAL;
        }

Roel
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