> Index: sys_sched.c
> ===================================================================
> RCS file: /cvsroot/src/sys/kern/sys_sched.c,v
> retrieving revision 1.9
> diff -u -p -r1.9 sys_sched.c
> --- sys_sched.c	31 Jan 2008 01:21:17 -0000	1.9
> +++ sys_sched.c	31 Jan 2008 14:38:59 -0000
> @@ -117,15 +117,29 @@ sys__sched_setparam(struct lwp *l, const
>  	pri_t pri;
>  	int error;
>  
> -	/* Available only for super-user */
> -	if (kauth_authorize_process(l->l_cred, KAUTH_PROCESS_SCHEDULER,
> -	    KAUTH_ARG(KAUTH_REQ_PROCESS_SCHEDULER_SETPARAM), NULL, NULL, NULL))
> -		return EPERM;
> +	if (SCARG(uap, pid) != 0) {
> +		/* Find the process */
> +		p = p_find(SCARG(uap, pid), PFIND_UNLOCK_FAIL);
> +		if (p == NULL)
> +			return ESRCH;
> +		mutex_enter(&p->p_smutex);
> +		mutex_exit(&proclist_lock);
> +		/* Disallow modification of system processes */
> +		if (p->p_flag & PK_SYSTEM) {
> +			mutex_exit(&p->p_smutex);
> +			return EPERM;
> +		}
> +	} else {
> +		/* Use the calling process */
> +		p = l->l_proc;
> +		mutex_enter(&p->p_smutex);
> +	}
>  
>  	/* Get the parameters from the user-space */
>  	sp = kmem_zalloc(sizeof(struct sched_param), KM_SLEEP);
>  	error = copyin(SCARG(uap, params), sp, sizeof(struct sched_param));

you should not sleep with a spin mutex held.  see mutex(9).

YAMAMOTO Takashi