FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_fork.c
1 /*
2 * Copyright (c) 1982, 1986, 1989, 1991, 1993
3 * The Regents of the University of California. All rights reserved.
4 * (c) UNIX System Laboratories, Inc.
5 * All or some portions of this file are derived from material licensed
6 * to the University of California by American Telephone and Telegraph
7 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
8 * the permission of UNIX System Laboratories, Inc.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 * 3. Neither the name of the University nor the names of its contributors
19 * may be used to endorse or promote products derived from this software
20 * without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 *
34 * @(#)kern_fork.c 8.6 (Berkeley) 4/8/94
35 * $FreeBSD: src/sys/kern/kern_fork.c,v 1.72.2.14 2003/06/26 04:15:10 silby Exp $
36 */
37
38 #include "opt_ktrace.h"
39
40 #include <sys/param.h>
41 #include <sys/systm.h>
42 #include <sys/sysproto.h>
43 #include <sys/filedesc.h>
44 #include <sys/kernel.h>
45 #include <sys/sysctl.h>
46 #include <sys/malloc.h>
47 #include <sys/proc.h>
48 #include <sys/resourcevar.h>
49 #include <sys/vnode.h>
50 #include <sys/acct.h>
51 #include <sys/ktrace.h>
52 #include <sys/unistd.h>
53 #include <sys/jail.h>
54
55 #include <vm/vm.h>
56 #include <sys/lock.h>
57 #include <vm/pmap.h>
58 #include <vm/vm_map.h>
59 #include <vm/vm_extern.h>
60
61 #include <sys/vmmeter.h>
62 #include <sys/refcount.h>
63 #include <sys/thread2.h>
64 #include <sys/signal2.h>
65 #include <sys/spinlock2.h>
66
67 #include <sys/dsched.h>
68
69 static MALLOC_DEFINE(M_ATFORK, "atfork", "atfork callback");
70
71 /*
72 * These are the stuctures used to create a callout list for things to do
73 * when forking a process
74 */
75 struct forklist {
76 forklist_fn function;
77 TAILQ_ENTRY(forklist) next;
78 };
79
80 TAILQ_HEAD(forklist_head, forklist);
81 static struct forklist_head fork_list = TAILQ_HEAD_INITIALIZER(fork_list);
82
83 static struct lwp *lwp_fork(struct lwp *, struct proc *, int flags);
84
85 int forksleep; /* Place for fork1() to sleep on. */
86
87 /*
88 * Red-Black tree support for LWPs
89 */
90
91 static int
92 rb_lwp_compare(struct lwp *lp1, struct lwp *lp2)
93 {
94 if (lp1->lwp_tid < lp2->lwp_tid)
95 return(-1);
96 if (lp1->lwp_tid > lp2->lwp_tid)
97 return(1);
98 return(0);
99 }
100
101 RB_GENERATE2(lwp_rb_tree, lwp, u.lwp_rbnode, rb_lwp_compare, lwpid_t, lwp_tid);
102
103 /*
104 * fork() system call
105 */
106 int
107 sys_fork(struct fork_args *uap)
108 {
109 struct lwp *lp = curthread->td_lwp;
110 struct proc *p2;
111 int error;
112
113 error = fork1(lp, RFFDG | RFPROC | RFPGLOCK, &p2);
114 if (error == 0) {
115 PHOLD(p2);
116 start_forked_proc(lp, p2);
117 uap->sysmsg_fds[0] = p2->p_pid;
118 uap->sysmsg_fds[1] = 0;
119 PRELE(p2);
120 }
121 return error;
122 }
123
124 /*
125 * vfork() system call
126 */
127 int
128 sys_vfork(struct vfork_args *uap)
129 {
130 struct lwp *lp = curthread->td_lwp;
131 struct proc *p2;
132 int error;
133
134 error = fork1(lp, RFFDG | RFPROC | RFPPWAIT | RFMEM | RFPGLOCK, &p2);
135 if (error == 0) {
136 PHOLD(p2);
137 start_forked_proc(lp, p2);
138 uap->sysmsg_fds[0] = p2->p_pid;
139 uap->sysmsg_fds[1] = 0;
140 PRELE(p2);
141 }
142 return error;
143 }
144
145 /*
146 * Handle rforks. An rfork may (1) operate on the current process without
147 * creating a new, (2) create a new process that shared the current process's
148 * vmspace, signals, and/or descriptors, or (3) create a new process that does
149 * not share these things (normal fork).
150 *
151 * Note that we only call start_forked_proc() if a new process is actually
152 * created.
153 *
154 * rfork { int flags }
155 */
156 int
157 sys_rfork(struct rfork_args *uap)
158 {
159 struct lwp *lp = curthread->td_lwp;
160 struct proc *p2;
161 int error;
162
163 if ((uap->flags & RFKERNELONLY) != 0)
164 return (EINVAL);
165
166 error = fork1(lp, uap->flags | RFPGLOCK, &p2);
167 if (error == 0) {
168 if (p2) {
169 PHOLD(p2);
170 start_forked_proc(lp, p2);
171 uap->sysmsg_fds[0] = p2->p_pid;
172 uap->sysmsg_fds[1] = 0;
173 PRELE(p2);
174 } else {
175 uap->sysmsg_fds[0] = 0;
176 uap->sysmsg_fds[1] = 0;
177 }
178 }
179 return error;
180 }
181
182 /*
183 * Low level thread create used by pthreads.
184 */
185 int
186 sys_lwp_create(struct lwp_create_args *uap)
187 {
188 struct proc *p = curproc;
189 struct lwp *lp;
190 struct lwp_params params;
191 int error;
192
193 error = copyin(uap->params, ¶ms, sizeof(params));
194 if (error)
195 goto fail2;
196
197 lwkt_gettoken(&p->p_token);
198 plimit_lwp_fork(p); /* force exclusive access */
199 lp = lwp_fork(curthread->td_lwp, p, RFPROC);
200 error = cpu_prepare_lwp(lp, ¶ms);
201 if (error)
202 goto fail;
203 if (params.tid1 != NULL &&
204 (error = copyout(&lp->lwp_tid, params.tid1, sizeof(lp->lwp_tid))))
205 goto fail;
206 if (params.tid2 != NULL &&
207 (error = copyout(&lp->lwp_tid, params.tid2, sizeof(lp->lwp_tid))))
208 goto fail;
209
210 /*
211 * Now schedule the new lwp.
212 */
213 p->p_usched->resetpriority(lp);
214 crit_enter();
215 lp->lwp_stat = LSRUN;
216 p->p_usched->setrunqueue(lp);
217 crit_exit();
218 lwkt_reltoken(&p->p_token);
219
220 return (0);
221
222 fail:
223 lwp_rb_tree_RB_REMOVE(&p->p_lwp_tree, lp);
224 --p->p_nthreads;
225 /* lwp_dispose expects an exited lwp, and a held proc */
226 atomic_set_int(&lp->lwp_mpflags, LWP_MP_WEXIT);
227 lp->lwp_thread->td_flags |= TDF_EXITING;
228 lwkt_remove_tdallq(lp->lwp_thread);
229 PHOLD(p);
230 biosched_done(lp->lwp_thread);
231 dsched_exit_thread(lp->lwp_thread);
232 lwp_dispose(lp);
233 lwkt_reltoken(&p->p_token);
234 fail2:
235 return (error);
236 }
237
238 int nprocs = 1; /* process 0 */
239
240 int
241 fork1(struct lwp *lp1, int flags, struct proc **procp)
242 {
243 struct proc *p1 = lp1->lwp_proc;
244 struct proc *p2;
245 struct proc *pptr;
246 struct pgrp *p1grp;
247 struct pgrp *plkgrp;
248 uid_t uid;
249 int ok, error;
250 static int curfail = 0;
251 static struct timeval lastfail;
252 struct forklist *ep;
253 struct filedesc_to_leader *fdtol;
254
255 if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
256 return (EINVAL);
257
258 lwkt_gettoken(&p1->p_token);
259 plkgrp = NULL;
260 p2 = NULL;
261
262 /*
263 * Here we don't create a new process, but we divorce
264 * certain parts of a process from itself.
265 */
266 if ((flags & RFPROC) == 0) {
267 /*
268 * This kind of stunt does not work anymore if
269 * there are native threads (lwps) running
270 */
271 if (p1->p_nthreads != 1) {
272 error = EINVAL;
273 goto done;
274 }
275
276 vm_fork(p1, 0, flags);
277
278 /*
279 * Close all file descriptors.
280 */
281 if (flags & RFCFDG) {
282 struct filedesc *fdtmp;
283 fdtmp = fdinit(p1);
284 fdfree(p1, fdtmp);
285 }
286
287 /*
288 * Unshare file descriptors (from parent.)
289 */
290 if (flags & RFFDG) {
291 if (p1->p_fd->fd_refcnt > 1) {
292 struct filedesc *newfd;
293 error = fdcopy(p1, &newfd);
294 if (error != 0) {
295 error = ENOMEM;
296 goto done;
297 }
298 fdfree(p1, newfd);
299 }
300 }
301 *procp = NULL;
302 error = 0;
303 goto done;
304 }
305
306 /*
307 * Interlock against process group signal delivery. If signals
308 * are pending after the interlock is obtained we have to restart
309 * the system call to process the signals. If we don't the child
310 * can miss a pgsignal (such as ^C) sent during the fork.
311 *
312 * We can't use CURSIG() here because it will process any STOPs
313 * and cause the process group lock to be held indefinitely. If
314 * a STOP occurs, the fork will be restarted after the CONT.
315 */
316 p1grp = p1->p_pgrp;
317 if ((flags & RFPGLOCK) && (plkgrp = p1->p_pgrp) != NULL) {
318 pgref(plkgrp);
319 lockmgr(&plkgrp->pg_lock, LK_SHARED);
320 if (CURSIG_NOBLOCK(lp1)) {
321 error = ERESTART;
322 goto done;
323 }
324 }
325
326 /*
327 * Although process entries are dynamically created, we still keep
328 * a global limit on the maximum number we will create. Don't allow
329 * a nonprivileged user to use the last ten processes; don't let root
330 * exceed the limit. The variable nprocs is the current number of
331 * processes, maxproc is the limit.
332 */
333 uid = lp1->lwp_thread->td_ucred->cr_ruid;
334 if ((nprocs >= maxproc - 10 && uid != 0) || nprocs >= maxproc) {
335 if (ppsratecheck(&lastfail, &curfail, 1))
336 kprintf("maxproc limit exceeded by uid %d, please "
337 "see tuning(7) and login.conf(5).\n", uid);
338 tsleep(&forksleep, 0, "fork", hz / 2);
339 error = EAGAIN;
340 goto done;
341 }
342
343 /*
344 * Increment the nprocs resource before blocking can occur. There
345 * are hard-limits as to the number of processes that can run.
346 */
347 atomic_add_int(&nprocs, 1);
348
349 /*
350 * Increment the count of procs running with this uid. Don't allow
351 * a nonprivileged user to exceed their current limit.
352 */
353 ok = chgproccnt(lp1->lwp_thread->td_ucred->cr_ruidinfo, 1,
354 (uid != 0) ? p1->p_rlimit[RLIMIT_NPROC].rlim_cur : 0);
355 if (!ok) {
356 /*
357 * Back out the process count
358 */
359 atomic_add_int(&nprocs, -1);
360 if (ppsratecheck(&lastfail, &curfail, 1))
361 kprintf("maxproc limit exceeded by uid %d, please "
362 "see tuning(7) and login.conf(5).\n", uid);
363 tsleep(&forksleep, 0, "fork", hz / 2);
364 error = EAGAIN;
365 goto done;
366 }
367
368 /*
369 * Allocate a new process, don't get fancy: zero the structure.
370 */
371 p2 = kmalloc(sizeof(struct proc), M_PROC, M_WAITOK|M_ZERO);
372
373 /*
374 * Core initialization. SIDL is a safety state that protects the
375 * partially initialized process once it starts getting hooked
376 * into system structures and becomes addressable.
377 *
378 * We must be sure to acquire p2->p_token as well, we must hold it
379 * once the process is on the allproc list to avoid things such
380 * as competing modifications to p_flags.
381 */
382 p2->p_lasttid = -1; /* first tid will be 0 */
383 p2->p_stat = SIDL;
384
385 RB_INIT(&p2->p_lwp_tree);
386 spin_init(&p2->p_spin);
387 lwkt_token_init(&p2->p_token, "proc");
388 lwkt_gettoken(&p2->p_token);
389
390 /*
391 * Setup linkage for kernel based threading XXX lwp. Also add the
392 * process to the allproclist.
393 *
394 * The process structure is addressable after this point.
395 */
396 if (flags & RFTHREAD) {
397 p2->p_peers = p1->p_peers;
398 p1->p_peers = p2;
399 p2->p_leader = p1->p_leader;
400 } else {
401 p2->p_leader = p2;
402 }
403 proc_add_allproc(p2);
404
405 /*
406 * Initialize the section which is copied verbatim from the parent.
407 */
408 bcopy(&p1->p_startcopy, &p2->p_startcopy,
409 ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy));
410
411 /*
412 * Duplicate sub-structures as needed. Increase reference counts
413 * on shared objects.
414 *
415 * NOTE: because we are now on the allproc list it is possible for
416 * other consumers to gain temporary references to p2
417 * (p2->p_lock can change).
418 */
419 if (p1->p_flags & P_PROFIL)
420 startprofclock(p2);
421 p2->p_ucred = crhold(lp1->lwp_thread->td_ucred);
422
423 if (jailed(p2->p_ucred))
424 p2->p_flags |= P_JAILED;
425
426 if (p2->p_args)
427 refcount_acquire(&p2->p_args->ar_ref);
428
429 p2->p_usched = p1->p_usched;
430 /* XXX: verify copy of the secondary iosched stuff */
431 dsched_new_proc(p2);
432
433 if (flags & RFSIGSHARE) {
434 p2->p_sigacts = p1->p_sigacts;
435 refcount_acquire(&p2->p_sigacts->ps_refcnt);
436 } else {
437 p2->p_sigacts = kmalloc(sizeof(*p2->p_sigacts),
438 M_SUBPROC, M_WAITOK);
439 bcopy(p1->p_sigacts, p2->p_sigacts, sizeof(*p2->p_sigacts));
440 refcount_init(&p2->p_sigacts->ps_refcnt, 1);
441 }
442 if (flags & RFLINUXTHPN)
443 p2->p_sigparent = SIGUSR1;
444 else
445 p2->p_sigparent = SIGCHLD;
446
447 /* bump references to the text vnode (for procfs) */
448 p2->p_textvp = p1->p_textvp;
449 if (p2->p_textvp)
450 vref(p2->p_textvp);
451
452 /* copy namecache handle to the text file */
453 if (p1->p_textnch.mount)
454 cache_copy(&p1->p_textnch, &p2->p_textnch);
455
456 /*
457 * Handle file descriptors
458 */
459 if (flags & RFCFDG) {
460 p2->p_fd = fdinit(p1);
461 fdtol = NULL;
462 } else if (flags & RFFDG) {
463 error = fdcopy(p1, &p2->p_fd);
464 if (error != 0) {
465 error = ENOMEM;
466 goto done;
467 }
468 fdtol = NULL;
469 } else {
470 p2->p_fd = fdshare(p1);
471 if (p1->p_fdtol == NULL) {
472 p1->p_fdtol = filedesc_to_leader_alloc(NULL,
473 p1->p_leader);
474 }
475 if ((flags & RFTHREAD) != 0) {
476 /*
477 * Shared file descriptor table and
478 * shared process leaders.
479 */
480 fdtol = p1->p_fdtol;
481 fdtol->fdl_refcount++;
482 } else {
483 /*
484 * Shared file descriptor table, and
485 * different process leaders
486 */
487 fdtol = filedesc_to_leader_alloc(p1->p_fdtol, p2);
488 }
489 }
490 p2->p_fdtol = fdtol;
491 p2->p_limit = plimit_fork(p1);
492
493 /*
494 * Preserve some more flags in subprocess. P_PROFIL has already
495 * been preserved.
496 */
497 p2->p_flags |= p1->p_flags & P_SUGID;
498 if (p1->p_session->s_ttyvp != NULL && (p1->p_flags & P_CONTROLT))
499 p2->p_flags |= P_CONTROLT;
500 if (flags & RFPPWAIT)
501 p2->p_flags |= P_PPWAIT;
502
503 /*
504 * Inherit the virtual kernel structure (allows a virtual kernel
505 * to fork to simulate multiple cpus).
506 */
507 if (p1->p_vkernel)
508 vkernel_inherit(p1, p2);
509
510 /*
511 * Once we are on a pglist we may receive signals. XXX we might
512 * race a ^C being sent to the process group by not receiving it
513 * at all prior to this line.
514 */
515 pgref(p1grp);
516 lwkt_gettoken(&p1grp->pg_token);
517 LIST_INSERT_AFTER(p1, p2, p_pglist);
518 lwkt_reltoken(&p1grp->pg_token);
519
520 /*
521 * Attach the new process to its parent.
522 *
523 * If RFNOWAIT is set, the newly created process becomes a child
524 * of init. This effectively disassociates the child from the
525 * parent.
526 */
527 if (flags & RFNOWAIT)
528 pptr = initproc;
529 else
530 pptr = p1;
531 p2->p_pptr = pptr;
532 LIST_INIT(&p2->p_children);
533
534 lwkt_gettoken(&pptr->p_token);
535 LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
536 lwkt_reltoken(&pptr->p_token);
537
538 varsymset_init(&p2->p_varsymset, &p1->p_varsymset);
539 callout_init_mp(&p2->p_ithandle);
540
541 #ifdef KTRACE
542 /*
543 * Copy traceflag and tracefile if enabled. If not inherited,
544 * these were zeroed above but we still could have a trace race
545 * so make sure p2's p_tracenode is NULL.
546 */
547 if ((p1->p_traceflag & KTRFAC_INHERIT) && p2->p_tracenode == NULL) {
548 p2->p_traceflag = p1->p_traceflag;
549 p2->p_tracenode = ktrinherit(p1->p_tracenode);
550 }
551 #endif
552
553 /*
554 * This begins the section where we must prevent the parent
555 * from being swapped.
556 *
557 * Gets PRELE'd in the caller in start_forked_proc().
558 */
559 PHOLD(p1);
560
561 vm_fork(p1, p2, flags);
562
563 /*
564 * Create the first lwp associated with the new proc.
565 * It will return via a different execution path later, directly
566 * into userland, after it was put on the runq by
567 * start_forked_proc().
568 */
569 lwp_fork(lp1, p2, flags);
570
571 if (flags == (RFFDG | RFPROC | RFPGLOCK)) {
572 mycpu->gd_cnt.v_forks++;
573 mycpu->gd_cnt.v_forkpages += p2->p_vmspace->vm_dsize +
574 p2->p_vmspace->vm_ssize;
575 } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM | RFPGLOCK)) {
576 mycpu->gd_cnt.v_vforks++;
577 mycpu->gd_cnt.v_vforkpages += p2->p_vmspace->vm_dsize +
578 p2->p_vmspace->vm_ssize;
579 } else if (p1 == &proc0) {
580 mycpu->gd_cnt.v_kthreads++;
581 mycpu->gd_cnt.v_kthreadpages += p2->p_vmspace->vm_dsize +
582 p2->p_vmspace->vm_ssize;
583 } else {
584 mycpu->gd_cnt.v_rforks++;
585 mycpu->gd_cnt.v_rforkpages += p2->p_vmspace->vm_dsize +
586 p2->p_vmspace->vm_ssize;
587 }
588
589 /*
590 * Both processes are set up, now check if any loadable modules want
591 * to adjust anything.
592 * What if they have an error? XXX
593 */
594 TAILQ_FOREACH(ep, &fork_list, next) {
595 (*ep->function)(p1, p2, flags);
596 }
597
598 /*
599 * Set the start time. Note that the process is not runnable. The
600 * caller is responsible for making it runnable.
601 */
602 microtime(&p2->p_start);
603 p2->p_acflag = AFORK;
604
605 /*
606 * tell any interested parties about the new process
607 */
608 KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid);
609
610 /*
611 * Return child proc pointer to parent.
612 */
613 *procp = p2;
614 error = 0;
615 done:
616 if (p2)
617 lwkt_reltoken(&p2->p_token);
618 lwkt_reltoken(&p1->p_token);
619 if (plkgrp) {
620 lockmgr(&plkgrp->pg_lock, LK_RELEASE);
621 pgrel(plkgrp);
622 }
623 return (error);
624 }
625
626 static struct lwp *
627 lwp_fork(struct lwp *origlp, struct proc *destproc, int flags)
628 {
629 globaldata_t gd = mycpu;
630 struct lwp *lp;
631 struct thread *td;
632
633 lp = kmalloc(sizeof(struct lwp), M_LWP, M_WAITOK|M_ZERO);
634
635 lp->lwp_proc = destproc;
636 lp->lwp_vmspace = destproc->p_vmspace;
637 lp->lwp_stat = LSRUN;
638 bcopy(&origlp->lwp_startcopy, &lp->lwp_startcopy,
639 (unsigned) ((caddr_t)&lp->lwp_endcopy -
640 (caddr_t)&lp->lwp_startcopy));
641 lp->lwp_flags |= origlp->lwp_flags & LWP_ALTSTACK;
642 /*
643 * Set cpbase to the last timeout that occured (not the upcoming
644 * timeout).
645 *
646 * A critical section is required since a timer IPI can update
647 * scheduler specific data.
648 */
649 crit_enter();
650 lp->lwp_cpbase = gd->gd_schedclock.time - gd->gd_schedclock.periodic;
651 destproc->p_usched->heuristic_forking(origlp, lp);
652 crit_exit();
653 lp->lwp_cpumask &= usched_mastermask;
654 lwkt_token_init(&lp->lwp_token, "lwp_token");
655 spin_init(&lp->lwp_spin);
656
657 /*
658 * Assign the thread to the current cpu to begin with so we
659 * can manipulate it.
660 */
661 td = lwkt_alloc_thread(NULL, LWKT_THREAD_STACK, gd->gd_cpuid, 0);
662 lp->lwp_thread = td;
663 td->td_ucred = crhold(destproc->p_ucred);
664 td->td_proc = destproc;
665 td->td_lwp = lp;
666 td->td_switch = cpu_heavy_switch;
667 #ifdef NO_LWKT_SPLIT_USERPRI
668 lwkt_setpri(td, TDPRI_USER_NORM);
669 #else
670 lwkt_setpri(td, TDPRI_KERN_USER);
671 #endif
672 lwkt_set_comm(td, "%s", destproc->p_comm);
673
674 /*
675 * cpu_fork will copy and update the pcb, set up the kernel stack,
676 * and make the child ready to run.
677 */
678 cpu_fork(origlp, lp, flags);
679 kqueue_init(&lp->lwp_kqueue, destproc->p_fd);
680
681 /*
682 * Assign a TID to the lp. Loop until the insert succeeds (returns
683 * NULL).
684 */
685 lp->lwp_tid = destproc->p_lasttid;
686 do {
687 if (++lp->lwp_tid < 0)
688 lp->lwp_tid = 1;
689 } while (lwp_rb_tree_RB_INSERT(&destproc->p_lwp_tree, lp) != NULL);
690 destproc->p_lasttid = lp->lwp_tid;
691 destproc->p_nthreads++;
692
693 /*
694 * This flag is set and never cleared. It means that the process
695 * was threaded at some point. Used to improve exit performance.
696 */
697 destproc->p_flags |= P_MAYBETHREADED;
698
699 return (lp);
700 }
701
702 /*
703 * The next two functionms are general routines to handle adding/deleting
704 * items on the fork callout list.
705 *
706 * at_fork():
707 * Take the arguments given and put them onto the fork callout list,
708 * However first make sure that it's not already there.
709 * Returns 0 on success or a standard error number.
710 */
711 int
712 at_fork(forklist_fn function)
713 {
714 struct forklist *ep;
715
716 #ifdef INVARIANTS
717 /* let the programmer know if he's been stupid */
718 if (rm_at_fork(function)) {
719 kprintf("WARNING: fork callout entry (%p) already present\n",
720 function);
721 }
722 #endif
723 ep = kmalloc(sizeof(*ep), M_ATFORK, M_WAITOK|M_ZERO);
724 ep->function = function;
725 TAILQ_INSERT_TAIL(&fork_list, ep, next);
726 return (0);
727 }
728
729 /*
730 * Scan the exit callout list for the given item and remove it..
731 * Returns the number of items removed (0 or 1)
732 */
733 int
734 rm_at_fork(forklist_fn function)
735 {
736 struct forklist *ep;
737
738 TAILQ_FOREACH(ep, &fork_list, next) {
739 if (ep->function == function) {
740 TAILQ_REMOVE(&fork_list, ep, next);
741 kfree(ep, M_ATFORK);
742 return(1);
743 }
744 }
745 return (0);
746 }
747
748 /*
749 * Add a forked process to the run queue after any remaining setup, such
750 * as setting the fork handler, has been completed.
751 *
752 * p2 is held by the caller.
753 */
754 void
755 start_forked_proc(struct lwp *lp1, struct proc *p2)
756 {
757 struct lwp *lp2 = ONLY_LWP_IN_PROC(p2);
758 int pflags;
759
760 /*
761 * Move from SIDL to RUN queue, and activate the process's thread.
762 * Activation of the thread effectively makes the process "a"
763 * current process, so we do not setrunqueue().
764 *
765 * YYY setrunqueue works here but we should clean up the trampoline
766 * code so we just schedule the LWKT thread and let the trampoline
767 * deal with the userland scheduler on return to userland.
768 */
769 KASSERT(p2->p_stat == SIDL,
770 ("cannot start forked process, bad status: %p", p2));
771 p2->p_usched->resetpriority(lp2);
772 crit_enter();
773 p2->p_stat = SACTIVE;
774 lp2->lwp_stat = LSRUN;
775 p2->p_usched->setrunqueue(lp2);
776 crit_exit();
777
778 /*
779 * Now can be swapped.
780 */
781 PRELE(lp1->lwp_proc);
782
783 /*
784 * Preserve synchronization semantics of vfork. P_PPWAIT is set in
785 * the child until it has retired the parent's resources. The parent
786 * must wait for the flag to be cleared by the child.
787 *
788 * Interlock the flag/tsleep with atomic ops to avoid unnecessary
789 * p_token conflicts.
790 *
791 * XXX Is this use of an atomic op on a field that is not normally
792 * manipulated with atomic ops ok?
793 */
794 while ((pflags = p2->p_flags) & P_PPWAIT) {
795 cpu_ccfence();
796 tsleep_interlock(lp1->lwp_proc, 0);
797 if (atomic_cmpset_int(&p2->p_flags, pflags, pflags))
798 tsleep(lp1->lwp_proc, PINTERLOCKED, "ppwait", 0);
799 }
800 }
Cache object: 11e4c21fe8a614e32e1c99f78ef30c59
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