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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 1.27 2004/06/20 22:29:10 hmp 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>
71 static MALLOC_DEFINE(M_ATFORK, "atfork", "atfork callback");
74 * These are the stuctures used to create a callout list for things to do
75 * when forking a process
79 TAILQ_ENTRY(forklist) next;
82 TAILQ_HEAD(forklist_head, forklist);
83 static struct forklist_head fork_list = TAILQ_HEAD_INITIALIZER(fork_list);
85 int forksleep; /* Place for fork1() to sleep on. */
89 fork(struct fork_args *uap)
91 struct proc *p = curproc;
95 error = fork1(p, RFFDG | RFPROC, &p2);
97 start_forked_proc(p, p2);
98 uap->sysmsg_fds[0] = p2->p_pid;
99 uap->sysmsg_fds[1] = 0;
106 vfork(struct vfork_args *uap)
108 struct proc *p = curproc;
112 error = fork1(p, RFFDG | RFPROC | RFPPWAIT | RFMEM, &p2);
114 start_forked_proc(p, p2);
115 uap->sysmsg_fds[0] = p2->p_pid;
116 uap->sysmsg_fds[1] = 0;
122 * Handle rforks. An rfork may (1) operate on the current process without
123 * creating a new, (2) create a new process that shared the current process's
124 * vmspace, signals, and/or descriptors, or (3) create a new process that does
125 * not share these things (normal fork).
127 * Note that we only call start_forked_proc() if a new process is actually
130 * rfork { int flags }
133 rfork(struct rfork_args *uap)
135 struct proc *p = curproc;
139 if ((uap->flags & RFKERNELONLY) != 0)
142 error = fork1(p, uap->flags, &p2);
145 start_forked_proc(p, p2);
146 uap->sysmsg_fds[0] = p2 ? p2->p_pid : 0;
147 uap->sysmsg_fds[1] = 0;
153 int nprocs = 1; /* process 0 */
154 static int nextpid = 0;
157 * Random component to nextpid generation. We mix in a random factor to make
158 * it a little harder to predict. We sanity check the modulus value to avoid
159 * doing it in critical paths. Don't let it be too small or we pointlessly
160 * waste randomness entropy, and don't let it be impossibly large. Using a
161 * modulus that is too big causes a LOT more process table scans and slows
162 * down fork processing as the pidchecked caching is defeated.
164 static int randompid = 0;
167 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
172 error = sysctl_handle_int(oidp, &pid, 0, req);
173 if (error || !req->newptr)
175 if (pid < 0 || pid > PID_MAX - 100) /* out of range */
177 else if (pid < 2) /* NOP */
179 else if (pid < 100) /* Make it reasonable */
185 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
186 0, 0, sysctl_kern_randompid, "I", "Random PID modulus");
189 fork1(struct proc *p1, int flags, struct proc **procp)
191 struct proc *p2, *pptr;
193 struct proc *newproc;
195 static int curfail = 0, pidchecked = 0;
196 static struct timeval lastfail;
198 struct filedesc_to_leader *fdtol;
200 if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
204 * Here we don't create a new process, but we divorce
205 * certain parts of a process from itself.
207 if ((flags & RFPROC) == 0) {
209 vm_fork(p1, 0, flags);
212 * Close all file descriptors.
214 if (flags & RFCFDG) {
215 struct filedesc *fdtmp;
222 * Unshare file descriptors (from parent.)
225 if (p1->p_fd->fd_refcnt > 1) {
226 struct filedesc *newfd;
237 * Although process entries are dynamically created, we still keep
238 * a global limit on the maximum number we will create. Don't allow
239 * a nonprivileged user to use the last ten processes; don't let root
240 * exceed the limit. The variable nprocs is the current number of
241 * processes, maxproc is the limit.
243 uid = p1->p_ucred->cr_ruid;
244 if ((nprocs >= maxproc - 10 && uid != 0) || nprocs >= maxproc) {
245 if (ppsratecheck(&lastfail, &curfail, 1))
246 printf("maxproc limit exceeded by uid %d, please "
247 "see tuning(7) and login.conf(5).\n", uid);
248 tsleep(&forksleep, 0, "fork", hz / 2);
252 * Increment the nprocs resource before blocking can occur. There
253 * are hard-limits as to the number of processes that can run.
258 * Increment the count of procs running with this uid. Don't allow
259 * a nonprivileged user to exceed their current limit.
261 ok = chgproccnt(p1->p_ucred->cr_ruidinfo, 1,
262 (uid != 0) ? p1->p_rlimit[RLIMIT_NPROC].rlim_cur : 0);
265 * Back out the process count
268 if (ppsratecheck(&lastfail, &curfail, 1))
269 printf("maxproc limit exceeded by uid %d, please "
270 "see tuning(7) and login.conf(5).\n", uid);
271 tsleep(&forksleep, 0, "fork", hz / 2);
275 /* Allocate new proc. */
276 newproc = zalloc(proc_zone);
279 * Setup linkage for kernel based threading
281 if ((flags & RFTHREAD) != 0) {
282 newproc->p_peers = p1->p_peers;
283 p1->p_peers = newproc;
284 newproc->p_leader = p1->p_leader;
286 newproc->p_peers = 0;
287 newproc->p_leader = newproc;
290 newproc->p_wakeup = 0;
291 newproc->p_vmspace = NULL;
292 TAILQ_INIT(&newproc->p_sysmsgq);
295 * Find an unused process ID. We remember a range of unused IDs
296 * ready to use (from nextpid+1 through pidchecked-1).
300 nextpid += arc4random() % randompid;
303 * If the process ID prototype has wrapped around,
304 * restart somewhat above 0, as the low-numbered procs
305 * tend to include daemons that don't exit.
307 if (nextpid >= PID_MAX) {
308 nextpid = nextpid % PID_MAX;
313 if (nextpid >= pidchecked) {
316 pidchecked = PID_MAX;
318 * Scan the active and zombie procs to check whether this pid
319 * is in use. Remember the lowest pid that's greater
320 * than nextpid, so we can avoid checking for a while.
322 p2 = LIST_FIRST(&allproc);
324 for (; p2 != 0; p2 = LIST_NEXT(p2, p_list)) {
325 while (p2->p_pid == nextpid ||
326 p2->p_pgrp->pg_id == nextpid ||
327 p2->p_session->s_sid == nextpid) {
329 if (nextpid >= pidchecked)
332 if (p2->p_pid > nextpid && pidchecked > p2->p_pid)
333 pidchecked = p2->p_pid;
334 if (p2->p_pgrp->pg_id > nextpid &&
335 pidchecked > p2->p_pgrp->pg_id)
336 pidchecked = p2->p_pgrp->pg_id;
337 if (p2->p_session->s_sid > nextpid &&
338 pidchecked > p2->p_session->s_sid)
339 pidchecked = p2->p_session->s_sid;
343 p2 = LIST_FIRST(&zombproc);
349 p2->p_stat = SIDL; /* protect against others */
351 LIST_INSERT_HEAD(&allproc, p2, p_list);
352 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
355 * Make a proc table entry for the new process.
356 * Start by zeroing the section of proc that is zero-initialized,
357 * then copy the section that is copied directly from the parent.
359 bzero(&p2->p_startzero,
360 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero));
361 bcopy(&p1->p_startcopy, &p2->p_startcopy,
362 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy));
364 p2->p_aioinfo = NULL;
367 * Duplicate sub-structures as needed.
368 * Increase reference counts on shared objects.
369 * The p_stats and p_sigacts substructs are set in vm_fork.
371 * P_CP_RELEASED indicates that the process is starting out in
372 * the kernel (in the fork trampoline). The flag will be cleared
373 * when the new process calls userret() and acquires its current
374 * process designation for the return to userland.
376 p2->p_flag = P_INMEM | P_CP_RELEASED;
377 if (p1->p_flag & P_PROFIL)
379 p2->p_ucred = crhold(p1->p_ucred);
381 if (p2->p_ucred->cr_prison) {
382 p2->p_ucred->cr_prison->pr_ref++;
383 p2->p_flag |= P_JAILED;
387 p2->p_args->ar_ref++;
389 if (flags & RFSIGSHARE) {
390 p2->p_procsig = p1->p_procsig;
391 p2->p_procsig->ps_refcnt++;
392 if (p1->p_sigacts == &p1->p_addr->u_sigacts) {
393 struct sigacts *newsigacts;
396 /* Create the shared sigacts structure */
397 MALLOC(newsigacts, struct sigacts *,
398 sizeof(struct sigacts), M_SUBPROC, M_WAITOK);
401 * Set p_sigacts to the new shared structure.
402 * Note that this is updating p1->p_sigacts at the
403 * same time, since p_sigacts is just a pointer to
404 * the shared p_procsig->ps_sigacts.
406 p2->p_sigacts = newsigacts;
407 bcopy(&p1->p_addr->u_sigacts, p2->p_sigacts,
408 sizeof(*p2->p_sigacts));
409 *p2->p_sigacts = p1->p_addr->u_sigacts;
413 MALLOC(p2->p_procsig, struct procsig *, sizeof(struct procsig),
414 M_SUBPROC, M_WAITOK);
415 bcopy(p1->p_procsig, p2->p_procsig, sizeof(*p2->p_procsig));
416 p2->p_procsig->ps_refcnt = 1;
417 p2->p_sigacts = NULL; /* finished in vm_fork() */
419 if (flags & RFLINUXTHPN)
420 p2->p_sigparent = SIGUSR1;
422 p2->p_sigparent = SIGCHLD;
424 /* bump references to the text vnode (for procfs) */
425 p2->p_textvp = p1->p_textvp;
429 if (flags & RFCFDG) {
430 p2->p_fd = fdinit(p1);
432 } else if (flags & RFFDG) {
433 p2->p_fd = fdcopy(p1);
436 p2->p_fd = fdshare(p1);
437 if (p1->p_fdtol == NULL)
439 filedesc_to_leader_alloc(NULL,
441 if ((flags & RFTHREAD) != 0) {
443 * Shared file descriptor table and
444 * shared process leaders.
447 fdtol->fdl_refcount++;
450 * Shared file descriptor table, and
451 * different process leaders
453 fdtol = filedesc_to_leader_alloc(p1->p_fdtol, p2);
459 * If p_limit is still copy-on-write, bump refcnt,
460 * otherwise get a copy that won't be modified.
461 * (If PL_SHAREMOD is clear, the structure is shared
464 if (p1->p_limit->p_lflags & PL_SHAREMOD) {
465 p2->p_limit = limcopy(p1->p_limit);
467 p2->p_limit = p1->p_limit;
468 p2->p_limit->p_refcnt++;
472 * Preserve some more flags in subprocess. P_PROFIL has already
475 p2->p_flag |= p1->p_flag & (P_SUGID | P_ALTSTACK);
476 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
477 p2->p_flag |= P_CONTROLT;
478 if (flags & RFPPWAIT)
479 p2->p_flag |= P_PPWAIT;
481 LIST_INSERT_AFTER(p1, p2, p_pglist);
484 * Attach the new process to its parent.
486 * If RFNOWAIT is set, the newly created process becomes a child
487 * of init. This effectively disassociates the child from the
490 if (flags & RFNOWAIT)
495 LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
496 LIST_INIT(&p2->p_children);
497 varsymset_init(&p2->p_varsymset, &p1->p_varsymset);
501 * Copy traceflag and tracefile if enabled. If not inherited,
502 * these were zeroed above but we still could have a trace race
503 * so make sure p2's p_tracep is NULL.
505 if ((p1->p_traceflag & KTRFAC_INHERIT) && p2->p_tracep == NULL) {
506 p2->p_traceflag = p1->p_traceflag;
507 if ((p2->p_tracep = p1->p_tracep) != NULL)
513 * Give the child process an estcpu skewed towards the batch side
514 * of the parent. This prevents batch programs from glitching
515 * interactive programs when they are first started. If the child
516 * is not a batch program it's priority will be corrected by the
519 p2->p_estcpu_fork = p2->p_estcpu =
520 ESTCPULIM(p1->p_estcpu + ESTCPURAMP);
523 * This begins the section where we must prevent the parent
524 * from being swapped.
529 * Finish creating the child process. It will return via a different
530 * execution path later. (ie: directly into user mode)
532 vm_fork(p1, p2, flags);
533 caps_fork(p1, p2, flags);
535 if (flags == (RFFDG | RFPROC)) {
536 mycpu->gd_cnt.v_forks++;
537 mycpu->gd_cnt.v_forkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
538 } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
539 mycpu->gd_cnt.v_vforks++;
540 mycpu->gd_cnt.v_vforkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
541 } else if (p1 == &proc0) {
542 mycpu->gd_cnt.v_kthreads++;
543 mycpu->gd_cnt.v_kthreadpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
545 mycpu->gd_cnt.v_rforks++;
546 mycpu->gd_cnt.v_rforkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
550 * Both processes are set up, now check if any loadable modules want
551 * to adjust anything.
552 * What if they have an error? XXX
554 TAILQ_FOREACH(ep, &fork_list, next) {
555 (*ep->function)(p1, p2, flags);
559 * Make child runnable and add to run queue.
561 microtime(&p2->p_thread->td_start);
562 p2->p_acflag = AFORK;
565 * tell any interested parties about the new process
567 KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid);
570 * Return child proc pointer to parent.
577 * The next two functionms are general routines to handle adding/deleting
578 * items on the fork callout list.
581 * Take the arguments given and put them onto the fork callout list,
582 * However first make sure that it's not already there.
583 * Returns 0 on success or a standard error number.
586 at_fork(forklist_fn function)
591 /* let the programmer know if he's been stupid */
592 if (rm_at_fork(function)) {
593 printf("WARNING: fork callout entry (%p) already present\n",
597 ep = malloc(sizeof(*ep), M_ATFORK, M_WAITOK|M_ZERO);
598 ep->function = function;
599 TAILQ_INSERT_TAIL(&fork_list, ep, next);
604 * Scan the exit callout list for the given item and remove it..
605 * Returns the number of items removed (0 or 1)
608 rm_at_fork(forklist_fn function)
612 TAILQ_FOREACH(ep, &fork_list, next) {
613 if (ep->function == function) {
614 TAILQ_REMOVE(&fork_list, ep, next);
623 * Add a forked process to the run queue after any remaining setup, such
624 * as setting the fork handler, has been completed.
627 start_forked_proc(struct proc *p1, struct proc *p2)
630 * Move from SIDL to RUN queue, and activate the process's thread.
631 * Activation of the thread effectively makes the process "a"
632 * current process, so we do not setrunqueue().
634 KASSERT(p2 && p2->p_stat == SIDL,
635 ("cannot start forked process, bad status: %p", p2));
643 * Now can be swapped.
648 * Preserve synchronization semantics of vfork. If waiting for
649 * child to exec or exit, set P_PPWAIT on child, and sleep on our
650 * proc (in case of exit).
652 while (p2->p_flag & P_PPWAIT)
653 tsleep(p1, 0, "ppwait", 0);