xref: /src/sys/kern/sys_sched.c

/*	$NetBSD: sys_sched.c,v 1.50 2023/04/09 09:18:09 riastradh Exp $	*/

/*
 * Copyright (c) 2008, 2011 Mindaugas Rasiukevicius <rmind at NetBSD org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * System calls relating to the scheduler.
 *
 * Lock order:
 *
 *	cpu_lock ->
 *	    proc_lock ->
 *		proc_t::p_lock ->
 *		    lwp_t::lwp_lock
 *
 * TODO:
 *  - Handle pthread_setschedprio() as defined by POSIX;
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: sys_sched.c,v 1.50 2023/04/09 09:18:09 riastradh Exp $");

#include <sys/param.h>

#include <sys/cpu.h>
#include <sys/kauth.h>
#include <sys/kmem.h>
#include <sys/lwp.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/pset.h>
#include <sys/sched.h>
#include <sys/syscallargs.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/types.h>
#include <sys/unistd.h>

static struct sysctllog *sched_sysctl_log;
static kauth_listener_t sched_listener;

/*
 * Convert user priority or the in-kernel priority or convert the current
 * priority to the appropriate range according to the policy change.
 */
static pri_t
convert_pri(lwp_t *l, int policy, pri_t pri)
{

	/* Convert user priority to the in-kernel */
	if (pri != PRI_NONE) {
		/* Only for real-time threads */
		KASSERT(pri >= SCHED_PRI_MIN);
		KASSERT(pri <= SCHED_PRI_MAX);
		KASSERT(policy != SCHED_OTHER);
		return PRI_USER_RT + pri;
	}

	/* Neither policy, nor priority change */
	if (l->l_class == policy)
		return l->l_priority;

	/* Time-sharing -> real-time */
	if (l->l_class == SCHED_OTHER) {
		KASSERT(policy == SCHED_FIFO || policy == SCHED_RR);
		return PRI_USER_RT;
	}

	/* Real-time -> time-sharing */
	if (policy == SCHED_OTHER) {
		KASSERT(l->l_class == SCHED_FIFO || l->l_class == SCHED_RR);
		/*
		 * this is a bit arbitrary because the priority is dynamic
		 * for SCHED_OTHER threads and will likely be changed by
		 * the scheduler soon anyway.
		 */
		return l->l_priority - PRI_USER_RT;
	}

	/* Real-time -> real-time */
	return l->l_priority;
}

int
do_sched_setparam(pid_t pid, lwpid_t lid, int policy,
    const struct sched_param *params)
{
	struct proc *p;
	struct lwp *t;
	pri_t pri;
	u_int lcnt;
	int error;

	error = 0;

	pri = params->sched_priority;

	/* If no parameters specified, just return (this should not happen) */
	if (pri == PRI_NONE && policy == SCHED_NONE)
		return 0;

	/* Validate scheduling class */
	if (policy != SCHED_NONE && (policy < SCHED_OTHER || policy > SCHED_RR))
		return EINVAL;

	/* Validate priority */
	if (pri != PRI_NONE && (pri < SCHED_PRI_MIN || pri > SCHED_PRI_MAX))
		return EINVAL;

	if (pid != 0) {
		/* Find the process */
		mutex_enter(&proc_lock);
		p = proc_find(pid);
		if (p == NULL) {
			mutex_exit(&proc_lock);
			return ESRCH;
		}
		mutex_enter(p->p_lock);
		mutex_exit(&proc_lock);
		/* Disallow modification of system processes */
		if ((p->p_flag & PK_SYSTEM) != 0) {
			mutex_exit(p->p_lock);
			return EPERM;
		}
	} else {
		/* Use the calling process */
		p = curlwp->l_proc;
		mutex_enter(p->p_lock);
	}

	/* Find the LWP(s) */
	lcnt = 0;
	LIST_FOREACH(t, &p->p_lwps, l_sibling) {
		pri_t kpri;
		int lpolicy;

		if (lid && lid != t->l_lid)
			continue;

		lcnt++;
		lwp_lock(t);
		lpolicy = (policy == SCHED_NONE) ? t->l_class : policy;

		/* Disallow setting of priority for SCHED_OTHER threads */
		if (lpolicy == SCHED_OTHER && pri != PRI_NONE) {
			lwp_unlock(t);
			error = EINVAL;
			break;
		}

		/* Convert priority, if needed */
		kpri = convert_pri(t, lpolicy, pri);

		/* Check the permission */
		error = kauth_authorize_process(kauth_cred_get(),
		    KAUTH_PROCESS_SCHEDULER_SETPARAM, p, t, KAUTH_ARG(lpolicy),
		    KAUTH_ARG(kpri));
		if (error) {
			lwp_unlock(t);
			break;
		}

		/* Set the scheduling class, change the priority */
		t->l_class = lpolicy;
		lwp_changepri(t, kpri);
		lwp_unlock(t);
	}
	mutex_exit(p->p_lock);
	return (lcnt == 0) ? ESRCH : error;
}

/*
 * Set scheduling parameters.
 */
int
sys__sched_setparam(struct lwp *l, const struct sys__sched_setparam_args *uap,
    register_t *retval)
{
	/* {
		syscallarg(pid_t) pid;
		syscallarg(lwpid_t) lid;
		syscallarg(int) policy;
		syscallarg(const struct sched_param *) params;
	} */
	struct sched_param params;
	int error;

	/* Get the parameters from the user-space */
	error = copyin(SCARG(uap, params), &params, sizeof(params));
	if (error)
		goto out;

	error = do_sched_setparam(SCARG(uap, pid), SCARG(uap, lid),
	    SCARG(uap, policy), &params);
out:
	return error;
}

/*
 * do_sched_getparam:
 *
 * if lid=0, returns the parameter of the first LWP in the process.
 */
int
do_sched_getparam(pid_t pid, lwpid_t lid, int *policy,
    struct sched_param *params)
{
	struct sched_param lparams;
	struct lwp *t;
	int error, lpolicy;

	if (pid < 0 || lid < 0)
		return EINVAL;

	t = lwp_find2(pid, lid); /* acquire p_lock */
	if (t == NULL)
		return ESRCH;

	/* Check the permission */
	error = kauth_authorize_process(kauth_cred_get(),
	    KAUTH_PROCESS_SCHEDULER_GETPARAM, t->l_proc, NULL, NULL, NULL);
	if (error != 0) {
		mutex_exit(t->l_proc->p_lock);
		return error;
	}

	lwp_lock(t);
	lparams.sched_priority = t->l_priority;
	lpolicy = t->l_class;
	lwp_unlock(t);
	mutex_exit(t->l_proc->p_lock);

	/*
	 * convert to the user-visible priority value.
	 * it's an inversion of convert_pri().
	 *
	 * the SCHED_OTHER case is a bit arbitrary given that
	 *	- we don't allow setting the priority.
	 *	- the priority is dynamic.
	 */
	switch (lpolicy) {
	case SCHED_OTHER:
		lparams.sched_priority -= PRI_USER;
		break;
	case SCHED_RR:
	case SCHED_FIFO:
		lparams.sched_priority -= PRI_USER_RT;
		break;
	}

	if (policy != NULL)
		*policy = lpolicy;

	if (params != NULL)
		*params = lparams;

	return error;
}

/*
 * Get scheduling parameters.
 */
int
sys__sched_getparam(struct lwp *l, const struct sys__sched_getparam_args *uap,
    register_t *retval)
{
	/* {
		syscallarg(pid_t) pid;
		syscallarg(lwpid_t) lid;
		syscallarg(int *) policy;
		syscallarg(struct sched_param *) params;
	} */
	struct sched_param params;
	int error, policy;

	error = do_sched_getparam(SCARG(uap, pid), SCARG(uap, lid), &policy,
	    &params);
	if (error)
		goto out;

	error = copyout(&params, SCARG(uap, params), sizeof(params));
	if (error == 0 && SCARG(uap, policy) != NULL)
		error = copyout(&policy, SCARG(uap, policy), sizeof(int));
out:
	return error;
}

/*
 * Allocate the CPU set, and get it from userspace.
 */
static int
genkcpuset(kcpuset_t **dset, const cpuset_t *sset, size_t size)
{
	kcpuset_t *kset;
	int error;

	kcpuset_create(&kset, true);
	error = kcpuset_copyin(sset, kset, size);
	if (error) {
		kcpuset_unuse(kset, NULL);
	} else {
		*dset = kset;
	}
	return error;
}

/*
 * Set affinity.
 */
int
sys__sched_setaffinity(struct lwp *l,
    const struct sys__sched_setaffinity_args *uap, register_t *retval)
{
	/* {
		syscallarg(pid_t) pid;
		syscallarg(lwpid_t) lid;
		syscallarg(size_t) size;
		syscallarg(const cpuset_t *) cpuset;
	} */
	kcpuset_t *kcset, *kcpulst = NULL;
	struct cpu_info *ici, *ci;
	struct proc *p;
	struct lwp *t;
	CPU_INFO_ITERATOR cii;
	bool alloff;
	lwpid_t lid;
	u_int lcnt;
	int error;

	error = genkcpuset(&kcset, SCARG(uap, cpuset), SCARG(uap, size));
	if (error)
		return error;

	/*
	 * Traverse _each_ CPU to:
	 *  - Check that CPUs in the mask have no assigned processor set.
	 *  - Check that at least one CPU from the mask is online.
	 *  - Find the first target CPU to migrate.
	 *
	 * To avoid the race with CPU online/offline calls and processor sets,
	 * cpu_lock will be locked for the entire operation.
	 */
	ci = NULL;
	alloff = false;
	mutex_enter(&cpu_lock);
	for (CPU_INFO_FOREACH(cii, ici)) {
		struct schedstate_percpu *ispc;

		if (!kcpuset_isset(kcset, cpu_index(ici))) {
			continue;
		}

		ispc = &ici->ci_schedstate;
		/* Check that CPU is not in the processor-set */
		if (ispc->spc_psid != PS_NONE) {
			error = EPERM;
			goto out;
		}
		/* Skip offline CPUs */
		if (ispc->spc_flags & SPCF_OFFLINE) {
			alloff = true;
			continue;
		}
		/* Target CPU to migrate */
		if (ci == NULL) {
			ci = ici;
		}
	}
	if (ci == NULL) {
		if (alloff) {
			/* All CPUs in the set are offline */
			error = EPERM;
			goto out;
		}
		/* Empty set */
		kcpuset_unuse(kcset, &kcpulst);
		kcset = NULL;
	}

	if (SCARG(uap, pid) != 0) {
		/* Find the process */
		mutex_enter(&proc_lock);
		p = proc_find(SCARG(uap, pid));
		if (p == NULL) {
			mutex_exit(&proc_lock);
			error = ESRCH;
			goto out;
		}
		mutex_enter(p->p_lock);
		mutex_exit(&proc_lock);
		/* Disallow modification of system processes. */
		if ((p->p_flag & PK_SYSTEM) != 0) {
			mutex_exit(p->p_lock);
			error = EPERM;
			goto out;
		}
	} else {
		/* Use the calling process */
		p = l->l_proc;
		mutex_enter(p->p_lock);
	}

	/*
	 * Check the permission.
	 */
	error = kauth_authorize_process(l->l_cred,
	    KAUTH_PROCESS_SCHEDULER_SETAFFINITY, p, NULL, NULL, NULL);
	if (error != 0) {
		mutex_exit(p->p_lock);
		goto out;
	}

	/* Iterate through LWP(s). */
	lcnt = 0;
	lid = SCARG(uap, lid);
	LIST_FOREACH(t, &p->p_lwps, l_sibling) {
		if (lid && lid != t->l_lid) {
			continue;
		}
		lwp_lock(t);
		/* No affinity for zombie LWPs. */
		if (t->l_stat == LSZOMB) {
			lwp_unlock(t);
			continue;
		}
		/* First, release existing affinity, if any. */
		if (t->l_affinity) {
			kcpuset_unuse(t->l_affinity, &kcpulst);
		}
		if (kcset) {
			/*
			 * Hold a reference on affinity mask, assign mask to
			 * LWP and migrate it to another CPU (unlocks LWP).
			 */
			kcpuset_use(kcset);
			t->l_affinity = kcset;
			lwp_migrate(t, ci);
		} else {
			/* Old affinity mask is released, just clear. */
			t->l_affinity = NULL;
			lwp_unlock(t);
		}
		lcnt++;
	}
	mutex_exit(p->p_lock);
	if (lcnt == 0) {
		error = ESRCH;
	}
out:
	mutex_exit(&cpu_lock);

	/*
	 * Drop the initial reference (LWPs, if any, have the ownership now),
	 * and destroy whatever is in the G/C list, if filled.
	 */
	if (kcset) {
		kcpuset_unuse(kcset, &kcpulst);
	}
	if (kcpulst) {
		kcpuset_destroy(kcpulst);
	}
	return error;
}

/*
 * Get affinity.
 */
int
sys__sched_getaffinity(struct lwp *l,
    const struct sys__sched_getaffinity_args *uap, register_t *retval)
{
	/* {
		syscallarg(pid_t) pid;
		syscallarg(lwpid_t) lid;
		syscallarg(size_t) size;
		syscallarg(cpuset_t *) cpuset;
	} */
	struct lwp *t;
	kcpuset_t *kcset;
	int error;

	if (SCARG(uap, pid) < 0 || SCARG(uap, lid) < 0)
		return EINVAL;

	error = genkcpuset(&kcset, SCARG(uap, cpuset), SCARG(uap, size));
	if (error)
		return error;

	/* Locks the LWP */
	t = lwp_find2(SCARG(uap, pid), SCARG(uap, lid));
	if (t == NULL) {
		error = ESRCH;
		goto out;
	}
	/* Check the permission */
	if (kauth_authorize_process(l->l_cred,
	    KAUTH_PROCESS_SCHEDULER_GETAFFINITY, t->l_proc, NULL, NULL, NULL)) {
		mutex_exit(t->l_proc->p_lock);
		error = EPERM;
		goto out;
	}
	lwp_lock(t);
	if (t->l_affinity) {
		kcpuset_copy(kcset, t->l_affinity);
	} else {
		kcpuset_zero(kcset);
	}
	lwp_unlock(t);
	mutex_exit(t->l_proc->p_lock);

	error = kcpuset_copyout(kcset, SCARG(uap, cpuset), SCARG(uap, size));
out:
	kcpuset_unuse(kcset, NULL);
	return error;
}

/*
 * Priority protection for PTHREAD_PRIO_PROTECT. This is a weak
 * analogue of priority inheritance: temp raise the priority
 * of the caller when accessing a protected resource.
 */
int
sys__sched_protect(struct lwp *l,
    const struct sys__sched_protect_args *uap, register_t *retval)
{
        /* {
                syscallarg(int) priority;
		syscallarg(int *) opriority;
        } */
	int error;
	pri_t pri;

	KASSERT(l->l_inheritedprio == -1);
	KASSERT(l->l_auxprio == -1 || l->l_auxprio == l->l_protectprio);

	pri = SCARG(uap, priority);
	error = 0;
	lwp_lock(l);
	if (pri == -1) {
		/* back out priority changes */
		switch(l->l_protectdepth) {
		case 0:
			error = EINVAL;
			break;
		case 1:
			l->l_protectdepth = 0;
			l->l_protectprio = -1;
			l->l_auxprio = -1;
			break;
		default:
			l->l_protectdepth--;
			break;
		}
	} else if (pri < 0) {
		/* Just retrieve the current value, for debugging */
		if (l->l_protectprio == -1)
			error = ENOENT;
		else
			*retval = l->l_protectprio - PRI_USER_RT;
	} else if (__predict_false(pri < SCHED_PRI_MIN ||
	    pri > SCHED_PRI_MAX || l->l_priority > pri + PRI_USER_RT)) {
		/* must fail if existing priority is higher */
		error = EPERM;
	} else {
		/* play along but make no changes if not a realtime LWP. */
		l->l_protectdepth++;
		pri += PRI_USER_RT;
		if (__predict_true(l->l_class != SCHED_OTHER &&
		    pri > l->l_protectprio)) {
			l->l_protectprio = pri;
			l->l_auxprio = pri;
		}
	}
	lwp_unlock(l);

	return error;
}

/*
 * Yield.
 */
int
sys_sched_yield(struct lwp *l, const void *v, register_t *retval)
{

	yield();
	return 0;
}

/*
 * Sysctl nodes and initialization.
 */
static void
sysctl_sched_setup(struct sysctllog **clog)
{
	const struct sysctlnode *node = NULL;

	sysctl_createv(clog, 0, NULL, NULL,
		CTLFLAG_PERMANENT|CTLFLAG_IMMEDIATE,
		CTLTYPE_INT, "posix_sched",
		SYSCTL_DESCR("Version of IEEE Std 1003.1 and its "
			     "Process Scheduling option to which the "
			     "system attempts to conform"),
		NULL, _POSIX_PRIORITY_SCHEDULING, NULL, 0,
		CTL_KERN, CTL_CREATE, CTL_EOL);
	sysctl_createv(clog, 0, NULL, &node,
		CTLFLAG_PERMANENT,
		CTLTYPE_NODE, "sched",
		SYSCTL_DESCR("Scheduler options"),
		NULL, 0, NULL, 0,
		CTL_KERN, CTL_CREATE, CTL_EOL);

	if (node == NULL)
		return;

	sysctl_createv(clog, 0, &node, NULL,
		CTLFLAG_PERMANENT | CTLFLAG_IMMEDIATE,
		CTLTYPE_INT, "pri_min",
		SYSCTL_DESCR("Minimal POSIX real-time priority"),
		NULL, SCHED_PRI_MIN, NULL, 0,
		CTL_CREATE, CTL_EOL);
	sysctl_createv(clog, 0, &node, NULL,
		CTLFLAG_PERMANENT | CTLFLAG_IMMEDIATE,
		CTLTYPE_INT, "pri_max",
		SYSCTL_DESCR("Maximal POSIX real-time priority"),
		NULL, SCHED_PRI_MAX, NULL, 0,
		CTL_CREATE, CTL_EOL);
}

static int
sched_listener_cb(kauth_cred_t cred, kauth_action_t action, void *cookie,
    void *arg0, void *arg1, void *arg2, void *arg3)
{
	struct proc *p;
	int result;

	result = KAUTH_RESULT_DEFER;
	p = arg0;

	switch (action) {
	case KAUTH_PROCESS_SCHEDULER_GETPARAM:
		if (kauth_cred_uidmatch(cred, p->p_cred))
			result = KAUTH_RESULT_ALLOW;
		break;

	case KAUTH_PROCESS_SCHEDULER_SETPARAM:
		if (kauth_cred_uidmatch(cred, p->p_cred)) {
			struct lwp *l;
			int policy;
			pri_t priority;

			l = arg1;
			policy = (int)(unsigned long)arg2;
			priority = (pri_t)(unsigned long)arg3;

			if ((policy == l->l_class ||
			    (policy != SCHED_FIFO && policy != SCHED_RR)) &&
			    priority <= l->l_priority)
				result = KAUTH_RESULT_ALLOW;
		}

		break;

	case KAUTH_PROCESS_SCHEDULER_GETAFFINITY:
		result = KAUTH_RESULT_ALLOW;
		break;

	case KAUTH_PROCESS_SCHEDULER_SETAFFINITY:
		/* Privileged; we let the secmodel handle this. */
		break;

	default:
		break;
	}

	return result;
}

void
sched_init(void)
{

	sysctl_sched_setup(&sched_sysctl_log);

	sched_listener = kauth_listen_scope(KAUTH_SCOPE_PROCESS,
	    sched_listener_cb, NULL);
}