xref: /openbsd/sys/kern/kern_resource.c (revision 4bdff4be) 
1 /*	$OpenBSD: kern_resource.c,v 1.80 2023/09/13 14:25:49 claudio Exp $	*/
2 /*	$NetBSD: kern_resource.c,v 1.38 1996/10/23 07:19:38 matthias Exp $	*/
3 
4 /*-
5  * Copyright (c) 1982, 1986, 1991, 1993
6  *	The Regents of the University of California.  All rights reserved.
7  * (c) UNIX System Laboratories, Inc.
8  * All or some portions of this file are derived from material licensed
9  * to the University of California by American Telephone and Telegraph
10  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
11  * the permission of UNIX System Laboratories, Inc.
12  *
13  * Redistribution and use in source and binary forms, with or without
14  * modification, are permitted provided that the following conditions
15  * are met:
16  * 1. Redistributions of source code must retain the above copyright
17  *    notice, this list of conditions and the following disclaimer.
18  * 2. Redistributions in binary form must reproduce the above copyright
19  *    notice, this list of conditions and the following disclaimer in the
20  *    documentation and/or other materials provided with the distribution.
21  * 3. Neither the name of the University nor the names of its contributors
22  *    may be used to endorse or promote products derived from this software
23  *    without specific prior written permission.
24  *
25  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
26  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
27  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
28  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
29  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
30  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
31  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
32  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
33  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
34  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35  * SUCH DAMAGE.
36  *
37  *	@(#)kern_resource.c	8.5 (Berkeley) 1/21/94
38  */
39 
40 #include <sys/param.h>
41 #include <sys/systm.h>
42 #include <sys/kernel.h>
43 #include <sys/file.h>
44 #include <sys/resourcevar.h>
45 #include <sys/pool.h>
46 #include <sys/proc.h>
47 #include <sys/ktrace.h>
48 #include <sys/sched.h>
49 #include <sys/signalvar.h>
50 
51 #include <sys/mount.h>
52 #include <sys/syscallargs.h>
53 
54 #include <uvm/uvm_extern.h>
55 #include <uvm/uvm.h>
56 
57 /* Resource usage check interval in msec */
58 #define RUCHECK_INTERVAL	1000
59 
60 /* SIGXCPU interval in seconds of process runtime */
61 #define SIGXCPU_INTERVAL	5
62 
63 struct plimit	*lim_copy(struct plimit *);
64 struct plimit	*lim_write_begin(void);
65 void		 lim_write_commit(struct plimit *);
66 
67 void	tuagg_sub(struct tusage *, struct proc *, const struct timespec *);
68 
69 /*
70  * Patchable maximum data and stack limits.
71  */
72 rlim_t maxdmap = MAXDSIZ;
73 rlim_t maxsmap = MAXSSIZ;
74 
75 /*
76  * Serializes resource limit updates.
77  * This lock has to be held together with ps_mtx when updating
78  * the process' ps_limit.
79  */
80 struct rwlock rlimit_lock = RWLOCK_INITIALIZER("rlimitlk");
81 
82 /*
83  * Resource controls and accounting.
84  */
85 
86 int
87 sys_getpriority(struct proc *curp, void *v, register_t *retval)
88 {
89 	struct sys_getpriority_args /* {
90 		syscallarg(int) which;
91 		syscallarg(id_t) who;
92 	} */ *uap = v;
93 	struct process *pr;
94 	int low = NZERO + PRIO_MAX + 1;
95 
96 	switch (SCARG(uap, which)) {
97 
98 	case PRIO_PROCESS:
99 		if (SCARG(uap, who) == 0)
100 			pr = curp->p_p;
101 		else
102 			pr = prfind(SCARG(uap, who));
103 		if (pr == NULL)
104 			break;
105 		if (pr->ps_nice < low)
106 			low = pr->ps_nice;
107 		break;
108 
109 	case PRIO_PGRP: {
110 		struct pgrp *pg;
111 
112 		if (SCARG(uap, who) == 0)
113 			pg = curp->p_p->ps_pgrp;
114 		else if ((pg = pgfind(SCARG(uap, who))) == NULL)
115 			break;
116 		LIST_FOREACH(pr, &pg->pg_members, ps_pglist)
117 			if (pr->ps_nice < low)
118 				low = pr->ps_nice;
119 		break;
120 	}
121 
122 	case PRIO_USER:
123 		if (SCARG(uap, who) == 0)
124 			SCARG(uap, who) = curp->p_ucred->cr_uid;
125 		LIST_FOREACH(pr, &allprocess, ps_list)
126 			if (pr->ps_ucred->cr_uid == SCARG(uap, who) &&
127 			    pr->ps_nice < low)
128 				low = pr->ps_nice;
129 		break;
130 
131 	default:
132 		return (EINVAL);
133 	}
134 	if (low == NZERO + PRIO_MAX + 1)
135 		return (ESRCH);
136 	*retval = low - NZERO;
137 	return (0);
138 }
139 
140 int
141 sys_setpriority(struct proc *curp, void *v, register_t *retval)
142 {
143 	struct sys_setpriority_args /* {
144 		syscallarg(int) which;
145 		syscallarg(id_t) who;
146 		syscallarg(int) prio;
147 	} */ *uap = v;
148 	struct process *pr;
149 	int found = 0, error = 0;
150 
151 	switch (SCARG(uap, which)) {
152 
153 	case PRIO_PROCESS:
154 		if (SCARG(uap, who) == 0)
155 			pr = curp->p_p;
156 		else
157 			pr = prfind(SCARG(uap, who));
158 		if (pr == NULL)
159 			break;
160 		error = donice(curp, pr, SCARG(uap, prio));
161 		found = 1;
162 		break;
163 
164 	case PRIO_PGRP: {
165 		struct pgrp *pg;
166 
167 		if (SCARG(uap, who) == 0)
168 			pg = curp->p_p->ps_pgrp;
169 		else if ((pg = pgfind(SCARG(uap, who))) == NULL)
170 			break;
171 		LIST_FOREACH(pr, &pg->pg_members, ps_pglist) {
172 			error = donice(curp, pr, SCARG(uap, prio));
173 			found = 1;
174 		}
175 		break;
176 	}
177 
178 	case PRIO_USER:
179 		if (SCARG(uap, who) == 0)
180 			SCARG(uap, who) = curp->p_ucred->cr_uid;
181 		LIST_FOREACH(pr, &allprocess, ps_list)
182 			if (pr->ps_ucred->cr_uid == SCARG(uap, who)) {
183 				error = donice(curp, pr, SCARG(uap, prio));
184 				found = 1;
185 			}
186 		break;
187 
188 	default:
189 		return (EINVAL);
190 	}
191 	if (!found)
192 		return (ESRCH);
193 	return (error);
194 }
195 
196 int
197 donice(struct proc *curp, struct process *chgpr, int n)
198 {
199 	struct ucred *ucred = curp->p_ucred;
200 	struct proc *p;
201 	int s;
202 
203 	if (ucred->cr_uid != 0 && ucred->cr_ruid != 0 &&
204 	    ucred->cr_uid != chgpr->ps_ucred->cr_uid &&
205 	    ucred->cr_ruid != chgpr->ps_ucred->cr_uid)
206 		return (EPERM);
207 	if (n > PRIO_MAX)
208 		n = PRIO_MAX;
209 	if (n < PRIO_MIN)
210 		n = PRIO_MIN;
211 	n += NZERO;
212 	if (n < chgpr->ps_nice && suser(curp))
213 		return (EACCES);
214 	chgpr->ps_nice = n;
215 	SCHED_LOCK(s);
216 	TAILQ_FOREACH(p, &chgpr->ps_threads, p_thr_link) {
217 		setpriority(p, p->p_estcpu, n);
218 	}
219 	SCHED_UNLOCK(s);
220 	return (0);
221 }
222 
223 int
224 sys_setrlimit(struct proc *p, void *v, register_t *retval)
225 {
226 	struct sys_setrlimit_args /* {
227 		syscallarg(int) which;
228 		syscallarg(const struct rlimit *) rlp;
229 	} */ *uap = v;
230 	struct rlimit alim;
231 	int error;
232 
233 	error = copyin((caddr_t)SCARG(uap, rlp), (caddr_t)&alim,
234 		       sizeof (struct rlimit));
235 	if (error)
236 		return (error);
237 #ifdef KTRACE
238 	if (KTRPOINT(p, KTR_STRUCT))
239 		ktrrlimit(p, &alim);
240 #endif
241 	return (dosetrlimit(p, SCARG(uap, which), &alim));
242 }
243 
244 int
245 dosetrlimit(struct proc *p, u_int which, struct rlimit *limp)
246 {
247 	struct rlimit *alimp;
248 	struct plimit *limit;
249 	rlim_t maxlim;
250 	int error;
251 
252 	if (which >= RLIM_NLIMITS || limp->rlim_cur > limp->rlim_max)
253 		return (EINVAL);
254 
255 	rw_enter_write(&rlimit_lock);
256 
257 	alimp = &p->p_p->ps_limit->pl_rlimit[which];
258 	if (limp->rlim_max > alimp->rlim_max) {
259 		if ((error = suser(p)) != 0) {
260 			rw_exit_write(&rlimit_lock);
261 			return (error);
262 		}
263 	}
264 
265 	/* Get exclusive write access to the limit structure. */
266 	limit = lim_write_begin();
267 	alimp = &limit->pl_rlimit[which];
268 
269 	switch (which) {
270 	case RLIMIT_DATA:
271 		maxlim = maxdmap;
272 		break;
273 	case RLIMIT_STACK:
274 		maxlim = maxsmap;
275 		break;
276 	case RLIMIT_NOFILE:
277 		maxlim = maxfiles;
278 		break;
279 	case RLIMIT_NPROC:
280 		maxlim = maxprocess;
281 		break;
282 	default:
283 		maxlim = RLIM_INFINITY;
284 		break;
285 	}
286 
287 	if (limp->rlim_max > maxlim)
288 		limp->rlim_max = maxlim;
289 	if (limp->rlim_cur > limp->rlim_max)
290 		limp->rlim_cur = limp->rlim_max;
291 
292 	if (which == RLIMIT_CPU && limp->rlim_cur != RLIM_INFINITY &&
293 	    alimp->rlim_cur == RLIM_INFINITY)
294 		timeout_add_msec(&p->p_p->ps_rucheck_to, RUCHECK_INTERVAL);
295 
296 	if (which == RLIMIT_STACK) {
297 		/*
298 		 * Stack is allocated to the max at exec time with only
299 		 * "rlim_cur" bytes accessible.  If stack limit is going
300 		 * up make more accessible, if going down make inaccessible.
301 		 */
302 		if (limp->rlim_cur != alimp->rlim_cur) {
303 			vaddr_t addr;
304 			vsize_t size;
305 			vm_prot_t prot;
306 			struct vmspace *vm = p->p_vmspace;
307 
308 			if (limp->rlim_cur > alimp->rlim_cur) {
309 				prot = PROT_READ | PROT_WRITE;
310 				size = limp->rlim_cur - alimp->rlim_cur;
311 #ifdef MACHINE_STACK_GROWS_UP
312 				addr = (vaddr_t)vm->vm_maxsaddr +
313 				    alimp->rlim_cur;
314 #else
315 				addr = (vaddr_t)vm->vm_minsaddr -
316 				    limp->rlim_cur;
317 #endif
318 			} else {
319 				prot = PROT_NONE;
320 				size = alimp->rlim_cur - limp->rlim_cur;
321 #ifdef MACHINE_STACK_GROWS_UP
322 				addr = (vaddr_t)vm->vm_maxsaddr +
323 				    limp->rlim_cur;
324 #else
325 				addr = (vaddr_t)vm->vm_minsaddr -
326 				    alimp->rlim_cur;
327 #endif
328 			}
329 			addr = trunc_page(addr);
330 			size = round_page(size);
331 			KERNEL_LOCK();
332 			(void) uvm_map_protect(&vm->vm_map, addr,
333 			    addr+size, prot, UVM_ET_STACK, FALSE, FALSE);
334 			KERNEL_UNLOCK();
335 		}
336 	}
337 
338 	*alimp = *limp;
339 
340 	lim_write_commit(limit);
341 	rw_exit_write(&rlimit_lock);
342 
343 	return (0);
344 }
345 
346 int
347 sys_getrlimit(struct proc *p, void *v, register_t *retval)
348 {
349 	struct sys_getrlimit_args /* {
350 		syscallarg(int) which;
351 		syscallarg(struct rlimit *) rlp;
352 	} */ *uap = v;
353 	struct plimit *limit;
354 	struct rlimit alimp;
355 	int error;
356 
357 	if (SCARG(uap, which) < 0 || SCARG(uap, which) >= RLIM_NLIMITS)
358 		return (EINVAL);
359 	limit = lim_read_enter();
360 	alimp = limit->pl_rlimit[SCARG(uap, which)];
361 	lim_read_leave(limit);
362 	error = copyout(&alimp, SCARG(uap, rlp), sizeof(struct rlimit));
363 #ifdef KTRACE
364 	if (error == 0 && KTRPOINT(p, KTR_STRUCT))
365 		ktrrlimit(p, &alimp);
366 #endif
367 	return (error);
368 }
369 
370 void
371 tuagg_sub(struct tusage *tup, struct proc *p, const struct timespec *ts)
372 {
373 	if (ts != NULL)
374 		timespecadd(&tup->tu_runtime, ts, &tup->tu_runtime);
375 	tup->tu_uticks += p->p_uticks;
376 	tup->tu_sticks += p->p_sticks;
377 	tup->tu_iticks += p->p_iticks;
378 }
379 
380 /*
381  * Aggregate a single thread's immediate time counts into the running
382  * totals for the thread and process
383  */
384 void
385 tuagg_locked(struct process *pr, struct proc *p, const struct timespec *ts)
386 {
387 	tuagg_sub(&pr->ps_tu, p, ts);
388 	tuagg_sub(&p->p_tu, p, ts);
389 	p->p_uticks = 0;
390 	p->p_sticks = 0;
391 	p->p_iticks = 0;
392 }
393 
394 void
395 tuagg(struct process *pr, struct proc *p)
396 {
397 	int s;
398 
399 	SCHED_LOCK(s);
400 	tuagg_locked(pr, p, NULL);
401 	SCHED_UNLOCK(s);
402 }
403 
404 /*
405  * Transform the running time and tick information in a struct tusage
406  * into user, system, and interrupt time usage.
407  */
408 void
409 calctsru(struct tusage *tup, struct timespec *up, struct timespec *sp,
410     struct timespec *ip)
411 {
412 	u_quad_t st, ut, it;
413 
414 	st = tup->tu_sticks;
415 	ut = tup->tu_uticks;
416 	it = tup->tu_iticks;
417 
418 	if (st + ut + it == 0) {
419 		timespecclear(up);
420 		timespecclear(sp);
421 		if (ip != NULL)
422 			timespecclear(ip);
423 		return;
424 	}
425 
426 	st = st * 1000000000 / stathz;
427 	sp->tv_sec = st / 1000000000;
428 	sp->tv_nsec = st % 1000000000;
429 	ut = ut * 1000000000 / stathz;
430 	up->tv_sec = ut / 1000000000;
431 	up->tv_nsec = ut % 1000000000;
432 	if (ip != NULL) {
433 		it = it * 1000000000 / stathz;
434 		ip->tv_sec = it / 1000000000;
435 		ip->tv_nsec = it % 1000000000;
436 	}
437 }
438 
439 void
440 calcru(struct tusage *tup, struct timeval *up, struct timeval *sp,
441     struct timeval *ip)
442 {
443 	struct timespec u, s, i;
444 
445 	calctsru(tup, &u, &s, ip != NULL ? &i : NULL);
446 	TIMESPEC_TO_TIMEVAL(up, &u);
447 	TIMESPEC_TO_TIMEVAL(sp, &s);
448 	if (ip != NULL)
449 		TIMESPEC_TO_TIMEVAL(ip, &i);
450 }
451 
452 int
453 sys_getrusage(struct proc *p, void *v, register_t *retval)
454 {
455 	struct sys_getrusage_args /* {
456 		syscallarg(int) who;
457 		syscallarg(struct rusage *) rusage;
458 	} */ *uap = v;
459 	struct rusage ru;
460 	int error;
461 
462 	error = dogetrusage(p, SCARG(uap, who), &ru);
463 	if (error == 0) {
464 		error = copyout(&ru, SCARG(uap, rusage), sizeof(ru));
465 #ifdef KTRACE
466 		if (error == 0 && KTRPOINT(p, KTR_STRUCT))
467 			ktrrusage(p, &ru);
468 #endif
469 	}
470 	return (error);
471 }
472 
473 int
474 dogetrusage(struct proc *p, int who, struct rusage *rup)
475 {
476 	struct process *pr = p->p_p;
477 	struct proc *q;
478 
479 	switch (who) {
480 
481 	case RUSAGE_SELF:
482 		/* start with the sum of dead threads, if any */
483 		if (pr->ps_ru != NULL)
484 			*rup = *pr->ps_ru;
485 		else
486 			memset(rup, 0, sizeof(*rup));
487 
488 		/* add on all living threads */
489 		TAILQ_FOREACH(q, &pr->ps_threads, p_thr_link) {
490 			ruadd(rup, &q->p_ru);
491 			tuagg(pr, q);
492 		}
493 
494 		calcru(&pr->ps_tu, &rup->ru_utime, &rup->ru_stime, NULL);
495 		break;
496 
497 	case RUSAGE_THREAD:
498 		*rup = p->p_ru;
499 		calcru(&p->p_tu, &rup->ru_utime, &rup->ru_stime, NULL);
500 		break;
501 
502 	case RUSAGE_CHILDREN:
503 		*rup = pr->ps_cru;
504 		break;
505 
506 	default:
507 		return (EINVAL);
508 	}
509 	return (0);
510 }
511 
512 void
513 ruadd(struct rusage *ru, struct rusage *ru2)
514 {
515 	long *ip, *ip2;
516 	int i;
517 
518 	timeradd(&ru->ru_utime, &ru2->ru_utime, &ru->ru_utime);
519 	timeradd(&ru->ru_stime, &ru2->ru_stime, &ru->ru_stime);
520 	if (ru->ru_maxrss < ru2->ru_maxrss)
521 		ru->ru_maxrss = ru2->ru_maxrss;
522 	ip = &ru->ru_first; ip2 = &ru2->ru_first;
523 	for (i = &ru->ru_last - &ru->ru_first; i >= 0; i--)
524 		*ip++ += *ip2++;
525 }
526 
527 /*
528  * Check if the process exceeds its cpu resource allocation.
529  * If over max, kill it.
530  */
531 void
532 rucheck(void *arg)
533 {
534 	struct rlimit rlim;
535 	struct process *pr = arg;
536 	time_t runtime;
537 	int s;
538 
539 	KERNEL_ASSERT_LOCKED();
540 
541 	SCHED_LOCK(s);
542 	runtime = pr->ps_tu.tu_runtime.tv_sec;
543 	SCHED_UNLOCK(s);
544 
545 	mtx_enter(&pr->ps_mtx);
546 	rlim = pr->ps_limit->pl_rlimit[RLIMIT_CPU];
547 	mtx_leave(&pr->ps_mtx);
548 
549 	if ((rlim_t)runtime >= rlim.rlim_cur) {
550 		if ((rlim_t)runtime >= rlim.rlim_max) {
551 			prsignal(pr, SIGKILL);
552 		} else if (runtime >= pr->ps_nextxcpu) {
553 			prsignal(pr, SIGXCPU);
554 			pr->ps_nextxcpu = runtime + SIGXCPU_INTERVAL;
555 		}
556 	}
557 
558 	timeout_add_msec(&pr->ps_rucheck_to, RUCHECK_INTERVAL);
559 }
560 
561 struct pool plimit_pool;
562 
563 void
564 lim_startup(struct plimit *limit0)
565 {
566 	rlim_t lim;
567 	int i;
568 
569 	pool_init(&plimit_pool, sizeof(struct plimit), 0, IPL_MPFLOOR,
570 	    PR_WAITOK, "plimitpl", NULL);
571 
572 	for (i = 0; i < nitems(limit0->pl_rlimit); i++)
573 		limit0->pl_rlimit[i].rlim_cur =
574 		    limit0->pl_rlimit[i].rlim_max = RLIM_INFINITY;
575 	limit0->pl_rlimit[RLIMIT_NOFILE].rlim_cur = NOFILE;
576 	limit0->pl_rlimit[RLIMIT_NOFILE].rlim_max = MIN(NOFILE_MAX,
577 	    (maxfiles - NOFILE > NOFILE) ? maxfiles - NOFILE : NOFILE);
578 	limit0->pl_rlimit[RLIMIT_NPROC].rlim_cur = MAXUPRC;
579 	lim = ptoa(uvmexp.free);
580 	limit0->pl_rlimit[RLIMIT_RSS].rlim_max = lim;
581 	lim = ptoa(64*1024);		/* Default to very low */
582 	limit0->pl_rlimit[RLIMIT_MEMLOCK].rlim_max = lim;
583 	limit0->pl_rlimit[RLIMIT_MEMLOCK].rlim_cur = lim / 3;
584 	refcnt_init(&limit0->pl_refcnt);
585 }
586 
587 /*
588  * Make a copy of the plimit structure.
589  * We share these structures copy-on-write after fork,
590  * and copy when a limit is changed.
591  */
592 struct plimit *
593 lim_copy(struct plimit *lim)
594 {
595 	struct plimit *newlim;
596 
597 	newlim = pool_get(&plimit_pool, PR_WAITOK);
598 	memcpy(newlim->pl_rlimit, lim->pl_rlimit,
599 	    sizeof(struct rlimit) * RLIM_NLIMITS);
600 	refcnt_init(&newlim->pl_refcnt);
601 	return (newlim);
602 }
603 
604 void
605 lim_free(struct plimit *lim)
606 {
607 	if (refcnt_rele(&lim->pl_refcnt) == 0)
608 		return;
609 	pool_put(&plimit_pool, lim);
610 }
611 
612 void
613 lim_fork(struct process *parent, struct process *child)
614 {
615 	struct plimit *limit;
616 
617 	mtx_enter(&parent->ps_mtx);
618 	limit = parent->ps_limit;
619 	refcnt_take(&limit->pl_refcnt);
620 	mtx_leave(&parent->ps_mtx);
621 
622 	child->ps_limit = limit;
623 
624 	if (limit->pl_rlimit[RLIMIT_CPU].rlim_cur != RLIM_INFINITY)
625 		timeout_add_msec(&child->ps_rucheck_to, RUCHECK_INTERVAL);
626 }
627 
628 /*
629  * Return an exclusive write reference to the process' resource limit structure.
630  * The caller has to release the structure by calling lim_write_commit().
631  *
632  * This invalidates any plimit read reference held by the calling thread.
633  */
634 struct plimit *
635 lim_write_begin(void)
636 {
637 	struct plimit *limit;
638 	struct proc *p = curproc;
639 
640 	rw_assert_wrlock(&rlimit_lock);
641 
642 	if (p->p_limit != NULL)
643 		lim_free(p->p_limit);
644 	p->p_limit = NULL;
645 
646 	/*
647 	 * It is safe to access ps_limit here without holding ps_mtx
648 	 * because rlimit_lock excludes other writers.
649 	 */
650 
651 	limit = p->p_p->ps_limit;
652 	if (P_HASSIBLING(p) || refcnt_shared(&limit->pl_refcnt))
653 		limit = lim_copy(limit);
654 
655 	return (limit);
656 }
657 
658 /*
659  * Finish exclusive write access to the plimit structure.
660  * This makes the structure visible to other threads in the process.
661  */
662 void
663 lim_write_commit(struct plimit *limit)
664 {
665 	struct plimit *olimit;
666 	struct proc *p = curproc;
667 
668 	rw_assert_wrlock(&rlimit_lock);
669 
670 	if (limit != p->p_p->ps_limit) {
671 		mtx_enter(&p->p_p->ps_mtx);
672 		olimit = p->p_p->ps_limit;
673 		p->p_p->ps_limit = limit;
674 		mtx_leave(&p->p_p->ps_mtx);
675 
676 		lim_free(olimit);
677 	}
678 }
679 
680 /*
681  * Begin read access to the process' resource limit structure.
682  * The access has to be finished by calling lim_read_leave().
683  *
684  * Sections denoted by lim_read_enter() and lim_read_leave() cannot nest.
685  */
686 struct plimit *
687 lim_read_enter(void)
688 {
689 	struct plimit *limit;
690 	struct proc *p = curproc;
691 	struct process *pr = p->p_p;
692 
693 	/*
694 	 * This thread might not observe the latest value of ps_limit
695 	 * if another thread updated the limits very recently on another CPU.
696 	 * However, the anomaly should disappear quickly, especially if
697 	 * there is any synchronization activity between the threads (or
698 	 * the CPUs).
699 	 */
700 
701 	limit = p->p_limit;
702 	if (limit != pr->ps_limit) {
703 		mtx_enter(&pr->ps_mtx);
704 		limit = pr->ps_limit;
705 		refcnt_take(&limit->pl_refcnt);
706 		mtx_leave(&pr->ps_mtx);
707 		if (p->p_limit != NULL)
708 			lim_free(p->p_limit);
709 		p->p_limit = limit;
710 	}
711 	KASSERT(limit != NULL);
712 	return (limit);
713 }
714 
715 /*
716  * Get the value of the resource limit in given process.
717  */
718 rlim_t
719 lim_cur_proc(struct proc *p, int which)
720 {
721 	struct process *pr = p->p_p;
722 	rlim_t val;
723 
724 	KASSERT(which >= 0 && which < RLIM_NLIMITS);
725 
726 	mtx_enter(&pr->ps_mtx);
727 	val = pr->ps_limit->pl_rlimit[which].rlim_cur;
728 	mtx_leave(&pr->ps_mtx);
729 	return (val);
730 }
731