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.
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
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
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22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * @(#)kern_fork.c 8.6 (Berkeley) 4/8/94
37 #include <sys/cdefs.h>
38 __FBSDID("$FreeBSD$");
40 #include "opt_ktrace.h"
41 #include "opt_kstack_pages.h"
43 #include <sys/param.h>
44 #include <sys/systm.h>
45 #include <sys/sysproto.h>
46 #include <sys/eventhandler.h>
47 #include <sys/fcntl.h>
48 #include <sys/filedesc.h>
50 #include <sys/kernel.h>
51 #include <sys/kthread.h>
52 #include <sys/sysctl.h>
54 #include <sys/malloc.h>
55 #include <sys/mutex.h>
58 #include <sys/procdesc.h>
59 #include <sys/pioctl.h>
60 #include <sys/racct.h>
61 #include <sys/resourcevar.h>
62 #include <sys/sched.h>
63 #include <sys/syscall.h>
64 #include <sys/vmmeter.h>
65 #include <sys/vnode.h>
68 #include <sys/ktrace.h>
69 #include <sys/unistd.h>
72 #include <sys/sysent.h>
73 #include <sys/signalvar.h>
75 #include <security/audit/audit.h>
76 #include <security/mac/mac_framework.h>
80 #include <vm/vm_map.h>
81 #include <vm/vm_extern.h>
85 #include <sys/dtrace_bsd.h>
86 dtrace_fork_func_t dtrace_fasttrap_fork;
89 SDT_PROVIDER_DECLARE(proc);
90 SDT_PROBE_DEFINE3(proc, kernel, , create, "struct proc *",
91 "struct proc *", "int");
93 #ifndef _SYS_SYSPROTO_H_
101 sys_fork(struct thread *td, struct fork_args *uap)
106 error = fork1(td, RFFDG | RFPROC, 0, &p2, NULL, 0);
108 td->td_retval[0] = p2->p_pid;
109 td->td_retval[1] = 0;
118 struct pdfork_args *uap;
124 * It is necessary to return fd by reference because 0 is a valid file
125 * descriptor number, and the child needs to be able to distinguish
126 * itself from the parent using the return value.
128 error = fork1(td, RFFDG | RFPROC | RFPROCDESC, 0, &p2,
131 td->td_retval[0] = p2->p_pid;
132 td->td_retval[1] = 0;
133 error = copyout(&fd, uap->fdp, sizeof(fd));
140 sys_vfork(struct thread *td, struct vfork_args *uap)
145 flags = RFFDG | RFPROC | RFPPWAIT | RFMEM;
146 error = fork1(td, flags, 0, &p2, NULL, 0);
148 td->td_retval[0] = p2->p_pid;
149 td->td_retval[1] = 0;
155 sys_rfork(struct thread *td, struct rfork_args *uap)
160 /* Don't allow kernel-only flags. */
161 if ((uap->flags & RFKERNELONLY) != 0)
164 AUDIT_ARG_FFLAGS(uap->flags);
165 error = fork1(td, uap->flags, 0, &p2, NULL, 0);
167 td->td_retval[0] = p2 ? p2->p_pid : 0;
168 td->td_retval[1] = 0;
173 int nprocs = 1; /* process 0 */
175 SYSCTL_INT(_kern, OID_AUTO, lastpid, CTLFLAG_RD, &lastpid, 0,
179 * Random component to lastpid generation. We mix in a random factor to make
180 * it a little harder to predict. We sanity check the modulus value to avoid
181 * doing it in critical paths. Don't let it be too small or we pointlessly
182 * waste randomness entropy, and don't let it be impossibly large. Using a
183 * modulus that is too big causes a LOT more process table scans and slows
184 * down fork processing as the pidchecked caching is defeated.
186 static int randompid = 0;
189 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
193 error = sysctl_wire_old_buffer(req, sizeof(int));
196 sx_xlock(&allproc_lock);
198 error = sysctl_handle_int(oidp, &pid, 0, req);
199 if (error == 0 && req->newptr != NULL) {
200 if (pid < 0 || pid > pid_max - 100) /* out of range */
202 else if (pid < 2) /* NOP */
204 else if (pid < 100) /* Make it reasonable */
208 sx_xunlock(&allproc_lock);
212 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
213 0, 0, sysctl_kern_randompid, "I", "Random PID modulus");
216 fork_findpid(int flags)
220 static int pidchecked = 0;
223 * Requires allproc_lock in order to iterate over the list
224 * of processes, and proctree_lock to access p_pgrp.
226 sx_assert(&allproc_lock, SX_LOCKED);
227 sx_assert(&proctree_lock, SX_LOCKED);
230 * Find an unused process ID. We remember a range of unused IDs
231 * ready to use (from lastpid+1 through pidchecked-1).
233 * If RFHIGHPID is set (used during system boot), do not allocate
236 trypid = lastpid + 1;
237 if (flags & RFHIGHPID) {
242 trypid += arc4random() % randompid;
246 * If the process ID prototype has wrapped around,
247 * restart somewhat above 0, as the low-numbered procs
248 * tend to include daemons that don't exit.
250 if (trypid >= pid_max) {
251 trypid = trypid % pid_max;
256 if (trypid >= pidchecked) {
259 pidchecked = PID_MAX;
261 * Scan the active and zombie procs to check whether this pid
262 * is in use. Remember the lowest pid that's greater
263 * than trypid, so we can avoid checking for a while.
265 * Avoid reuse of the process group id, session id or
266 * the reaper subtree id. Note that for process group
267 * and sessions, the amount of reserved pids is
268 * limited by process limit. For the subtree ids, the
269 * id is kept reserved only while there is a
270 * non-reaped process in the subtree, so amount of
271 * reserved pids is limited by process limit times
274 p = LIST_FIRST(&allproc);
276 for (; p != NULL; p = LIST_NEXT(p, p_list)) {
277 while (p->p_pid == trypid ||
278 p->p_reapsubtree == trypid ||
279 (p->p_pgrp != NULL &&
280 (p->p_pgrp->pg_id == trypid ||
281 (p->p_session != NULL &&
282 p->p_session->s_sid == trypid)))) {
284 if (trypid >= pidchecked)
287 if (p->p_pid > trypid && pidchecked > p->p_pid)
288 pidchecked = p->p_pid;
289 if (p->p_pgrp != NULL) {
290 if (p->p_pgrp->pg_id > trypid &&
291 pidchecked > p->p_pgrp->pg_id)
292 pidchecked = p->p_pgrp->pg_id;
293 if (p->p_session != NULL &&
294 p->p_session->s_sid > trypid &&
295 pidchecked > p->p_session->s_sid)
296 pidchecked = p->p_session->s_sid;
301 p = LIST_FIRST(&zombproc);
307 * RFHIGHPID does not mess with the lastpid counter during boot.
309 if (flags & RFHIGHPID)
318 fork_norfproc(struct thread *td, int flags)
323 KASSERT((flags & RFPROC) == 0,
324 ("fork_norfproc called with RFPROC set"));
327 if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
328 (flags & (RFCFDG | RFFDG))) {
330 if (thread_single(p1, SINGLE_BOUNDARY)) {
337 error = vm_forkproc(td, NULL, NULL, NULL, flags);
342 * Close all file descriptors.
344 if (flags & RFCFDG) {
345 struct filedesc *fdtmp;
346 fdtmp = fdinit(td->td_proc->p_fd, false);
352 * Unshare file descriptors (from parent).
358 if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
359 (flags & (RFCFDG | RFFDG))) {
361 thread_single_end(p1, SINGLE_BOUNDARY);
368 do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
369 struct vmspace *vm2, int pdflags)
371 struct proc *p1, *pptr;
374 struct filedesc_to_leader *fdtol;
375 struct sigacts *newsigacts;
377 sx_assert(&proctree_lock, SX_SLOCKED);
378 sx_assert(&allproc_lock, SX_XLOCKED);
384 * Increment the nprocs resource before blocking can occur. There
385 * are hard-limits as to the number of processes that can run.
389 trypid = fork_findpid(flags);
391 sx_sunlock(&proctree_lock);
393 p2->p_state = PRS_NEW; /* protect against others */
395 AUDIT_ARG_PID(p2->p_pid);
396 LIST_INSERT_HEAD(&allproc, p2, p_list);
398 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
403 sx_xunlock(&allproc_lock);
405 bcopy(&p1->p_startcopy, &p2->p_startcopy,
406 __rangeof(struct proc, p_startcopy, p_endcopy));
407 pargs_hold(p2->p_args);
410 bzero(&p2->p_startzero,
411 __rangeof(struct proc, p_startzero, p_endzero));
413 /* Tell the prison that we exist. */
414 prison_proc_hold(p2->p_ucred->cr_prison);
419 * Malloc things while we don't hold any locks.
421 if (flags & RFSIGSHARE)
424 newsigacts = sigacts_alloc();
429 if (flags & RFCFDG) {
430 fd = fdinit(p1->p_fd, false);
432 } else if (flags & RFFDG) {
433 fd = fdcopy(p1->p_fd);
436 fd = fdshare(p1->p_fd);
437 if (p1->p_fdtol == NULL)
438 p1->p_fdtol = filedesc_to_leader_alloc(NULL, NULL,
440 if ((flags & RFTHREAD) != 0) {
442 * Shared file descriptor table, and shared
446 FILEDESC_XLOCK(p1->p_fd);
447 fdtol->fdl_refcount++;
448 FILEDESC_XUNLOCK(p1->p_fd);
451 * Shared file descriptor table, and different
454 fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
459 * Make a proc table entry for the new process.
460 * Start by zeroing the section of proc that is zero-initialized,
461 * then copy the section that is copied directly from the parent.
467 bzero(&td2->td_startzero,
468 __rangeof(struct thread, td_startzero, td_endzero));
470 bcopy(&td->td_startcopy, &td2->td_startcopy,
471 __rangeof(struct thread, td_startcopy, td_endcopy));
473 bcopy(&p2->p_comm, &td2->td_name, sizeof(td2->td_name));
474 td2->td_sigstk = td->td_sigstk;
475 td2->td_flags = TDF_INMEM;
476 td2->td_lend_user_pri = PRI_MAX;
480 td2->td_vnet_lpush = NULL;
484 * Allow the scheduler to initialize the child.
491 * Duplicate sub-structures as needed.
492 * Increase reference counts on shared objects.
494 p2->p_flag = P_INMEM;
495 p2->p_flag2 = p1->p_flag2 & (P2_NOTRACE | P2_NOTRACE_EXEC);
496 p2->p_swtick = ticks;
497 if (p1->p_flag & P_PROFIL)
499 td2->td_ucred = crhold(p2->p_ucred);
501 if (flags & RFSIGSHARE) {
502 p2->p_sigacts = sigacts_hold(p1->p_sigacts);
504 sigacts_copy(newsigacts, p1->p_sigacts);
505 p2->p_sigacts = newsigacts;
508 if (flags & RFTSIGZMB)
509 p2->p_sigparent = RFTSIGNUM(flags);
510 else if (flags & RFLINUXTHPN)
511 p2->p_sigparent = SIGUSR1;
513 p2->p_sigparent = SIGCHLD;
515 p2->p_textvp = p1->p_textvp;
519 if (p1->p_flag2 & P2_INHERIT_PROTECTED) {
520 p2->p_flag |= P_PROTECTED;
521 p2->p_flag2 |= P2_INHERIT_PROTECTED;
525 * p_limit is copy-on-write. Bump its refcount.
529 pstats_fork(p1->p_stats, p2->p_stats);
534 /* Bump references to the text vnode (for procfs). */
539 * Set up linkage for kernel based threading.
541 if ((flags & RFTHREAD) != 0) {
542 mtx_lock(&ppeers_lock);
543 p2->p_peers = p1->p_peers;
545 p2->p_leader = p1->p_leader;
546 mtx_unlock(&ppeers_lock);
547 PROC_LOCK(p1->p_leader);
548 if ((p1->p_leader->p_flag & P_WEXIT) != 0) {
549 PROC_UNLOCK(p1->p_leader);
551 * The task leader is exiting, so process p1 is
552 * going to be killed shortly. Since p1 obviously
553 * isn't dead yet, we know that the leader is either
554 * sending SIGKILL's to all the processes in this
555 * task or is sleeping waiting for all the peers to
556 * exit. We let p1 complete the fork, but we need
557 * to go ahead and kill the new process p2 since
558 * the task leader may not get a chance to send
559 * SIGKILL to it. We leave it on the list so that
560 * the task leader will wait for this new process
564 kern_psignal(p2, SIGKILL);
567 PROC_UNLOCK(p1->p_leader);
573 sx_xlock(&proctree_lock);
574 PGRP_LOCK(p1->p_pgrp);
579 * Preserve some more flags in subprocess. P_PROFIL has already
582 p2->p_flag |= p1->p_flag & P_SUGID;
583 td2->td_pflags |= td->td_pflags & TDP_ALTSTACK;
584 SESS_LOCK(p1->p_session);
585 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
586 p2->p_flag |= P_CONTROLT;
587 SESS_UNLOCK(p1->p_session);
588 if (flags & RFPPWAIT)
589 p2->p_flag |= P_PPWAIT;
591 p2->p_pgrp = p1->p_pgrp;
592 LIST_INSERT_AFTER(p1, p2, p_pglist);
593 PGRP_UNLOCK(p1->p_pgrp);
594 LIST_INIT(&p2->p_children);
595 LIST_INIT(&p2->p_orphans);
597 callout_init_mtx(&p2->p_itcallout, &p2->p_mtx, 0);
600 * If PF_FORK is set, the child process inherits the
601 * procfs ioctl flags from its parent.
603 if (p1->p_pfsflags & PF_FORK) {
604 p2->p_stops = p1->p_stops;
605 p2->p_pfsflags = p1->p_pfsflags;
609 * This begins the section where we must prevent the parent
610 * from being swapped.
616 * Attach the new process to its parent.
618 * If RFNOWAIT is set, the newly created process becomes a child
619 * of init. This effectively disassociates the child from the
622 if ((flags & RFNOWAIT) != 0) {
626 p2->p_reaper = (p1->p_treeflag & P_TREE_REAPER) != 0 ?
631 LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
632 LIST_INIT(&p2->p_reaplist);
633 LIST_INSERT_HEAD(&p2->p_reaper->p_reaplist, p2, p_reapsibling);
634 if (p2->p_reaper == p1)
635 p2->p_reapsubtree = p2->p_pid;
636 sx_xunlock(&proctree_lock);
638 /* Inform accounting that we have forked. */
639 p2->p_acflag = AFORK;
647 * Finish creating the child process. It will return via a different
648 * execution path later. (ie: directly into user mode)
650 vm_forkproc(td, p2, td2, vm2, flags);
652 if (flags == (RFFDG | RFPROC)) {
653 PCPU_INC(cnt.v_forks);
654 PCPU_ADD(cnt.v_forkpages, p2->p_vmspace->vm_dsize +
655 p2->p_vmspace->vm_ssize);
656 } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
657 PCPU_INC(cnt.v_vforks);
658 PCPU_ADD(cnt.v_vforkpages, p2->p_vmspace->vm_dsize +
659 p2->p_vmspace->vm_ssize);
660 } else if (p1 == &proc0) {
661 PCPU_INC(cnt.v_kthreads);
662 PCPU_ADD(cnt.v_kthreadpages, p2->p_vmspace->vm_dsize +
663 p2->p_vmspace->vm_ssize);
665 PCPU_INC(cnt.v_rforks);
666 PCPU_ADD(cnt.v_rforkpages, p2->p_vmspace->vm_dsize +
667 p2->p_vmspace->vm_ssize);
671 * Associate the process descriptor with the process before anything
672 * can happen that might cause that process to need the descriptor.
673 * However, don't do this until after fork(2) can no longer fail.
675 if (flags & RFPROCDESC)
676 procdesc_new(p2, pdflags);
679 * Both processes are set up, now check if any loadable modules want
680 * to adjust anything.
682 EVENTHANDLER_INVOKE(process_fork, p1, p2, flags);
685 * Set the child start time and mark the process as being complete.
689 microuptime(&p2->p_stats->p_start);
691 p2->p_state = PRS_NORMAL;
696 * Tell the DTrace fasttrap provider about the new process so that any
697 * tracepoints inherited from the parent can be removed. We have to do
698 * this only after p_state is PRS_NORMAL since the fasttrap module will
699 * use pfind() later on.
701 if ((flags & RFMEM) == 0 && dtrace_fasttrap_fork)
702 dtrace_fasttrap_fork(p1, p2);
704 if ((p1->p_flag & (P_TRACED | P_FOLLOWFORK)) == (P_TRACED |
707 * Arrange for debugger to receive the fork event.
709 * We can report PL_FLAG_FORKED regardless of
710 * P_FOLLOWFORK settings, but it does not make a sense
713 td->td_dbgflags |= TDB_FORK;
714 td->td_dbg_forked = p2->p_pid;
715 td2->td_dbgflags |= TDB_STOPATFORK;
719 if (flags & RFPPWAIT) {
720 td->td_pflags |= TDP_RFPPWAIT;
721 td->td_rfppwait_p = p2;
724 if ((flags & RFSTOPPED) == 0) {
726 * If RFSTOPPED not requested, make child runnable and
731 sched_add(td2, SRQ_BORING);
736 * Now can be swapped.
742 * Tell any interested parties about the new process.
744 knote_fork(&p1->p_klist, p2->p_pid);
745 SDT_PROBE(proc, kernel, , create, p2, p1, flags, 0, 0);
748 * Wait until debugger is attached to child.
751 while ((td2->td_dbgflags & TDB_STOPATFORK) != 0)
752 cv_wait(&p2->p_dbgwait, &p2->p_mtx);
759 fork1(struct thread *td, int flags, int pages, struct proc **procp,
760 int *procdescp, int pdflags)
763 struct proc *newproc;
767 vm_ooffset_t mem_charged;
770 static struct timeval lastfail;
771 struct file *fp_procdesc = NULL;
773 /* Check for the undefined or unimplemented flags. */
774 if ((flags & ~(RFFLAGS | RFTSIGFLAGS(RFTSIGMASK))) != 0)
777 /* Signal value requires RFTSIGZMB. */
778 if ((flags & RFTSIGFLAGS(RFTSIGMASK)) != 0 && (flags & RFTSIGZMB) == 0)
781 /* Can't copy and clear. */
782 if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
785 /* Check the validity of the signal number. */
786 if ((flags & RFTSIGZMB) != 0 && (u_int)RFTSIGNUM(flags) > _SIG_MAXSIG)
789 if ((flags & RFPROCDESC) != 0) {
790 /* Can't not create a process yet get a process descriptor. */
791 if ((flags & RFPROC) == 0)
794 /* Must provide a place to put a procdesc if creating one. */
795 if (procdescp == NULL)
802 * Here we don't create a new process, but we divorce
803 * certain parts of a process from itself.
805 if ((flags & RFPROC) == 0) {
807 return (fork_norfproc(td, flags));
811 * If required, create a process descriptor in the parent first; we
812 * will abandon it if something goes wrong. We don't finit() until
815 if (flags & RFPROCDESC) {
816 error = falloc(td, &fp_procdesc, procdescp, 0);
824 pages = KSTACK_PAGES;
825 /* Allocate new proc. */
826 newproc = uma_zalloc(proc_zone, M_WAITOK);
827 td2 = FIRST_THREAD_IN_PROC(newproc);
829 td2 = thread_alloc(pages);
834 proc_linkup(newproc, td2);
836 if (td2->td_kstack == 0 || td2->td_kstack_pages != pages) {
837 if (td2->td_kstack != 0)
838 vm_thread_dispose(td2);
839 if (!thread_alloc_stack(td2, pages)) {
846 if ((flags & RFMEM) == 0) {
847 vm2 = vmspace_fork(p1->p_vmspace, &mem_charged);
852 if (!swap_reserve(mem_charged)) {
854 * The swap reservation failed. The accounting
855 * from the entries of the copied vm2 will be
856 * substracted in vmspace_free(), so force the
859 swap_reserve_force(mem_charged);
867 * XXX: This is ugly; when we copy resource usage, we need to bump
868 * per-cred resource counters.
870 proc_set_cred_init(newproc, crhold(td->td_ucred));
873 * Initialize resource accounting for the child process.
875 error = racct_proc_fork(p1, newproc);
882 mac_proc_init(newproc);
884 knlist_init_mtx(&newproc->p_klist, &newproc->p_mtx);
885 STAILQ_INIT(&newproc->p_ktr);
887 /* We have to lock the process tree while we look for a pid. */
888 sx_slock(&proctree_lock);
891 * Although process entries are dynamically created, we still keep
892 * a global limit on the maximum number we will create. Don't allow
893 * a nonprivileged user to use the last ten processes; don't let root
894 * exceed the limit. The variable nprocs is the current number of
895 * processes, maxproc is the limit.
897 sx_xlock(&allproc_lock);
898 if ((nprocs >= maxproc - 10 && priv_check_cred(td->td_ucred,
899 PRIV_MAXPROC, 0) != 0) || nprocs >= maxproc) {
905 * Increment the count of procs running with this uid. Don't allow
906 * a nonprivileged user to exceed their current limit.
908 * XXXRW: Can we avoid privilege here if it's not needed?
910 error = priv_check_cred(td->td_ucred, PRIV_PROC_LIMIT, 0);
912 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1, 0);
915 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1,
916 lim_cur(p1, RLIMIT_NPROC));
920 do_fork(td, flags, newproc, td2, vm2, pdflags);
923 * Return child proc pointer to parent.
926 if (flags & RFPROCDESC) {
927 procdesc_finit(newproc->p_procdesc, fp_procdesc);
928 fdrop(fp_procdesc, td);
930 racct_proc_fork_done(newproc);
936 sx_sunlock(&proctree_lock);
937 if (ppsratecheck(&lastfail, &curfail, 1))
938 printf("maxproc limit exceeded by uid %u (pid %d); see tuning(7) and login.conf(5)\n",
939 td->td_ucred->cr_ruid, p1->p_pid);
940 sx_xunlock(&allproc_lock);
942 mac_proc_destroy(newproc);
944 racct_proc_exit(newproc);
946 crfree(proc_set_cred(newproc, NULL));
950 uma_zfree(proc_zone, newproc);
951 if ((flags & RFPROCDESC) != 0 && fp_procdesc != NULL) {
952 fdclose(td, fp_procdesc, *procdescp);
953 fdrop(fp_procdesc, td);
955 pause("fork", hz / 2);
960 * Handle the return of a child process from fork1(). This function
961 * is called from the MD fork_trampoline() entry point.
964 fork_exit(void (*callout)(void *, struct trapframe *), void *arg,
965 struct trapframe *frame)
973 KASSERT(p->p_state == PRS_NORMAL, ("executing process is still new"));
975 CTR4(KTR_PROC, "fork_exit: new thread %p (td_sched %p, pid %d, %s)",
976 td, td->td_sched, p->p_pid, td->td_name);
980 * Processes normally resume in mi_switch() after being
981 * cpu_switch()'ed to, but when children start up they arrive here
982 * instead, so we must do much the same things as mi_switch() would.
984 if ((dtd = PCPU_GET(deadthread))) {
985 PCPU_SET(deadthread, NULL);
991 * cpu_set_fork_handler intercepts this function call to
992 * have this call a non-return function to stay in kernel mode.
993 * initproc has its own fork handler, but it does return.
995 KASSERT(callout != NULL, ("NULL callout in fork_exit"));
999 * Check if a kernel thread misbehaved and returned from its main
1002 if (p->p_flag & P_KTHREAD) {
1003 printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
1004 td->td_name, p->p_pid);
1007 mtx_assert(&Giant, MA_NOTOWNED);
1009 if (p->p_sysent->sv_schedtail != NULL)
1010 (p->p_sysent->sv_schedtail)(td);
1014 * Simplified back end of syscall(), used when returning from fork()
1015 * directly into user mode. Giant is not held on entry, and must not
1016 * be held on return. This function is passed in to fork_exit() as the
1017 * first parameter and is called when returning to a new userland process.
1020 fork_return(struct thread *td, struct trapframe *frame)
1022 struct proc *p, *dbg;
1024 if (td->td_dbgflags & TDB_STOPATFORK) {
1026 sx_xlock(&proctree_lock);
1028 if ((p->p_pptr->p_flag & (P_TRACED | P_FOLLOWFORK)) ==
1029 (P_TRACED | P_FOLLOWFORK)) {
1031 * If debugger still wants auto-attach for the
1032 * parent's children, do it now.
1034 dbg = p->p_pptr->p_pptr;
1035 p->p_flag |= P_TRACED;
1036 p->p_oppid = p->p_pptr->p_pid;
1037 proc_reparent(p, dbg);
1038 sx_xunlock(&proctree_lock);
1039 td->td_dbgflags |= TDB_CHILD;
1040 ptracestop(td, SIGSTOP);
1041 td->td_dbgflags &= ~TDB_CHILD;
1044 * ... otherwise clear the request.
1046 sx_xunlock(&proctree_lock);
1047 td->td_dbgflags &= ~TDB_STOPATFORK;
1048 cv_broadcast(&p->p_dbgwait);
1056 if (KTRPOINT(td, KTR_SYSRET))
1057 ktrsysret(SYS_fork, 0, 0);