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
20 * without specific prior written permission.
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
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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
34 * @(#)kern_fork.c 8.6 (Berkeley) 4/8/94
37 #include <sys/cdefs.h>
38 __FBSDID("$FreeBSD$");
40 #include "opt_kdtrace.h"
41 #include "opt_ktrace.h"
42 #include "opt_kstack_pages.h"
43 #include "opt_procdesc.h"
45 #include <sys/param.h>
46 #include <sys/systm.h>
47 #include <sys/sysproto.h>
48 #include <sys/eventhandler.h>
49 #include <sys/fcntl.h>
50 #include <sys/filedesc.h>
52 #include <sys/kernel.h>
53 #include <sys/kthread.h>
54 #include <sys/sysctl.h>
56 #include <sys/malloc.h>
57 #include <sys/mutex.h>
60 #include <sys/procdesc.h>
61 #include <sys/pioctl.h>
62 #include <sys/ptrace.h>
63 #include <sys/racct.h>
64 #include <sys/resourcevar.h>
65 #include <sys/sched.h>
66 #include <sys/syscall.h>
67 #include <sys/vmmeter.h>
68 #include <sys/vnode.h>
71 #include <sys/ktrace.h>
72 #include <sys/unistd.h>
75 #include <sys/sysent.h>
76 #include <sys/signalvar.h>
78 #include <security/audit/audit.h>
79 #include <security/mac/mac_framework.h>
83 #include <vm/vm_map.h>
84 #include <vm/vm_extern.h>
88 #include <sys/dtrace_bsd.h>
89 dtrace_fork_func_t dtrace_fasttrap_fork;
92 SDT_PROVIDER_DECLARE(proc);
93 SDT_PROBE_DEFINE3(proc, kernel, , create, "struct proc *",
94 "struct proc *", "int");
96 #ifndef _SYS_SYSPROTO_H_
104 sys_fork(struct thread *td, struct fork_args *uap)
109 error = fork1(td, RFFDG | RFPROC, 0, &p2, NULL, 0);
111 td->td_retval[0] = p2->p_pid;
112 td->td_retval[1] = 0;
121 struct pdfork_args *uap;
128 * It is necessary to return fd by reference because 0 is a valid file
129 * descriptor number, and the child needs to be able to distinguish
130 * itself from the parent using the return value.
132 error = fork1(td, RFFDG | RFPROC | RFPROCDESC, 0, &p2,
135 td->td_retval[0] = p2->p_pid;
136 td->td_retval[1] = 0;
137 error = copyout(&fd, uap->fdp, sizeof(fd));
147 sys_vfork(struct thread *td, struct vfork_args *uap)
152 flags = RFFDG | RFPROC | RFPPWAIT | RFMEM;
153 error = fork1(td, flags, 0, &p2, NULL, 0);
155 td->td_retval[0] = p2->p_pid;
156 td->td_retval[1] = 0;
162 sys_rfork(struct thread *td, struct rfork_args *uap)
167 /* Don't allow kernel-only flags. */
168 if ((uap->flags & RFKERNELONLY) != 0)
171 AUDIT_ARG_FFLAGS(uap->flags);
172 error = fork1(td, uap->flags, 0, &p2, NULL, 0);
174 td->td_retval[0] = p2 ? p2->p_pid : 0;
175 td->td_retval[1] = 0;
180 int nprocs = 1; /* process 0 */
182 SYSCTL_INT(_kern, OID_AUTO, lastpid, CTLFLAG_RD, &lastpid, 0,
186 * Random component to lastpid generation. We mix in a random factor to make
187 * it a little harder to predict. We sanity check the modulus value to avoid
188 * doing it in critical paths. Don't let it be too small or we pointlessly
189 * waste randomness entropy, and don't let it be impossibly large. Using a
190 * modulus that is too big causes a LOT more process table scans and slows
191 * down fork processing as the pidchecked caching is defeated.
193 static int randompid = 0;
196 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
200 error = sysctl_wire_old_buffer(req, sizeof(int));
203 sx_xlock(&allproc_lock);
205 error = sysctl_handle_int(oidp, &pid, 0, req);
206 if (error == 0 && req->newptr != NULL) {
207 if (pid < 0 || pid > pid_max - 100) /* out of range */
209 else if (pid < 2) /* NOP */
211 else if (pid < 100) /* Make it reasonable */
215 sx_xunlock(&allproc_lock);
219 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
220 0, 0, sysctl_kern_randompid, "I", "Random PID modulus");
223 fork_findpid(int flags)
227 static int pidchecked = 0;
230 * Requires allproc_lock in order to iterate over the list
231 * of processes, and proctree_lock to access p_pgrp.
233 sx_assert(&allproc_lock, SX_LOCKED);
234 sx_assert(&proctree_lock, SX_LOCKED);
237 * Find an unused process ID. We remember a range of unused IDs
238 * ready to use (from lastpid+1 through pidchecked-1).
240 * If RFHIGHPID is set (used during system boot), do not allocate
243 trypid = lastpid + 1;
244 if (flags & RFHIGHPID) {
249 trypid += arc4random() % randompid;
253 * If the process ID prototype has wrapped around,
254 * restart somewhat above 0, as the low-numbered procs
255 * tend to include daemons that don't exit.
257 if (trypid >= pid_max) {
258 trypid = trypid % pid_max;
263 if (trypid >= pidchecked) {
266 pidchecked = PID_MAX;
268 * Scan the active and zombie procs to check whether this pid
269 * is in use. Remember the lowest pid that's greater
270 * than trypid, so we can avoid checking for a while.
272 * Avoid reuse of the process group id, session id or
273 * the reaper subtree id. Note that for process group
274 * and sessions, the amount of reserved pids is
275 * limited by process limit. For the subtree ids, the
276 * id is kept reserved only while there is a
277 * non-reaped process in the subtree, so amount of
278 * reserved pids is limited by process limit times
281 p = LIST_FIRST(&allproc);
283 for (; p != NULL; p = LIST_NEXT(p, p_list)) {
284 while (p->p_pid == trypid ||
285 p->p_reapsubtree == trypid ||
286 (p->p_pgrp != NULL &&
287 (p->p_pgrp->pg_id == trypid ||
288 (p->p_session != NULL &&
289 p->p_session->s_sid == trypid)))) {
291 if (trypid >= pidchecked)
294 if (p->p_pid > trypid && pidchecked > p->p_pid)
295 pidchecked = p->p_pid;
296 if (p->p_pgrp != NULL) {
297 if (p->p_pgrp->pg_id > trypid &&
298 pidchecked > p->p_pgrp->pg_id)
299 pidchecked = p->p_pgrp->pg_id;
300 if (p->p_session != NULL &&
301 p->p_session->s_sid > trypid &&
302 pidchecked > p->p_session->s_sid)
303 pidchecked = p->p_session->s_sid;
308 p = LIST_FIRST(&zombproc);
314 * RFHIGHPID does not mess with the lastpid counter during boot.
316 if (flags & RFHIGHPID)
325 fork_norfproc(struct thread *td, int flags)
330 KASSERT((flags & RFPROC) == 0,
331 ("fork_norfproc called with RFPROC set"));
334 if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
335 (flags & (RFCFDG | RFFDG))) {
337 if (thread_single(p1, SINGLE_BOUNDARY)) {
344 error = vm_forkproc(td, NULL, NULL, NULL, flags);
349 * Close all file descriptors.
351 if (flags & RFCFDG) {
352 struct filedesc *fdtmp;
353 fdtmp = fdinit(td->td_proc->p_fd);
359 * Unshare file descriptors (from parent).
365 if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
366 (flags & (RFCFDG | RFFDG))) {
368 thread_single_end(p1, SINGLE_BOUNDARY);
375 do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
376 struct vmspace *vm2, int pdflags)
378 struct proc *p1, *pptr;
381 struct filedesc_to_leader *fdtol;
382 struct sigacts *newsigacts;
384 sx_assert(&proctree_lock, SX_SLOCKED);
385 sx_assert(&allproc_lock, SX_XLOCKED);
390 trypid = fork_findpid(flags);
392 sx_sunlock(&proctree_lock);
394 p2->p_state = PRS_NEW; /* protect against others */
396 AUDIT_ARG_PID(p2->p_pid);
397 LIST_INSERT_HEAD(&allproc, p2, p_list);
399 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
404 sx_xunlock(&allproc_lock);
406 bcopy(&p1->p_startcopy, &p2->p_startcopy,
407 __rangeof(struct proc, p_startcopy, p_endcopy));
408 pargs_hold(p2->p_args);
411 bzero(&p2->p_startzero,
412 __rangeof(struct proc, p_startzero, p_endzero));
415 p2->p_ucred = crhold(td->td_ucred);
417 /* Tell the prison that we exist. */
418 prison_proc_hold(p2->p_ucred->cr_prison);
423 * Malloc things while we don't hold any locks.
425 if (flags & RFSIGSHARE)
428 newsigacts = sigacts_alloc();
433 if (flags & RFCFDG) {
434 fd = fdinit(p1->p_fd);
436 } else if (flags & RFFDG) {
437 fd = fdcopy(p1->p_fd);
440 fd = fdshare(p1->p_fd);
441 if (p1->p_fdtol == NULL)
442 p1->p_fdtol = filedesc_to_leader_alloc(NULL, NULL,
444 if ((flags & RFTHREAD) != 0) {
446 * Shared file descriptor table, and shared
450 FILEDESC_XLOCK(p1->p_fd);
451 fdtol->fdl_refcount++;
452 FILEDESC_XUNLOCK(p1->p_fd);
455 * Shared file descriptor table, and different
458 fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
463 * Make a proc table entry for the new process.
464 * Start by zeroing the section of proc that is zero-initialized,
465 * then copy the section that is copied directly from the parent.
471 bzero(&td2->td_startzero,
472 __rangeof(struct thread, td_startzero, td_endzero));
475 bcopy(&td->td_startcopy, &td2->td_startcopy,
476 __rangeof(struct thread, td_startcopy, td_endcopy));
478 bcopy(&p2->p_comm, &td2->td_name, sizeof(td2->td_name));
479 td2->td_sigstk = td->td_sigstk;
480 td2->td_flags = TDF_INMEM;
481 td2->td_lend_user_pri = PRI_MAX;
482 td2->td_dbg_sc_code = td->td_dbg_sc_code;
483 td2->td_dbg_sc_narg = td->td_dbg_sc_narg;
487 td2->td_vnet_lpush = NULL;
491 * Allow the scheduler to initialize the child.
498 * Duplicate sub-structures as needed.
499 * Increase reference counts on shared objects.
501 p2->p_flag = P_INMEM;
502 p2->p_flag2 = p1->p_flag2 & (P2_NOTRACE | P2_NOTRACE_EXEC);
503 p2->p_swtick = ticks;
504 if (p1->p_flag & P_PROFIL)
506 td2->td_ucred = crhold(p2->p_ucred);
508 if (flags & RFSIGSHARE) {
509 p2->p_sigacts = sigacts_hold(p1->p_sigacts);
511 sigacts_copy(newsigacts, p1->p_sigacts);
512 p2->p_sigacts = newsigacts;
515 if (flags & RFTSIGZMB)
516 p2->p_sigparent = RFTSIGNUM(flags);
517 else if (flags & RFLINUXTHPN)
518 p2->p_sigparent = SIGUSR1;
520 p2->p_sigparent = SIGCHLD;
522 p2->p_textvp = p1->p_textvp;
526 if (p1->p_flag2 & P2_INHERIT_PROTECTED) {
527 p2->p_flag |= P_PROTECTED;
528 p2->p_flag2 |= P2_INHERIT_PROTECTED;
532 * p_limit is copy-on-write. Bump its refcount.
536 pstats_fork(p1->p_stats, p2->p_stats);
541 /* Bump references to the text vnode (for procfs). */
546 * Set up linkage for kernel based threading.
548 if ((flags & RFTHREAD) != 0) {
549 mtx_lock(&ppeers_lock);
550 p2->p_peers = p1->p_peers;
552 p2->p_leader = p1->p_leader;
553 mtx_unlock(&ppeers_lock);
554 PROC_LOCK(p1->p_leader);
555 if ((p1->p_leader->p_flag & P_WEXIT) != 0) {
556 PROC_UNLOCK(p1->p_leader);
558 * The task leader is exiting, so process p1 is
559 * going to be killed shortly. Since p1 obviously
560 * isn't dead yet, we know that the leader is either
561 * sending SIGKILL's to all the processes in this
562 * task or is sleeping waiting for all the peers to
563 * exit. We let p1 complete the fork, but we need
564 * to go ahead and kill the new process p2 since
565 * the task leader may not get a chance to send
566 * SIGKILL to it. We leave it on the list so that
567 * the task leader will wait for this new process
571 kern_psignal(p2, SIGKILL);
574 PROC_UNLOCK(p1->p_leader);
580 sx_xlock(&proctree_lock);
581 PGRP_LOCK(p1->p_pgrp);
586 * Preserve some more flags in subprocess. P_PROFIL has already
589 p2->p_flag |= p1->p_flag & P_SUGID;
590 td2->td_pflags |= td->td_pflags & TDP_ALTSTACK;
591 SESS_LOCK(p1->p_session);
592 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
593 p2->p_flag |= P_CONTROLT;
594 SESS_UNLOCK(p1->p_session);
595 if (flags & RFPPWAIT)
596 p2->p_flag |= P_PPWAIT;
598 p2->p_pgrp = p1->p_pgrp;
599 LIST_INSERT_AFTER(p1, p2, p_pglist);
600 PGRP_UNLOCK(p1->p_pgrp);
601 LIST_INIT(&p2->p_children);
602 LIST_INIT(&p2->p_orphans);
604 callout_init_mtx(&p2->p_itcallout, &p2->p_mtx, 0);
607 * If PF_FORK is set, the child process inherits the
608 * procfs ioctl flags from its parent.
610 if (p1->p_pfsflags & PF_FORK) {
611 p2->p_stops = p1->p_stops;
612 p2->p_pfsflags = p1->p_pfsflags;
616 * This begins the section where we must prevent the parent
617 * from being swapped.
623 * Attach the new process to its parent.
625 * If RFNOWAIT is set, the newly created process becomes a child
626 * of init. This effectively disassociates the child from the
629 if ((flags & RFNOWAIT) != 0) {
633 p2->p_reaper = (p1->p_treeflag & P_TREE_REAPER) != 0 ?
638 LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
639 LIST_INIT(&p2->p_reaplist);
640 LIST_INSERT_HEAD(&p2->p_reaper->p_reaplist, p2, p_reapsibling);
641 if (p2->p_reaper == p1)
642 p2->p_reapsubtree = p2->p_pid;
644 p2->p_reapsubtree = p1->p_reapsubtree;
645 sx_xunlock(&proctree_lock);
647 /* Inform accounting that we have forked. */
648 p2->p_acflag = AFORK;
656 * Finish creating the child process. It will return via a different
657 * execution path later. (ie: directly into user mode)
659 vm_forkproc(td, p2, td2, vm2, flags);
661 if (flags == (RFFDG | RFPROC)) {
662 PCPU_INC(cnt.v_forks);
663 PCPU_ADD(cnt.v_forkpages, p2->p_vmspace->vm_dsize +
664 p2->p_vmspace->vm_ssize);
665 } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
666 PCPU_INC(cnt.v_vforks);
667 PCPU_ADD(cnt.v_vforkpages, p2->p_vmspace->vm_dsize +
668 p2->p_vmspace->vm_ssize);
669 } else if (p1 == &proc0) {
670 PCPU_INC(cnt.v_kthreads);
671 PCPU_ADD(cnt.v_kthreadpages, p2->p_vmspace->vm_dsize +
672 p2->p_vmspace->vm_ssize);
674 PCPU_INC(cnt.v_rforks);
675 PCPU_ADD(cnt.v_rforkpages, p2->p_vmspace->vm_dsize +
676 p2->p_vmspace->vm_ssize);
681 * Associate the process descriptor with the process before anything
682 * can happen that might cause that process to need the descriptor.
683 * However, don't do this until after fork(2) can no longer fail.
685 if (flags & RFPROCDESC)
686 procdesc_new(p2, pdflags);
690 * Both processes are set up, now check if any loadable modules want
691 * to adjust anything.
693 EVENTHANDLER_INVOKE(process_fork, p1, p2, flags);
696 * Set the child start time and mark the process as being complete.
700 microuptime(&p2->p_stats->p_start);
702 p2->p_state = PRS_NORMAL;
707 * Tell the DTrace fasttrap provider about the new process so that any
708 * tracepoints inherited from the parent can be removed. We have to do
709 * this only after p_state is PRS_NORMAL since the fasttrap module will
710 * use pfind() later on.
712 if ((flags & RFMEM) == 0 && dtrace_fasttrap_fork)
713 dtrace_fasttrap_fork(p1, p2);
715 if ((p1->p_flag & (P_TRACED | P_FOLLOWFORK)) == (P_TRACED |
718 * Arrange for debugger to receive the fork event.
720 * We can report PL_FLAG_FORKED regardless of
721 * P_FOLLOWFORK settings, but it does not make a sense
724 td->td_dbgflags |= TDB_FORK;
725 td->td_dbg_forked = p2->p_pid;
726 td2->td_dbgflags |= TDB_STOPATFORK;
730 if (flags & RFPPWAIT) {
731 td->td_pflags |= TDP_RFPPWAIT;
732 td->td_rfppwait_p = p2;
735 if ((flags & RFSTOPPED) == 0) {
737 * If RFSTOPPED not requested, make child runnable and
742 sched_add(td2, SRQ_BORING);
747 * Now can be swapped.
753 * Tell any interested parties about the new process.
755 knote_fork(&p1->p_klist, p2->p_pid);
756 SDT_PROBE3(proc, kernel, , create, p2, p1, flags);
759 * Wait until debugger is attached to child.
762 while ((td2->td_dbgflags & TDB_STOPATFORK) != 0)
763 cv_wait(&p2->p_dbgwait, &p2->p_mtx);
770 fork1(struct thread *td, int flags, int pages, struct proc **procp,
771 int *procdescp, int pdflags)
773 struct proc *p1, *newproc;
777 struct file *fp_procdesc;
779 vm_ooffset_t mem_charged;
780 int error, nprocs_new, ok;
782 static struct timeval lastfail;
784 /* Check for the undefined or unimplemented flags. */
785 if ((flags & ~(RFFLAGS | RFTSIGFLAGS(RFTSIGMASK))) != 0)
788 /* Signal value requires RFTSIGZMB. */
789 if ((flags & RFTSIGFLAGS(RFTSIGMASK)) != 0 && (flags & RFTSIGZMB) == 0)
792 /* Can't copy and clear. */
793 if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
796 /* Check the validity of the signal number. */
797 if ((flags & RFTSIGZMB) != 0 && (u_int)RFTSIGNUM(flags) > _SIG_MAXSIG)
801 if ((flags & RFPROCDESC) != 0) {
802 /* Can't not create a process yet get a process descriptor. */
803 if ((flags & RFPROC) == 0)
806 /* Must provide a place to put a procdesc if creating one. */
807 if (procdescp == NULL)
815 * Here we don't create a new process, but we divorce
816 * certain parts of a process from itself.
818 if ((flags & RFPROC) == 0) {
820 return (fork_norfproc(td, flags));
830 * Increment the nprocs resource before allocations occur.
831 * Although process entries are dynamically created, we still
832 * keep a global limit on the maximum number we will
833 * create. There are hard-limits as to the number of processes
834 * that can run, established by the KVA and memory usage for
837 * Don't allow a nonprivileged user to use the last ten
838 * processes; don't let root exceed the limit.
840 nprocs_new = atomic_fetchadd_int(&nprocs, 1) + 1;
841 if ((nprocs_new >= maxproc - 10 && priv_check_cred(td->td_ucred,
842 PRIV_MAXPROC, 0) != 0) || nprocs_new >= maxproc) {
843 sx_xlock(&allproc_lock);
844 if (ppsratecheck(&lastfail, &curfail, 1)) {
845 printf("maxproc limit exceeded by uid %u (pid %d); "
846 "see tuning(7) and login.conf(5)\n",
847 td->td_ucred->cr_ruid, p1->p_pid);
849 sx_xunlock(&allproc_lock);
856 * If required, create a process descriptor in the parent first; we
857 * will abandon it if something goes wrong. We don't finit() until
860 if (flags & RFPROCDESC) {
861 error = falloc(td, &fp_procdesc, procdescp, 0);
869 pages = KSTACK_PAGES;
870 /* Allocate new proc. */
871 newproc = uma_zalloc(proc_zone, M_WAITOK);
872 td2 = FIRST_THREAD_IN_PROC(newproc);
874 td2 = thread_alloc(pages);
879 proc_linkup(newproc, td2);
881 if (td2->td_kstack == 0 || td2->td_kstack_pages != pages) {
882 if (td2->td_kstack != 0)
883 vm_thread_dispose(td2);
884 if (!thread_alloc_stack(td2, pages)) {
891 if ((flags & RFMEM) == 0) {
892 vm2 = vmspace_fork(p1->p_vmspace, &mem_charged);
897 if (!swap_reserve(mem_charged)) {
899 * The swap reservation failed. The accounting
900 * from the entries of the copied vm2 will be
901 * substracted in vmspace_free(), so force the
904 swap_reserve_force(mem_charged);
912 * XXX: This is ugly; when we copy resource usage, we need to bump
913 * per-cred resource counters.
915 newproc->p_ucred = p1->p_ucred;
918 * Initialize resource accounting for the child process.
920 error = racct_proc_fork(p1, newproc);
927 mac_proc_init(newproc);
929 knlist_init_mtx(&newproc->p_klist, &newproc->p_mtx);
930 STAILQ_INIT(&newproc->p_ktr);
932 /* We have to lock the process tree while we look for a pid. */
933 sx_slock(&proctree_lock);
934 sx_xlock(&allproc_lock);
937 * Increment the count of procs running with this uid. Don't allow
938 * a nonprivileged user to exceed their current limit.
940 * XXXRW: Can we avoid privilege here if it's not needed?
942 error = priv_check_cred(td->td_ucred, PRIV_PROC_LIMIT, 0);
944 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1, 0);
947 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1,
948 lim_cur(p1, RLIMIT_NPROC));
952 do_fork(td, flags, newproc, td2, vm2, pdflags);
955 * Return child proc pointer to parent.
959 if (flags & RFPROCDESC) {
960 procdesc_finit(newproc->p_procdesc, fp_procdesc);
961 fdrop(fp_procdesc, td);
964 racct_proc_fork_done(newproc);
969 sx_sunlock(&proctree_lock);
970 sx_xunlock(&allproc_lock);
972 mac_proc_destroy(newproc);
974 racct_proc_exit(newproc);
978 uma_zfree(proc_zone, newproc);
980 if ((flags & RFPROCDESC) != 0 && fp_procdesc != NULL) {
981 fdclose(td->td_proc->p_fd, fp_procdesc, *procdescp, td);
982 fdrop(fp_procdesc, td);
985 atomic_add_int(&nprocs, -1);
986 pause("fork", hz / 2);
991 * Handle the return of a child process from fork1(). This function
992 * is called from the MD fork_trampoline() entry point.
995 fork_exit(void (*callout)(void *, struct trapframe *), void *arg,
996 struct trapframe *frame)
1004 KASSERT(p->p_state == PRS_NORMAL, ("executing process is still new"));
1006 CTR4(KTR_PROC, "fork_exit: new thread %p (td_sched %p, pid %d, %s)",
1007 td, td->td_sched, p->p_pid, td->td_name);
1009 sched_fork_exit(td);
1011 * Processes normally resume in mi_switch() after being
1012 * cpu_switch()'ed to, but when children start up they arrive here
1013 * instead, so we must do much the same things as mi_switch() would.
1015 if ((dtd = PCPU_GET(deadthread))) {
1016 PCPU_SET(deadthread, NULL);
1022 * cpu_set_fork_handler intercepts this function call to
1023 * have this call a non-return function to stay in kernel mode.
1024 * initproc has its own fork handler, but it does return.
1026 KASSERT(callout != NULL, ("NULL callout in fork_exit"));
1027 callout(arg, frame);
1030 * Check if a kernel thread misbehaved and returned from its main
1033 if (p->p_flag & P_KTHREAD) {
1034 printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
1035 td->td_name, p->p_pid);
1038 mtx_assert(&Giant, MA_NOTOWNED);
1040 if (p->p_sysent->sv_schedtail != NULL)
1041 (p->p_sysent->sv_schedtail)(td);
1045 * Simplified back end of syscall(), used when returning from fork()
1046 * directly into user mode. Giant is not held on entry, and must not
1047 * be held on return. This function is passed in to fork_exit() as the
1048 * first parameter and is called when returning to a new userland process.
1051 fork_return(struct thread *td, struct trapframe *frame)
1053 struct proc *p, *dbg;
1056 if (td->td_dbgflags & TDB_STOPATFORK) {
1057 sx_xlock(&proctree_lock);
1059 if ((p->p_pptr->p_flag & (P_TRACED | P_FOLLOWFORK)) ==
1060 (P_TRACED | P_FOLLOWFORK)) {
1062 * If debugger still wants auto-attach for the
1063 * parent's children, do it now.
1065 dbg = p->p_pptr->p_pptr;
1066 p->p_flag |= P_TRACED;
1067 p->p_oppid = p->p_pptr->p_pid;
1069 "fork_return: attaching to new child pid %d: oppid %d",
1070 p->p_pid, p->p_oppid);
1071 proc_reparent(p, dbg);
1072 sx_xunlock(&proctree_lock);
1073 td->td_dbgflags |= TDB_CHILD | TDB_SCX;
1074 ptracestop(td, SIGSTOP);
1075 td->td_dbgflags &= ~(TDB_CHILD | TDB_SCX);
1078 * ... otherwise clear the request.
1080 sx_xunlock(&proctree_lock);
1081 td->td_dbgflags &= ~TDB_STOPATFORK;
1082 cv_broadcast(&p->p_dbgwait);
1085 } else if (p->p_flag & P_TRACED) {
1087 * This is the start of a new thread in a traced
1088 * process. Report a system call exit event.
1091 td->td_dbgflags |= TDB_SCX;
1092 _STOPEVENT(p, S_SCX, td->td_dbg_sc_code);
1093 if ((p->p_stops & S_PT_SCX) != 0)
1094 ptracestop(td, SIGTRAP);
1095 td->td_dbgflags &= ~TDB_SCX;
1102 if (KTRPOINT(td, KTR_SYSRET))
1103 ktrsysret(SYS_fork, 0, 0);