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
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34 * @(#)kern_fork.c 8.6 (Berkeley) 4/8/94
37 #include <sys/cdefs.h>
38 __FBSDID("$FreeBSD$");
40 #include "opt_ktrace.h"
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>
52 #include <sys/malloc.h>
53 #include <sys/mutex.h>
56 #include <sys/pioctl.h>
57 #include <sys/resourcevar.h>
58 #include <sys/sched.h>
59 #include <sys/syscall.h>
60 #include <sys/vmmeter.h>
61 #include <sys/vnode.h>
64 #include <sys/ktrace.h>
65 #include <sys/unistd.h>
67 #include <sys/signalvar.h>
69 #include <security/audit/audit.h>
70 #include <security/mac/mac_framework.h>
74 #include <vm/vm_map.h>
75 #include <vm/vm_extern.h>
79 #ifndef _SYS_SYSPROTO_H_
89 struct fork_args *uap;
94 error = fork1(td, RFFDG | RFPROC, 0, &p2);
96 td->td_retval[0] = p2->p_pid;
106 struct vfork_args *uap;
111 error = fork1(td, RFFDG | RFPROC | RFPPWAIT | RFMEM, 0, &p2);
113 td->td_retval[0] = p2->p_pid;
114 td->td_retval[1] = 0;
122 struct rfork_args *uap;
127 /* Don't allow kernel-only flags. */
128 if ((uap->flags & RFKERNELONLY) != 0)
131 AUDIT_ARG(fflags, uap->flags);
132 error = fork1(td, uap->flags, 0, &p2);
134 td->td_retval[0] = p2 ? p2->p_pid : 0;
135 td->td_retval[1] = 0;
140 int nprocs = 1; /* process 0 */
142 SYSCTL_INT(_kern, OID_AUTO, lastpid, CTLFLAG_RD, &lastpid, 0,
146 * Random component to lastpid generation. We mix in a random factor to make
147 * it a little harder to predict. We sanity check the modulus value to avoid
148 * doing it in critical paths. Don't let it be too small or we pointlessly
149 * waste randomness entropy, and don't let it be impossibly large. Using a
150 * modulus that is too big causes a LOT more process table scans and slows
151 * down fork processing as the pidchecked caching is defeated.
153 static int randompid = 0;
156 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
160 error = sysctl_wire_old_buffer(req, sizeof(int));
163 sx_xlock(&allproc_lock);
165 error = sysctl_handle_int(oidp, &pid, 0, req);
166 if (error == 0 && req->newptr != NULL) {
167 if (pid < 0 || pid > PID_MAX - 100) /* out of range */
169 else if (pid < 2) /* NOP */
171 else if (pid < 100) /* Make it reasonable */
175 sx_xunlock(&allproc_lock);
179 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
180 0, 0, sysctl_kern_randompid, "I", "Random PID modulus");
183 fork1(td, flags, pages, procp)
189 struct proc *p1, *p2, *pptr;
190 struct proc *newproc;
192 static int curfail, pidchecked = 0;
193 static struct timeval lastfail;
195 struct filedesc_to_leader *fdtol;
197 struct sigacts *newsigacts;
201 /* Can't copy and clear. */
202 if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
208 * Here we don't create a new process, but we divorce
209 * certain parts of a process from itself.
211 if ((flags & RFPROC) == 0) {
212 if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
213 (flags & (RFCFDG | RFFDG))) {
215 if (thread_single(SINGLE_BOUNDARY)) {
222 error = vm_forkproc(td, NULL, NULL, NULL, flags);
227 * Close all file descriptors.
229 if (flags & RFCFDG) {
230 struct filedesc *fdtmp;
231 fdtmp = fdinit(td->td_proc->p_fd);
237 * Unshare file descriptors (from parent).
243 if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
244 (flags & (RFCFDG | RFFDG))) {
255 * We did have single-threading code here
256 * however it proved un-needed and caused problems
259 /* Allocate new proc. */
260 newproc = uma_zalloc(proc_zone, M_WAITOK);
261 if (TAILQ_EMPTY(&newproc->p_threads)) {
262 td2 = thread_alloc();
267 proc_linkup(newproc, td2);
269 td2 = FIRST_THREAD_IN_PROC(newproc);
271 /* Allocate and switch to an alternate kstack if specified. */
273 if (!vm_thread_new_altkstack(td2, pages)) {
278 if ((flags & RFMEM) == 0) {
279 vm2 = vmspace_fork(p1->p_vmspace);
287 mac_proc_init(newproc);
289 knlist_init(&newproc->p_klist, &newproc->p_mtx, NULL, NULL, NULL);
290 STAILQ_INIT(&newproc->p_ktr);
292 /* We have to lock the process tree while we look for a pid. */
293 sx_slock(&proctree_lock);
296 * Although process entries are dynamically created, we still keep
297 * a global limit on the maximum number we will create. Don't allow
298 * a nonprivileged user to use the last ten processes; don't let root
299 * exceed the limit. The variable nprocs is the current number of
300 * processes, maxproc is the limit.
302 sx_xlock(&allproc_lock);
303 if ((nprocs >= maxproc - 10 && priv_check_cred(td->td_ucred,
304 PRIV_MAXPROC, 0) != 0) || nprocs >= maxproc) {
310 * Increment the count of procs running with this uid. Don't allow
311 * a nonprivileged user to exceed their current limit.
313 * XXXRW: Can we avoid privilege here if it's not needed?
315 error = priv_check_cred(td->td_ucred, PRIV_PROC_LIMIT, 0);
317 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1, 0);
320 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1,
321 lim_cur(p1, RLIMIT_NPROC));
330 * Increment the nprocs resource before blocking can occur. There
331 * are hard-limits as to the number of processes that can run.
336 * Find an unused process ID. We remember a range of unused IDs
337 * ready to use (from lastpid+1 through pidchecked-1).
339 * If RFHIGHPID is set (used during system boot), do not allocate
342 trypid = lastpid + 1;
343 if (flags & RFHIGHPID) {
348 trypid += arc4random() % randompid;
352 * If the process ID prototype has wrapped around,
353 * restart somewhat above 0, as the low-numbered procs
354 * tend to include daemons that don't exit.
356 if (trypid >= PID_MAX) {
357 trypid = trypid % PID_MAX;
362 if (trypid >= pidchecked) {
365 pidchecked = PID_MAX;
367 * Scan the active and zombie procs to check whether this pid
368 * is in use. Remember the lowest pid that's greater
369 * than trypid, so we can avoid checking for a while.
371 p2 = LIST_FIRST(&allproc);
373 for (; p2 != NULL; p2 = LIST_NEXT(p2, p_list)) {
374 while (p2->p_pid == trypid ||
375 (p2->p_pgrp != NULL &&
376 (p2->p_pgrp->pg_id == trypid ||
377 (p2->p_session != NULL &&
378 p2->p_session->s_sid == trypid)))) {
380 if (trypid >= pidchecked)
383 if (p2->p_pid > trypid && pidchecked > p2->p_pid)
384 pidchecked = p2->p_pid;
385 if (p2->p_pgrp != NULL) {
386 if (p2->p_pgrp->pg_id > trypid &&
387 pidchecked > p2->p_pgrp->pg_id)
388 pidchecked = p2->p_pgrp->pg_id;
389 if (p2->p_session != NULL &&
390 p2->p_session->s_sid > trypid &&
391 pidchecked > p2->p_session->s_sid)
392 pidchecked = p2->p_session->s_sid;
397 p2 = LIST_FIRST(&zombproc);
401 sx_sunlock(&proctree_lock);
404 * RFHIGHPID does not mess with the lastpid counter during boot.
406 if (flags & RFHIGHPID)
412 p2->p_state = PRS_NEW; /* protect against others */
415 * Allow the scheduler to initialize the child.
420 AUDIT_ARG(pid, p2->p_pid);
421 LIST_INSERT_HEAD(&allproc, p2, p_list);
422 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
427 sx_xunlock(&allproc_lock);
429 bcopy(&p1->p_startcopy, &p2->p_startcopy,
430 __rangeof(struct proc, p_startcopy, p_endcopy));
433 bzero(&p2->p_startzero,
434 __rangeof(struct proc, p_startzero, p_endzero));
436 p2->p_ucred = crhold(td->td_ucred);
440 * Malloc things while we don't hold any locks.
442 if (flags & RFSIGSHARE)
445 newsigacts = sigacts_alloc();
450 if (flags & RFCFDG) {
451 fd = fdinit(p1->p_fd);
453 } else if (flags & RFFDG) {
454 fd = fdcopy(p1->p_fd);
457 fd = fdshare(p1->p_fd);
458 if (p1->p_fdtol == NULL)
460 filedesc_to_leader_alloc(NULL,
463 if ((flags & RFTHREAD) != 0) {
465 * Shared file descriptor table and
466 * shared process leaders.
469 FILEDESC_XLOCK(p1->p_fd);
470 fdtol->fdl_refcount++;
471 FILEDESC_XUNLOCK(p1->p_fd);
474 * Shared file descriptor table, and
475 * different process leaders
477 fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
483 * Make a proc table entry for the new process.
484 * Start by zeroing the section of proc that is zero-initialized,
485 * then copy the section that is copied directly from the parent.
491 bzero(&td2->td_startzero,
492 __rangeof(struct thread, td_startzero, td_endzero));
494 bcopy(&td->td_startcopy, &td2->td_startcopy,
495 __rangeof(struct thread, td_startcopy, td_endcopy));
497 bcopy(&p2->p_comm, &td2->td_name, sizeof(td2->td_name));
498 td2->td_sigstk = td->td_sigstk;
499 td2->td_sigmask = td->td_sigmask;
500 td2->td_flags = TDF_INMEM;
503 * Duplicate sub-structures as needed.
504 * Increase reference counts on shared objects.
506 p2->p_flag = P_INMEM;
507 p2->p_swtick = ticks;
508 if (p1->p_flag & P_PROFIL)
510 td2->td_ucred = crhold(p2->p_ucred);
511 pargs_hold(p2->p_args);
513 if (flags & RFSIGSHARE) {
514 p2->p_sigacts = sigacts_hold(p1->p_sigacts);
516 sigacts_copy(newsigacts, p1->p_sigacts);
517 p2->p_sigacts = newsigacts;
519 if (flags & RFLINUXTHPN)
520 p2->p_sigparent = SIGUSR1;
522 p2->p_sigparent = SIGCHLD;
524 p2->p_textvp = p1->p_textvp;
529 * p_limit is copy-on-write. Bump its refcount.
533 pstats_fork(p1->p_stats, p2->p_stats);
538 /* Bump references to the text vnode (for procfs) */
543 * Set up linkage for kernel based threading.
545 if ((flags & RFTHREAD) != 0) {
546 mtx_lock(&ppeers_lock);
547 p2->p_peers = p1->p_peers;
549 p2->p_leader = p1->p_leader;
550 mtx_unlock(&ppeers_lock);
551 PROC_LOCK(p1->p_leader);
552 if ((p1->p_leader->p_flag & P_WEXIT) != 0) {
553 PROC_UNLOCK(p1->p_leader);
555 * The task leader is exiting, so process p1 is
556 * going to be killed shortly. Since p1 obviously
557 * isn't dead yet, we know that the leader is either
558 * sending SIGKILL's to all the processes in this
559 * task or is sleeping waiting for all the peers to
560 * exit. We let p1 complete the fork, but we need
561 * to go ahead and kill the new process p2 since
562 * the task leader may not get a chance to send
563 * SIGKILL to it. We leave it on the list so that
564 * the task leader will wait for this new process
568 psignal(p2, SIGKILL);
571 PROC_UNLOCK(p1->p_leader);
577 sx_xlock(&proctree_lock);
578 PGRP_LOCK(p1->p_pgrp);
583 * Preserve some more flags in subprocess. P_PROFIL has already
586 p2->p_flag |= p1->p_flag & P_SUGID;
587 td2->td_pflags |= td->td_pflags & TDP_ALTSTACK;
588 SESS_LOCK(p1->p_session);
589 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
590 p2->p_flag |= P_CONTROLT;
591 SESS_UNLOCK(p1->p_session);
592 if (flags & RFPPWAIT)
593 p2->p_flag |= P_PPWAIT;
595 p2->p_pgrp = p1->p_pgrp;
596 LIST_INSERT_AFTER(p1, p2, p_pglist);
597 PGRP_UNLOCK(p1->p_pgrp);
598 LIST_INIT(&p2->p_children);
600 callout_init(&p2->p_itcallout, CALLOUT_MPSAFE);
604 * Copy traceflag and tracefile if enabled.
606 mtx_lock(&ktrace_mtx);
607 KASSERT(p2->p_tracevp == NULL, ("new process has a ktrace vnode"));
608 if (p1->p_traceflag & KTRFAC_INHERIT) {
609 p2->p_traceflag = p1->p_traceflag;
610 if ((p2->p_tracevp = p1->p_tracevp) != NULL) {
612 KASSERT(p1->p_tracecred != NULL,
613 ("ktrace vnode with no cred"));
614 p2->p_tracecred = crhold(p1->p_tracecred);
617 mtx_unlock(&ktrace_mtx);
621 * If PF_FORK is set, the child process inherits the
622 * procfs ioctl flags from its parent.
624 if (p1->p_pfsflags & PF_FORK) {
625 p2->p_stops = p1->p_stops;
626 p2->p_pfsflags = p1->p_pfsflags;
630 * This begins the section where we must prevent the parent
631 * from being swapped.
637 * Attach the new process to its parent.
639 * If RFNOWAIT is set, the newly created process becomes a child
640 * of init. This effectively disassociates the child from the
643 if (flags & RFNOWAIT)
648 LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
649 sx_xunlock(&proctree_lock);
651 /* Inform accounting that we have forked. */
652 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);
680 * Both processes are set up, now check if any loadable modules want
681 * to adjust anything.
682 * What if they have an error? XXX
684 EVENTHANDLER_INVOKE(process_fork, p1, p2, flags);
687 * 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;
695 * If RFSTOPPED not requested, make child runnable and add to
698 if ((flags & RFSTOPPED) == 0) {
701 sched_add(td2, SRQ_BORING);
706 * Now can be swapped.
712 * Tell any interested parties about the new process.
714 KNOTE_LOCKED(&p1->p_klist, NOTE_FORK | p2->p_pid);
719 * Preserve synchronization semantics of vfork. If waiting for
720 * child to exec or exit, set P_PPWAIT on child, and sleep on our
721 * proc (in case of exit).
724 while (p2->p_flag & P_PPWAIT)
725 msleep(p1, &p2->p_mtx, PWAIT, "ppwait", 0);
729 * Return child proc pointer to parent.
734 sx_sunlock(&proctree_lock);
735 if (ppsratecheck(&lastfail, &curfail, 1))
736 printf("maxproc limit exceeded by uid %i, please see tuning(7) and login.conf(5).\n",
737 td->td_ucred->cr_ruid);
738 sx_xunlock(&allproc_lock);
740 mac_proc_destroy(newproc);
743 uma_zfree(proc_zone, newproc);
744 pause("fork", hz / 2);
749 * Handle the return of a child process from fork1(). This function
750 * is called from the MD fork_trampoline() entry point.
753 fork_exit(callout, arg, frame)
754 void (*callout)(void *, struct trapframe *);
756 struct trapframe *frame;
764 KASSERT(p->p_state == PRS_NORMAL, ("executing process is still new"));
766 CTR4(KTR_PROC, "fork_exit: new thread %p (td_sched %p, pid %d, %s)",
767 td, td->td_sched, p->p_pid, td->td_name);
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.
775 if ((dtd = PCPU_GET(deadthread))) {
776 PCPU_SET(deadthread, NULL);
782 * cpu_set_fork_handler intercepts this function call to
783 * have this call a non-return function to stay in kernel mode.
784 * initproc has its own fork handler, but it does return.
786 KASSERT(callout != NULL, ("NULL callout in fork_exit"));
790 * Check if a kernel thread misbehaved and returned from its main
793 if (p->p_flag & P_KTHREAD) {
794 printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
795 td->td_name, p->p_pid);
798 mtx_assert(&Giant, MA_NOTOWNED);
800 EVENTHANDLER_INVOKE(schedtail, p);
804 * Simplified back end of syscall(), used when returning from fork()
805 * directly into user mode. Giant is not held on entry, and must not
806 * be held on return. This function is passed in to fork_exit() as the
807 * first parameter and is called when returning to a new userland process.
810 fork_return(td, frame)
812 struct trapframe *frame;
817 if (KTRPOINT(td, KTR_SYSRET))
818 ktrsysret(SYS_fork, 0, 0);
820 mtx_assert(&Giant, MA_NOTOWNED);