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38 * @(#)kern_fork.c 8.6 (Berkeley) 4/8/94
39 * $FreeBSD: src/sys/kern/kern_fork.c,v 1.72.2.14 2003/06/26 04:15:10 silby Exp $
40 * $DragonFly: src/sys/kern/kern_fork.c,v 1.59 2006/10/20 17:02:16 dillon Exp $
43 #include "opt_ktrace.h"
45 #include <sys/param.h>
46 #include <sys/systm.h>
47 #include <sys/sysproto.h>
48 #include <sys/filedesc.h>
49 #include <sys/kernel.h>
50 #include <sys/sysctl.h>
51 #include <sys/malloc.h>
53 #include <sys/resourcevar.h>
54 #include <sys/vnode.h>
56 #include <sys/ktrace.h>
57 #include <sys/unistd.h>
64 #include <vm/vm_map.h>
65 #include <vm/vm_extern.h>
66 #include <vm/vm_zone.h>
68 #include <sys/vmmeter.h>
70 #include <sys/thread2.h>
72 static MALLOC_DEFINE(M_ATFORK, "atfork", "atfork callback");
75 * These are the stuctures used to create a callout list for things to do
76 * when forking a process
80 TAILQ_ENTRY(forklist) next;
83 TAILQ_HEAD(forklist_head, forklist);
84 static struct forklist_head fork_list = TAILQ_HEAD_INITIALIZER(fork_list);
86 int forksleep; /* Place for fork1() to sleep on. */
90 sys_fork(struct fork_args *uap)
92 struct lwp *lp = curthread->td_lwp;
96 error = fork1(lp, RFFDG | RFPROC | RFPGLOCK, &p2);
98 start_forked_proc(lp, p2);
99 uap->sysmsg_fds[0] = p2->p_pid;
100 uap->sysmsg_fds[1] = 0;
107 sys_vfork(struct vfork_args *uap)
109 struct lwp *lp = curthread->td_lwp;
113 error = fork1(lp, RFFDG | RFPROC | RFPPWAIT | RFMEM | RFPGLOCK, &p2);
115 start_forked_proc(lp, p2);
116 uap->sysmsg_fds[0] = p2->p_pid;
117 uap->sysmsg_fds[1] = 0;
123 * Handle rforks. An rfork may (1) operate on the current process without
124 * creating a new, (2) create a new process that shared the current process's
125 * vmspace, signals, and/or descriptors, or (3) create a new process that does
126 * not share these things (normal fork).
128 * Note that we only call start_forked_proc() if a new process is actually
131 * rfork { int flags }
134 sys_rfork(struct rfork_args *uap)
136 struct lwp *lp = curthread->td_lwp;
140 if ((uap->flags & RFKERNELONLY) != 0)
143 error = fork1(lp, uap->flags | RFPGLOCK, &p2);
146 start_forked_proc(lp, p2);
147 uap->sysmsg_fds[0] = p2 ? p2->p_pid : 0;
148 uap->sysmsg_fds[1] = 0;
154 int nprocs = 1; /* process 0 */
157 fork1(struct lwp *lp1, int flags, struct proc **procp)
159 struct proc *p1 = lp1->lwp_proc;
160 struct proc *p2, *pptr;
165 static int curfail = 0;
166 static struct timeval lastfail;
168 struct filedesc_to_leader *fdtol;
170 if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
174 * Here we don't create a new process, but we divorce
175 * certain parts of a process from itself.
177 if ((flags & RFPROC) == 0) {
179 vm_fork(lp1, 0, flags);
182 * Close all file descriptors.
184 if (flags & RFCFDG) {
185 struct filedesc *fdtmp;
192 * Unshare file descriptors (from parent.)
195 if (p1->p_fd->fd_refcnt > 1) {
196 struct filedesc *newfd;
207 * Interlock against process group signal delivery. If signals
208 * are pending after the interlock is obtained we have to restart
209 * the system call to process the signals. If we don't the child
210 * can miss a pgsignal (such as ^C) sent during the fork.
212 * We can't use CURSIG() here because it will process any STOPs
213 * and cause the process group lock to be held indefinitely. If
214 * a STOP occurs, the fork will be restarted after the CONT.
218 if ((flags & RFPGLOCK) && (pgrp = p1->p_pgrp) != NULL) {
219 lockmgr(&pgrp->pg_lock, LK_SHARED);
227 * Although process entries are dynamically created, we still keep
228 * a global limit on the maximum number we will create. Don't allow
229 * a nonprivileged user to use the last ten processes; don't let root
230 * exceed the limit. The variable nprocs is the current number of
231 * processes, maxproc is the limit.
233 uid = p1->p_ucred->cr_ruid;
234 if ((nprocs >= maxproc - 10 && uid != 0) || nprocs >= maxproc) {
235 if (ppsratecheck(&lastfail, &curfail, 1))
236 printf("maxproc limit exceeded by uid %d, please "
237 "see tuning(7) and login.conf(5).\n", uid);
238 tsleep(&forksleep, 0, "fork", hz / 2);
243 * Increment the nprocs resource before blocking can occur. There
244 * are hard-limits as to the number of processes that can run.
249 * Increment the count of procs running with this uid. Don't allow
250 * a nonprivileged user to exceed their current limit.
252 ok = chgproccnt(p1->p_ucred->cr_ruidinfo, 1,
253 (uid != 0) ? p1->p_rlimit[RLIMIT_NPROC].rlim_cur : 0);
256 * Back out the process count
259 if (ppsratecheck(&lastfail, &curfail, 1))
260 printf("maxproc limit exceeded by uid %d, please "
261 "see tuning(7) and login.conf(5).\n", uid);
262 tsleep(&forksleep, 0, "fork", hz / 2);
267 /* Allocate new proc. */
268 p2 = zalloc(proc_zone);
271 * Setup linkage for kernel based threading XXX lwp
273 if (flags & RFTHREAD) {
274 p2->p_peers = p1->p_peers;
276 p2->p_leader = p1->p_leader;
283 p2->p_vmspace = NULL;
284 p2->p_numposixlocks = 0;
285 p2->p_emuldata = NULL;
286 LIST_INIT(&p2->p_lwps);
292 LIST_INSERT_HEAD(&p2->p_lwps, lp2, lwp_list);
298 * Setting the state to SIDL protects the partially initialized
299 * process once it starts getting hooked into the rest of the system.
302 proc_add_allproc(p2);
305 * Make a proc table entry for the new process.
306 * Start by zeroing the section of proc that is zero-initialized,
307 * then copy the section that is copied directly from the parent.
309 bzero(&p2->p_startzero,
310 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero));
311 bzero(&lp2->lwp_startzero,
312 (unsigned) ((caddr_t)&lp2->lwp_endzero -
313 (caddr_t)&lp2->lwp_startzero));
314 bcopy(&p1->p_startcopy, &p2->p_startcopy,
315 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy));
316 bcopy(&p1->p_lwp.lwp_startcopy, &lp2->lwp_startcopy,
317 (unsigned) ((caddr_t)&lp2->lwp_endcopy -
318 (caddr_t)&lp2->lwp_startcopy));
320 p2->p_aioinfo = NULL;
323 * Duplicate sub-structures as needed.
324 * Increase reference counts on shared objects.
325 * The p_stats and p_sigacts substructs are set in vm_fork.
326 * p_lock is in the copy area and must be cleared.
330 if (p1->p_flag & P_PROFIL)
332 p2->p_ucred = crhold(p1->p_ucred);
334 if (jailed(p2->p_ucred))
335 p2->p_flag |= P_JAILED;
338 p2->p_args->ar_ref++;
340 if (flags & RFSIGSHARE) {
341 p2->p_procsig = p1->p_procsig;
342 p2->p_procsig->ps_refcnt++;
343 if (p1->p_sigacts == &p1->p_addr->u_sigacts) {
344 struct sigacts *newsigacts;
346 /* Create the shared sigacts structure */
347 MALLOC(newsigacts, struct sigacts *,
348 sizeof(struct sigacts), M_SUBPROC, M_WAITOK);
351 * Set p_sigacts to the new shared structure.
352 * Note that this is updating p1->p_sigacts at the
353 * same time, since p_sigacts is just a pointer to
354 * the shared p_procsig->ps_sigacts.
356 p2->p_sigacts = newsigacts;
357 bcopy(&p1->p_addr->u_sigacts, p2->p_sigacts,
358 sizeof(*p2->p_sigacts));
359 *p2->p_sigacts = p1->p_addr->u_sigacts;
363 MALLOC(p2->p_procsig, struct procsig *, sizeof(struct procsig),
364 M_SUBPROC, M_WAITOK);
365 bcopy(p1->p_procsig, p2->p_procsig, sizeof(*p2->p_procsig));
366 p2->p_procsig->ps_refcnt = 1;
367 p2->p_sigacts = NULL; /* finished in vm_fork() */
369 if (flags & RFLINUXTHPN)
370 p2->p_sigparent = SIGUSR1;
372 p2->p_sigparent = SIGCHLD;
374 /* bump references to the text vnode (for procfs) */
375 p2->p_textvp = p1->p_textvp;
380 * Handle file descriptors
382 if (flags & RFCFDG) {
383 p2->p_fd = fdinit(p1);
385 } else if (flags & RFFDG) {
386 p2->p_fd = fdcopy(p1);
389 p2->p_fd = fdshare(p1);
390 if (p1->p_fdtol == NULL)
392 filedesc_to_leader_alloc(NULL,
394 if ((flags & RFTHREAD) != 0) {
396 * Shared file descriptor table and
397 * shared process leaders.
400 fdtol->fdl_refcount++;
403 * Shared file descriptor table, and
404 * different process leaders
406 fdtol = filedesc_to_leader_alloc(p1->p_fdtol, p2);
410 p2->p_limit = plimit_fork(p1->p_limit);
413 * Preserve some more flags in subprocess. P_PROFIL has already
416 p2->p_flag |= p1->p_flag & (P_SUGID | P_ALTSTACK);
417 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
418 p2->p_flag |= P_CONTROLT;
419 if (flags & RFPPWAIT)
420 p2->p_flag |= P_PPWAIT;
423 * Inherit the virtual kernel structure (allows a virtual kernel
424 * to fork to simulate multiple cpus).
426 p2->p_vkernel = NULL;
428 vkernel_inherit(p1, p2);
431 * Once we are on a pglist we may receive signals. XXX we might
432 * race a ^C being sent to the process group by not receiving it
433 * at all prior to this line.
435 LIST_INSERT_AFTER(p1, p2, p_pglist);
438 * Attach the new process to its parent.
440 * If RFNOWAIT is set, the newly created process becomes a child
441 * of init. This effectively disassociates the child from the
444 if (flags & RFNOWAIT)
449 LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
450 LIST_INIT(&p2->p_children);
451 varsymset_init(&p2->p_varsymset, &p1->p_varsymset);
452 callout_init(&p2->p_ithandle);
456 * Copy traceflag and tracefile if enabled. If not inherited,
457 * these were zeroed above but we still could have a trace race
458 * so make sure p2's p_tracenode is NULL.
460 if ((p1->p_traceflag & KTRFAC_INHERIT) && p2->p_tracenode == NULL) {
461 p2->p_traceflag = p1->p_traceflag;
462 p2->p_tracenode = ktrinherit(p1->p_tracenode);
467 * Inherit the scheduler and initialize scheduler-related fields.
468 * Set cpbase to the last timeout that occured (not the upcoming
471 * A critical section is required since a timer IPI can update
472 * scheduler specific data.
475 p2->p_usched = p1->p_usched;
476 lp2->lwp_cpbase = mycpu->gd_schedclock.time -
477 mycpu->gd_schedclock.periodic;
478 p2->p_usched->heuristic_forking(&p1->p_lwp, lp2);
482 * This begins the section where we must prevent the parent
483 * from being swapped.
488 * Finish creating the child process. It will return via a different
489 * execution path later. (ie: directly into user mode)
491 vm_fork(lp1, p2, flags);
492 caps_fork(p1, p2, flags);
494 if (flags == (RFFDG | RFPROC)) {
495 mycpu->gd_cnt.v_forks++;
496 mycpu->gd_cnt.v_forkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
497 } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
498 mycpu->gd_cnt.v_vforks++;
499 mycpu->gd_cnt.v_vforkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
500 } else if (p1 == &proc0) {
501 mycpu->gd_cnt.v_kthreads++;
502 mycpu->gd_cnt.v_kthreadpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
504 mycpu->gd_cnt.v_rforks++;
505 mycpu->gd_cnt.v_rforkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
509 * Both processes are set up, now check if any loadable modules want
510 * to adjust anything.
511 * What if they have an error? XXX
513 TAILQ_FOREACH(ep, &fork_list, next) {
514 (*ep->function)(p1, p2, flags);
518 * Set the start time. Note that the process is not runnable. The
519 * caller is responsible for making it runnable.
521 microtime(&p2->p_start);
522 p2->p_acflag = AFORK;
525 * tell any interested parties about the new process
527 KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid);
530 * Return child proc pointer to parent.
535 lockmgr(&pgrp->pg_lock, LK_RELEASE);
540 * The next two functionms are general routines to handle adding/deleting
541 * items on the fork callout list.
544 * Take the arguments given and put them onto the fork callout list,
545 * However first make sure that it's not already there.
546 * Returns 0 on success or a standard error number.
549 at_fork(forklist_fn function)
554 /* let the programmer know if he's been stupid */
555 if (rm_at_fork(function)) {
556 printf("WARNING: fork callout entry (%p) already present\n",
560 ep = kmalloc(sizeof(*ep), M_ATFORK, M_WAITOK|M_ZERO);
561 ep->function = function;
562 TAILQ_INSERT_TAIL(&fork_list, ep, next);
567 * Scan the exit callout list for the given item and remove it..
568 * Returns the number of items removed (0 or 1)
571 rm_at_fork(forklist_fn function)
575 TAILQ_FOREACH(ep, &fork_list, next) {
576 if (ep->function == function) {
577 TAILQ_REMOVE(&fork_list, ep, next);
586 * Add a forked process to the run queue after any remaining setup, such
587 * as setting the fork handler, has been completed.
590 start_forked_proc(struct lwp *lp1, struct proc *p2)
594 KKASSERT(p2 != NULL && p2->p_nthreads == 1);
596 lp2 = LIST_FIRST(&p2->p_lwps);
599 * Move from SIDL to RUN queue, and activate the process's thread.
600 * Activation of the thread effectively makes the process "a"
601 * current process, so we do not setrunqueue().
603 * YYY setrunqueue works here but we should clean up the trampoline
604 * code so we just schedule the LWKT thread and let the trampoline
605 * deal with the userland scheduler on return to userland.
607 KASSERT(p2->p_stat == SIDL,
608 ("cannot start forked process, bad status: %p", p2));
609 p2->p_usched->resetpriority(lp2);
612 p2->p_usched->setrunqueue(lp2);
616 * Now can be swapped.
618 PRELE(lp1->lwp_proc);
621 * Preserve synchronization semantics of vfork. If waiting for
622 * child to exec or exit, set P_PPWAIT on child, and sleep on our
623 * proc (in case of exit).
625 while (p2->p_flag & P_PPWAIT)
626 tsleep(lp1->lwp_proc, 0, "ppwait", 0);