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 * 4. 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 */
36
37 #include <sys/cdefs.h>
38 __FBSDID("$FreeBSD: releng/6.0/sys/kern/kern_fork.c 147730 2005-07-01 16:28:32Z ssouhlal $");
39
40 #include "opt_ktrace.h"
41 #include "opt_mac.h"
42
43 #include <sys/param.h>
44 #include <sys/systm.h>
45 #include <sys/sysproto.h>
46 #include <sys/eventhandler.h>
47 #include <sys/filedesc.h>
48 #include <sys/kernel.h>
49 #include <sys/kthread.h>
50 #include <sys/sysctl.h>
51 #include <sys/lock.h>
52 #include <sys/malloc.h>
53 #include <sys/mutex.h>
54 #include <sys/proc.h>
55 #include <sys/pioctl.h>
56 #include <sys/resourcevar.h>
57 #include <sys/sched.h>
58 #include <sys/syscall.h>
59 #include <sys/vmmeter.h>
60 #include <sys/vnode.h>
61 #include <sys/acct.h>
62 #include <sys/mac.h>
63 #include <sys/ktr.h>
64 #include <sys/ktrace.h>
65 #include <sys/unistd.h>
66 #include <sys/sx.h>
67 #include <sys/signalvar.h>
68
69 #include <vm/vm.h>
70 #include <vm/pmap.h>
71 #include <vm/vm_map.h>
72 #include <vm/vm_extern.h>
73 #include <vm/uma.h>
74
75
76 #ifndef _SYS_SYSPROTO_H_
77 struct fork_args {
78 int dummy;
79 };
80 #endif
81
82 static int forksleep; /* Place for fork1() to sleep on. */
83
84 /*
85 * MPSAFE
86 */
87 /* ARGSUSED */
88 int
89 fork(td, uap)
90 struct thread *td;
91 struct fork_args *uap;
92 {
93 int error;
94 struct proc *p2;
95
96 error = fork1(td, RFFDG | RFPROC, 0, &p2);
97 if (error == 0) {
98 td->td_retval[0] = p2->p_pid;
99 td->td_retval[1] = 0;
100 }
101 return (error);
102 }
103
104 /*
105 * MPSAFE
106 */
107 /* ARGSUSED */
108 int
109 vfork(td, uap)
110 struct thread *td;
111 struct vfork_args *uap;
112 {
113 int error;
114 struct proc *p2;
115
116 error = fork1(td, RFFDG | RFPROC | RFPPWAIT | RFMEM, 0, &p2);
117 if (error == 0) {
118 td->td_retval[0] = p2->p_pid;
119 td->td_retval[1] = 0;
120 }
121 return (error);
122 }
123
124 /*
125 * MPSAFE
126 */
127 int
128 rfork(td, uap)
129 struct thread *td;
130 struct rfork_args *uap;
131 {
132 struct proc *p2;
133 int error;
134
135 /* Don't allow kernel-only flags. */
136 if ((uap->flags & RFKERNELONLY) != 0)
137 return (EINVAL);
138
139 error = fork1(td, uap->flags, 0, &p2);
140 if (error == 0) {
141 td->td_retval[0] = p2 ? p2->p_pid : 0;
142 td->td_retval[1] = 0;
143 }
144 return (error);
145 }
146
147 int nprocs = 1; /* process 0 */
148 int lastpid = 0;
149 SYSCTL_INT(_kern, OID_AUTO, lastpid, CTLFLAG_RD, &lastpid, 0,
150 "Last used PID");
151
152 /*
153 * Random component to lastpid generation. We mix in a random factor to make
154 * it a little harder to predict. We sanity check the modulus value to avoid
155 * doing it in critical paths. Don't let it be too small or we pointlessly
156 * waste randomness entropy, and don't let it be impossibly large. Using a
157 * modulus that is too big causes a LOT more process table scans and slows
158 * down fork processing as the pidchecked caching is defeated.
159 */
160 static int randompid = 0;
161
162 static int
163 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
164 {
165 int error, pid;
166
167 error = sysctl_wire_old_buffer(req, sizeof(int));
168 if (error != 0)
169 return(error);
170 sx_xlock(&allproc_lock);
171 pid = randompid;
172 error = sysctl_handle_int(oidp, &pid, 0, req);
173 if (error == 0 && req->newptr != NULL) {
174 if (pid < 0 || pid > PID_MAX - 100) /* out of range */
175 pid = PID_MAX - 100;
176 else if (pid < 2) /* NOP */
177 pid = 0;
178 else if (pid < 100) /* Make it reasonable */
179 pid = 100;
180 randompid = pid;
181 }
182 sx_xunlock(&allproc_lock);
183 return (error);
184 }
185
186 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
187 0, 0, sysctl_kern_randompid, "I", "Random PID modulus");
188
189 int
190 fork1(td, flags, pages, procp)
191 struct thread *td;
192 int flags;
193 int pages;
194 struct proc **procp;
195 {
196 struct proc *p1, *p2, *pptr;
197 uid_t uid;
198 struct proc *newproc;
199 int ok, trypid;
200 static int curfail, pidchecked = 0;
201 static struct timeval lastfail;
202 struct filedesc *fd;
203 struct filedesc_to_leader *fdtol;
204 struct thread *td2;
205 struct ksegrp *kg2;
206 struct sigacts *newsigacts;
207 int error;
208
209 /* Can't copy and clear. */
210 if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
211 return (EINVAL);
212
213 p1 = td->td_proc;
214
215 /*
216 * Here we don't create a new process, but we divorce
217 * certain parts of a process from itself.
218 */
219 if ((flags & RFPROC) == 0) {
220 vm_forkproc(td, NULL, NULL, flags);
221
222 /*
223 * Close all file descriptors.
224 */
225 if (flags & RFCFDG) {
226 struct filedesc *fdtmp;
227 fdtmp = fdinit(td->td_proc->p_fd);
228 fdfree(td);
229 p1->p_fd = fdtmp;
230 }
231
232 /*
233 * Unshare file descriptors (from parent).
234 */
235 if (flags & RFFDG)
236 fdunshare(p1, td);
237 *procp = NULL;
238 return (0);
239 }
240
241 /*
242 * Note 1:1 allows for forking with one thread coming out on the
243 * other side with the expectation that the process is about to
244 * exec.
245 */
246 if (p1->p_flag & P_HADTHREADS) {
247 /*
248 * Idle the other threads for a second.
249 * Since the user space is copied, it must remain stable.
250 * In addition, all threads (from the user perspective)
251 * need to either be suspended or in the kernel,
252 * where they will try restart in the parent and will
253 * be aborted in the child.
254 */
255 PROC_LOCK(p1);
256 if (thread_single(SINGLE_NO_EXIT)) {
257 /* Abort. Someone else is single threading before us. */
258 PROC_UNLOCK(p1);
259 return (ERESTART);
260 }
261 PROC_UNLOCK(p1);
262 /*
263 * All other activity in this process
264 * is now suspended at the user boundary,
265 * (or other safe places if we think of any).
266 */
267 }
268
269 /* Allocate new proc. */
270 newproc = uma_zalloc(proc_zone, M_WAITOK);
271 #ifdef MAC
272 mac_init_proc(newproc);
273 #endif
274 knlist_init(&newproc->p_klist, &newproc->p_mtx, NULL, NULL, NULL);
275
276 /* We have to lock the process tree while we look for a pid. */
277 sx_slock(&proctree_lock);
278
279 /*
280 * Although process entries are dynamically created, we still keep
281 * a global limit on the maximum number we will create. Don't allow
282 * a nonprivileged user to use the last ten processes; don't let root
283 * exceed the limit. The variable nprocs is the current number of
284 * processes, maxproc is the limit.
285 */
286 sx_xlock(&allproc_lock);
287 uid = td->td_ucred->cr_ruid;
288 if ((nprocs >= maxproc - 10 &&
289 suser_cred(td->td_ucred, SUSER_RUID) != 0) ||
290 nprocs >= maxproc) {
291 error = EAGAIN;
292 goto fail;
293 }
294
295 /*
296 * Increment the count of procs running with this uid. Don't allow
297 * a nonprivileged user to exceed their current limit.
298 */
299 PROC_LOCK(p1);
300 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1,
301 (uid != 0) ? lim_cur(p1, RLIMIT_NPROC) : 0);
302 PROC_UNLOCK(p1);
303 if (!ok) {
304 error = EAGAIN;
305 goto fail;
306 }
307
308 /*
309 * Increment the nprocs resource before blocking can occur. There
310 * are hard-limits as to the number of processes that can run.
311 */
312 nprocs++;
313
314 /*
315 * Find an unused process ID. We remember a range of unused IDs
316 * ready to use (from lastpid+1 through pidchecked-1).
317 *
318 * If RFHIGHPID is set (used during system boot), do not allocate
319 * low-numbered pids.
320 */
321 trypid = lastpid + 1;
322 if (flags & RFHIGHPID) {
323 if (trypid < 10)
324 trypid = 10;
325 } else {
326 if (randompid)
327 trypid += arc4random() % randompid;
328 }
329 retry:
330 /*
331 * If the process ID prototype has wrapped around,
332 * restart somewhat above 0, as the low-numbered procs
333 * tend to include daemons that don't exit.
334 */
335 if (trypid >= PID_MAX) {
336 trypid = trypid % PID_MAX;
337 if (trypid < 100)
338 trypid += 100;
339 pidchecked = 0;
340 }
341 if (trypid >= pidchecked) {
342 int doingzomb = 0;
343
344 pidchecked = PID_MAX;
345 /*
346 * Scan the active and zombie procs to check whether this pid
347 * is in use. Remember the lowest pid that's greater
348 * than trypid, so we can avoid checking for a while.
349 */
350 p2 = LIST_FIRST(&allproc);
351 again:
352 for (; p2 != NULL; p2 = LIST_NEXT(p2, p_list)) {
353 PROC_LOCK(p2);
354 while (p2->p_pid == trypid ||
355 (p2->p_pgrp != NULL &&
356 (p2->p_pgrp->pg_id == trypid ||
357 (p2->p_session != NULL &&
358 p2->p_session->s_sid == trypid)))) {
359 trypid++;
360 if (trypid >= pidchecked) {
361 PROC_UNLOCK(p2);
362 goto retry;
363 }
364 }
365 if (p2->p_pid > trypid && pidchecked > p2->p_pid)
366 pidchecked = p2->p_pid;
367 if (p2->p_pgrp != NULL) {
368 if (p2->p_pgrp->pg_id > trypid &&
369 pidchecked > p2->p_pgrp->pg_id)
370 pidchecked = p2->p_pgrp->pg_id;
371 if (p2->p_session != NULL &&
372 p2->p_session->s_sid > trypid &&
373 pidchecked > p2->p_session->s_sid)
374 pidchecked = p2->p_session->s_sid;
375 }
376 PROC_UNLOCK(p2);
377 }
378 if (!doingzomb) {
379 doingzomb = 1;
380 p2 = LIST_FIRST(&zombproc);
381 goto again;
382 }
383 }
384 sx_sunlock(&proctree_lock);
385
386 /*
387 * RFHIGHPID does not mess with the lastpid counter during boot.
388 */
389 if (flags & RFHIGHPID)
390 pidchecked = 0;
391 else
392 lastpid = trypid;
393
394 p2 = newproc;
395 p2->p_state = PRS_NEW; /* protect against others */
396 p2->p_pid = trypid;
397 LIST_INSERT_HEAD(&allproc, p2, p_list);
398 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
399 sx_xunlock(&allproc_lock);
400
401 /*
402 * Malloc things while we don't hold any locks.
403 */
404 if (flags & RFSIGSHARE)
405 newsigacts = NULL;
406 else
407 newsigacts = sigacts_alloc();
408
409 /*
410 * Copy filedesc.
411 */
412 if (flags & RFCFDG) {
413 fd = fdinit(p1->p_fd);
414 fdtol = NULL;
415 } else if (flags & RFFDG) {
416 fd = fdcopy(p1->p_fd);
417 fdtol = NULL;
418 } else {
419 fd = fdshare(p1->p_fd);
420 if (p1->p_fdtol == NULL)
421 p1->p_fdtol =
422 filedesc_to_leader_alloc(NULL,
423 NULL,
424 p1->p_leader);
425 if ((flags & RFTHREAD) != 0) {
426 /*
427 * Shared file descriptor table and
428 * shared process leaders.
429 */
430 fdtol = p1->p_fdtol;
431 FILEDESC_LOCK_FAST(p1->p_fd);
432 fdtol->fdl_refcount++;
433 FILEDESC_UNLOCK_FAST(p1->p_fd);
434 } else {
435 /*
436 * Shared file descriptor table, and
437 * different process leaders
438 */
439 fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
440 p1->p_fd,
441 p2);
442 }
443 }
444 /*
445 * Make a proc table entry for the new process.
446 * Start by zeroing the section of proc that is zero-initialized,
447 * then copy the section that is copied directly from the parent.
448 */
449 td2 = FIRST_THREAD_IN_PROC(p2);
450 kg2 = FIRST_KSEGRP_IN_PROC(p2);
451
452 /* Allocate and switch to an alternate kstack if specified. */
453 if (pages != 0)
454 vm_thread_new_altkstack(td2, pages);
455
456 PROC_LOCK(p2);
457 PROC_LOCK(p1);
458
459 bzero(&p2->p_startzero,
460 __rangeof(struct proc, p_startzero, p_endzero));
461 bzero(&td2->td_startzero,
462 __rangeof(struct thread, td_startzero, td_endzero));
463 bzero(&kg2->kg_startzero,
464 __rangeof(struct ksegrp, kg_startzero, kg_endzero));
465
466 bcopy(&p1->p_startcopy, &p2->p_startcopy,
467 __rangeof(struct proc, p_startcopy, p_endcopy));
468 bcopy(&td->td_startcopy, &td2->td_startcopy,
469 __rangeof(struct thread, td_startcopy, td_endcopy));
470 bcopy(&td->td_ksegrp->kg_startcopy, &kg2->kg_startcopy,
471 __rangeof(struct ksegrp, kg_startcopy, kg_endcopy));
472
473 td2->td_sigstk = td->td_sigstk;
474 td2->td_sigmask = td->td_sigmask;
475
476 /*
477 * Duplicate sub-structures as needed.
478 * Increase reference counts on shared objects.
479 */
480 p2->p_flag = 0;
481 if (p1->p_flag & P_PROFIL)
482 startprofclock(p2);
483 mtx_lock_spin(&sched_lock);
484 p2->p_sflag = PS_INMEM;
485 /*
486 * Allow the scheduler to adjust the priority of the child and
487 * parent while we hold the sched_lock.
488 */
489 sched_fork(td, td2);
490
491 mtx_unlock_spin(&sched_lock);
492 p2->p_ucred = crhold(td->td_ucred);
493 td2->td_ucred = crhold(p2->p_ucred); /* XXXKSE */
494
495 pargs_hold(p2->p_args);
496
497 if (flags & RFSIGSHARE) {
498 p2->p_sigacts = sigacts_hold(p1->p_sigacts);
499 } else {
500 sigacts_copy(newsigacts, p1->p_sigacts);
501 p2->p_sigacts = newsigacts;
502 }
503 if (flags & RFLINUXTHPN)
504 p2->p_sigparent = SIGUSR1;
505 else
506 p2->p_sigparent = SIGCHLD;
507
508 p2->p_textvp = p1->p_textvp;
509 p2->p_fd = fd;
510 p2->p_fdtol = fdtol;
511
512 /*
513 * p_limit is copy-on-write. Bump its refcount.
514 */
515 p2->p_limit = lim_hold(p1->p_limit);
516
517 pstats_fork(p1->p_stats, p2->p_stats);
518
519 PROC_UNLOCK(p1);
520 PROC_UNLOCK(p2);
521
522 /* Bump references to the text vnode (for procfs) */
523 if (p2->p_textvp)
524 vref(p2->p_textvp);
525
526 /*
527 * Set up linkage for kernel based threading.
528 */
529 if ((flags & RFTHREAD) != 0) {
530 mtx_lock(&ppeers_lock);
531 p2->p_peers = p1->p_peers;
532 p1->p_peers = p2;
533 p2->p_leader = p1->p_leader;
534 mtx_unlock(&ppeers_lock);
535 PROC_LOCK(p1->p_leader);
536 if ((p1->p_leader->p_flag & P_WEXIT) != 0) {
537 PROC_UNLOCK(p1->p_leader);
538 /*
539 * The task leader is exiting, so process p1 is
540 * going to be killed shortly. Since p1 obviously
541 * isn't dead yet, we know that the leader is either
542 * sending SIGKILL's to all the processes in this
543 * task or is sleeping waiting for all the peers to
544 * exit. We let p1 complete the fork, but we need
545 * to go ahead and kill the new process p2 since
546 * the task leader may not get a chance to send
547 * SIGKILL to it. We leave it on the list so that
548 * the task leader will wait for this new process
549 * to commit suicide.
550 */
551 PROC_LOCK(p2);
552 psignal(p2, SIGKILL);
553 PROC_UNLOCK(p2);
554 } else
555 PROC_UNLOCK(p1->p_leader);
556 } else {
557 p2->p_peers = NULL;
558 p2->p_leader = p2;
559 }
560
561 sx_xlock(&proctree_lock);
562 PGRP_LOCK(p1->p_pgrp);
563 PROC_LOCK(p2);
564 PROC_LOCK(p1);
565
566 /*
567 * Preserve some more flags in subprocess. P_PROFIL has already
568 * been preserved.
569 */
570 p2->p_flag |= p1->p_flag & P_SUGID;
571 td2->td_pflags |= td->td_pflags & TDP_ALTSTACK;
572 SESS_LOCK(p1->p_session);
573 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
574 p2->p_flag |= P_CONTROLT;
575 SESS_UNLOCK(p1->p_session);
576 if (flags & RFPPWAIT)
577 p2->p_flag |= P_PPWAIT;
578
579 p2->p_pgrp = p1->p_pgrp;
580 LIST_INSERT_AFTER(p1, p2, p_pglist);
581 PGRP_UNLOCK(p1->p_pgrp);
582 LIST_INIT(&p2->p_children);
583
584 callout_init(&p2->p_itcallout, CALLOUT_MPSAFE);
585
586 #ifdef KTRACE
587 /*
588 * Copy traceflag and tracefile if enabled.
589 */
590 mtx_lock(&ktrace_mtx);
591 KASSERT(p2->p_tracevp == NULL, ("new process has a ktrace vnode"));
592 if (p1->p_traceflag & KTRFAC_INHERIT) {
593 p2->p_traceflag = p1->p_traceflag;
594 if ((p2->p_tracevp = p1->p_tracevp) != NULL) {
595 VREF(p2->p_tracevp);
596 KASSERT(p1->p_tracecred != NULL,
597 ("ktrace vnode with no cred"));
598 p2->p_tracecred = crhold(p1->p_tracecred);
599 }
600 }
601 mtx_unlock(&ktrace_mtx);
602 #endif
603
604 /*
605 * If PF_FORK is set, the child process inherits the
606 * procfs ioctl flags from its parent.
607 */
608 if (p1->p_pfsflags & PF_FORK) {
609 p2->p_stops = p1->p_stops;
610 p2->p_pfsflags = p1->p_pfsflags;
611 }
612
613 /*
614 * This begins the section where we must prevent the parent
615 * from being swapped.
616 */
617 _PHOLD(p1);
618 PROC_UNLOCK(p1);
619
620 /*
621 * Attach the new process to its parent.
622 *
623 * If RFNOWAIT is set, the newly created process becomes a child
624 * of init. This effectively disassociates the child from the
625 * parent.
626 */
627 if (flags & RFNOWAIT)
628 pptr = initproc;
629 else
630 pptr = p1;
631 p2->p_pptr = pptr;
632 LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
633 sx_xunlock(&proctree_lock);
634
635 /* Inform accounting that we have forked. */
636 p2->p_acflag = AFORK;
637 PROC_UNLOCK(p2);
638
639 /*
640 * Finish creating the child process. It will return via a different
641 * execution path later. (ie: directly into user mode)
642 */
643 vm_forkproc(td, p2, td2, flags);
644
645 if (flags == (RFFDG | RFPROC)) {
646 atomic_add_int(&cnt.v_forks, 1);
647 atomic_add_int(&cnt.v_forkpages, p2->p_vmspace->vm_dsize +
648 p2->p_vmspace->vm_ssize);
649 } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
650 atomic_add_int(&cnt.v_vforks, 1);
651 atomic_add_int(&cnt.v_vforkpages, p2->p_vmspace->vm_dsize +
652 p2->p_vmspace->vm_ssize);
653 } else if (p1 == &proc0) {
654 atomic_add_int(&cnt.v_kthreads, 1);
655 atomic_add_int(&cnt.v_kthreadpages, p2->p_vmspace->vm_dsize +
656 p2->p_vmspace->vm_ssize);
657 } else {
658 atomic_add_int(&cnt.v_rforks, 1);
659 atomic_add_int(&cnt.v_rforkpages, p2->p_vmspace->vm_dsize +
660 p2->p_vmspace->vm_ssize);
661 }
662
663 /*
664 * Both processes are set up, now check if any loadable modules want
665 * to adjust anything.
666 * What if they have an error? XXX
667 */
668 EVENTHANDLER_INVOKE(process_fork, p1, p2, flags);
669
670 /*
671 * Set the child start time and mark the process as being complete.
672 */
673 microuptime(&p2->p_stats->p_start);
674 mtx_lock_spin(&sched_lock);
675 p2->p_state = PRS_NORMAL;
676
677 /*
678 * If RFSTOPPED not requested, make child runnable and add to
679 * run queue.
680 */
681 if ((flags & RFSTOPPED) == 0) {
682 TD_SET_CAN_RUN(td2);
683 setrunqueue(td2, SRQ_BORING);
684 }
685 mtx_unlock_spin(&sched_lock);
686
687 /*
688 * Now can be swapped.
689 */
690 PROC_LOCK(p1);
691 _PRELE(p1);
692
693 /*
694 * Tell any interested parties about the new process.
695 */
696 KNOTE_LOCKED(&p1->p_klist, NOTE_FORK | p2->p_pid);
697
698 PROC_UNLOCK(p1);
699
700 /*
701 * Preserve synchronization semantics of vfork. If waiting for
702 * child to exec or exit, set P_PPWAIT on child, and sleep on our
703 * proc (in case of exit).
704 */
705 PROC_LOCK(p2);
706 while (p2->p_flag & P_PPWAIT)
707 msleep(p1, &p2->p_mtx, PWAIT, "ppwait", 0);
708 PROC_UNLOCK(p2);
709
710 /*
711 * If other threads are waiting, let them continue now.
712 */
713 if (p1->p_flag & P_HADTHREADS) {
714 PROC_LOCK(p1);
715 thread_single_end();
716 PROC_UNLOCK(p1);
717 }
718
719 /*
720 * Return child proc pointer to parent.
721 */
722 *procp = p2;
723 return (0);
724 fail:
725 sx_sunlock(&proctree_lock);
726 if (ppsratecheck(&lastfail, &curfail, 1))
727 printf("maxproc limit exceeded by uid %i, please see tuning(7) and login.conf(5).\n",
728 uid);
729 sx_xunlock(&allproc_lock);
730 #ifdef MAC
731 mac_destroy_proc(newproc);
732 #endif
733 uma_zfree(proc_zone, newproc);
734 if (p1->p_flag & P_HADTHREADS) {
735 PROC_LOCK(p1);
736 thread_single_end();
737 PROC_UNLOCK(p1);
738 }
739 tsleep(&forksleep, PUSER, "fork", hz / 2);
740 return (error);
741 }
742
743 /*
744 * Handle the return of a child process from fork1(). This function
745 * is called from the MD fork_trampoline() entry point.
746 */
747 void
748 fork_exit(callout, arg, frame)
749 void (*callout)(void *, struct trapframe *);
750 void *arg;
751 struct trapframe *frame;
752 {
753 struct proc *p;
754 struct thread *td;
755
756 /*
757 * Finish setting up thread glue so that it begins execution in a
758 * non-nested critical section with sched_lock held but not recursed.
759 */
760 td = curthread;
761 p = td->td_proc;
762 td->td_oncpu = PCPU_GET(cpuid);
763 KASSERT(p->p_state == PRS_NORMAL, ("executing process is still new"));
764
765 sched_lock.mtx_lock = (uintptr_t)td;
766 mtx_assert(&sched_lock, MA_OWNED | MA_NOTRECURSED);
767 CTR4(KTR_PROC, "fork_exit: new thread %p (kse %p, pid %d, %s)",
768 td, td->td_sched, p->p_pid, p->p_comm);
769
770 /*
771 * Processes normally resume in mi_switch() after being
772 * cpu_switch()'ed to, but when children start up they arrive here
773 * instead, so we must do much the same things as mi_switch() would.
774 */
775
776 if ((td = PCPU_GET(deadthread))) {
777 PCPU_SET(deadthread, NULL);
778 thread_stash(td);
779 }
780 td = curthread;
781 mtx_unlock_spin(&sched_lock);
782
783 /*
784 * cpu_set_fork_handler intercepts this function call to
785 * have this call a non-return function to stay in kernel mode.
786 * initproc has its own fork handler, but it does return.
787 */
788 KASSERT(callout != NULL, ("NULL callout in fork_exit"));
789 callout(arg, frame);
790
791 /*
792 * Check if a kernel thread misbehaved and returned from its main
793 * function.
794 */
795 PROC_LOCK(p);
796 if (p->p_flag & P_KTHREAD) {
797 PROC_UNLOCK(p);
798 printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
799 p->p_comm, p->p_pid);
800 kthread_exit(0);
801 }
802 PROC_UNLOCK(p);
803 mtx_assert(&Giant, MA_NOTOWNED);
804 }
805
806 /*
807 * Simplified back end of syscall(), used when returning from fork()
808 * directly into user mode. Giant is not held on entry, and must not
809 * be held on return. This function is passed in to fork_exit() as the
810 * first parameter and is called when returning to a new userland process.
811 */
812 void
813 fork_return(td, frame)
814 struct thread *td;
815 struct trapframe *frame;
816 {
817
818 userret(td, frame, 0);
819 #ifdef KTRACE
820 if (KTRPOINT(td, KTR_SYSRET))
821 ktrsysret(SYS_fork, 0, 0);
822 #endif
823 mtx_assert(&Giant, MA_NOTOWNED);
824 }
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