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38 * @(#)kern_fork.c 8.6 (Berkeley) 4/8/94
39 * $FreeBSD: src/sys/kern/kern_fork.c,v 1.72.2.13 2003/06/06 20:21:32 tegge Exp $
40 * $DragonFly: src/sys/kern/kern_fork.c,v 1.15 2003/07/30 00:19:14 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>
63 #include <vm/vm_map.h>
64 #include <vm/vm_extern.h>
65 #include <vm/vm_zone.h>
67 #include <sys/vmmeter.h>
70 static MALLOC_DEFINE(M_ATFORK, "atfork", "atfork callback");
73 * These are the stuctures used to create a callout list for things to do
74 * when forking a process
78 TAILQ_ENTRY(forklist) next;
81 TAILQ_HEAD(forklist_head, forklist);
82 static struct forklist_head fork_list = TAILQ_HEAD_INITIALIZER(fork_list);
84 int forksleep; /* Place for fork1() to sleep on. */
88 fork(struct fork_args *uap)
90 struct proc *p = curproc;
94 error = fork1(p, RFFDG | RFPROC, &p2);
96 start_forked_proc(p, p2);
97 uap->sysmsg_fds[0] = p2->p_pid;
98 uap->sysmsg_fds[1] = 0;
105 vfork(struct vfork_args *uap)
107 struct proc *p = curproc;
111 error = fork1(p, RFFDG | RFPROC | RFPPWAIT | RFMEM, &p2);
113 start_forked_proc(p, p2);
114 uap->sysmsg_fds[0] = p2->p_pid;
115 uap->sysmsg_fds[1] = 0;
121 rfork(struct rfork_args *uap)
123 struct proc *p = curproc;
127 error = fork1(p, uap->flags, &p2);
129 start_forked_proc(p, p2);
130 uap->sysmsg_fds[0] = p2 ? p2->p_pid : 0;
131 uap->sysmsg_fds[1] = 0;
137 int nprocs = 1; /* process 0 */
138 static int nextpid = 0;
141 * Random component to nextpid generation. We mix in a random factor to make
142 * it a little harder to predict. We sanity check the modulus value to avoid
143 * doing it in critical paths. Don't let it be too small or we pointlessly
144 * waste randomness entropy, and don't let it be impossibly large. Using a
145 * modulus that is too big causes a LOT more process table scans and slows
146 * down fork processing as the pidchecked caching is defeated.
148 static int randompid = 0;
151 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
156 error = sysctl_handle_int(oidp, &pid, 0, req);
157 if (error || !req->newptr)
159 if (pid < 0 || pid > PID_MAX - 100) /* out of range */
161 else if (pid < 2) /* NOP */
163 else if (pid < 100) /* Make it reasonable */
169 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
170 0, 0, sysctl_kern_randompid, "I", "Random PID modulus");
173 fork1(p1, flags, procp)
178 struct proc *p2, *pptr;
180 struct proc *newproc;
182 static int pidchecked = 0;
184 struct filedesc_to_leader *fdtol;
186 if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
190 * Here we don't create a new process, but we divorce
191 * certain parts of a process from itself.
193 if ((flags & RFPROC) == 0) {
195 vm_fork(p1, 0, flags);
198 * Close all file descriptors.
200 if (flags & RFCFDG) {
201 struct filedesc *fdtmp;
208 * Unshare file descriptors (from parent.)
211 if (p1->p_fd->fd_refcnt > 1) {
212 struct filedesc *newfd;
223 * Although process entries are dynamically created, we still keep
224 * a global limit on the maximum number we will create. Don't allow
225 * a nonprivileged user to use the last ten processes; don't let root
226 * exceed the limit. The variable nprocs is the current number of
227 * processes, maxproc is the limit.
229 uid = p1->p_ucred->cr_ruid;
230 if ((nprocs >= maxproc - 10 && uid != 0) || nprocs >= maxproc) {
231 tsleep(&forksleep, 0, "fork", hz / 2);
235 * Increment the nprocs resource before blocking can occur. There
236 * are hard-limits as to the number of processes that can run.
241 * Increment the count of procs running with this uid. Don't allow
242 * a nonprivileged user to exceed their current limit.
244 ok = chgproccnt(p1->p_ucred->cr_ruidinfo, 1,
245 (uid != 0) ? p1->p_rlimit[RLIMIT_NPROC].rlim_cur : 0);
248 * Back out the process count
251 tsleep(&forksleep, 0, "fork", hz / 2);
255 /* Allocate new proc. */
256 newproc = zalloc(proc_zone);
259 * Setup linkage for kernel based threading
261 if((flags & RFTHREAD) != 0) {
262 newproc->p_peers = p1->p_peers;
263 p1->p_peers = newproc;
264 newproc->p_leader = p1->p_leader;
266 newproc->p_peers = 0;
267 newproc->p_leader = newproc;
270 newproc->p_wakeup = 0;
271 newproc->p_vmspace = NULL;
274 * Find an unused process ID. We remember a range of unused IDs
275 * ready to use (from nextpid+1 through pidchecked-1).
279 nextpid += arc4random() % randompid;
282 * If the process ID prototype has wrapped around,
283 * restart somewhat above 0, as the low-numbered procs
284 * tend to include daemons that don't exit.
286 if (nextpid >= PID_MAX) {
287 nextpid = nextpid % PID_MAX;
292 if (nextpid >= pidchecked) {
295 pidchecked = PID_MAX;
297 * Scan the active and zombie procs to check whether this pid
298 * is in use. Remember the lowest pid that's greater
299 * than nextpid, so we can avoid checking for a while.
301 p2 = LIST_FIRST(&allproc);
303 for (; p2 != 0; p2 = LIST_NEXT(p2, p_list)) {
304 while (p2->p_pid == nextpid ||
305 p2->p_pgrp->pg_id == nextpid ||
306 p2->p_session->s_sid == nextpid) {
308 if (nextpid >= pidchecked)
311 if (p2->p_pid > nextpid && pidchecked > p2->p_pid)
312 pidchecked = p2->p_pid;
313 if (p2->p_pgrp->pg_id > nextpid &&
314 pidchecked > p2->p_pgrp->pg_id)
315 pidchecked = p2->p_pgrp->pg_id;
316 if (p2->p_session->s_sid > nextpid &&
317 pidchecked > p2->p_session->s_sid)
318 pidchecked = p2->p_session->s_sid;
322 p2 = LIST_FIRST(&zombproc);
328 p2->p_stat = SIDL; /* protect against others */
330 LIST_INSERT_HEAD(&allproc, p2, p_list);
331 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
334 * Make a proc table entry for the new process.
335 * Start by zeroing the section of proc that is zero-initialized,
336 * then copy the section that is copied directly from the parent.
338 bzero(&p2->p_startzero,
339 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero));
340 bcopy(&p1->p_startcopy, &p2->p_startcopy,
341 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy));
343 p2->p_aioinfo = NULL;
346 * Duplicate sub-structures as needed.
347 * Increase reference counts on shared objects.
348 * The p_stats and p_sigacts substructs are set in vm_fork.
350 * P_CP_RELEASED indicates that the process is starting out in
351 * the kernel (in the fork trampoline). The flag will be converted
352 * to P_CURPROC when the new process calls userret() and attempts
353 * to return to userland
355 p2->p_flag = P_INMEM | P_CP_RELEASED;
356 if (p1->p_flag & P_PROFIL)
358 p2->p_ucred = crhold(p1->p_ucred);
360 if (p2->p_ucred->cr_prison) {
361 p2->p_ucred->cr_prison->pr_ref++;
362 p2->p_flag |= P_JAILED;
366 p2->p_args->ar_ref++;
368 if (flags & RFSIGSHARE) {
369 p2->p_procsig = p1->p_procsig;
370 p2->p_procsig->ps_refcnt++;
371 if (p1->p_sigacts == &p1->p_addr->u_sigacts) {
372 struct sigacts *newsigacts;
375 /* Create the shared sigacts structure */
376 MALLOC(newsigacts, struct sigacts *,
377 sizeof(struct sigacts), M_SUBPROC, M_WAITOK);
380 * Set p_sigacts to the new shared structure.
381 * Note that this is updating p1->p_sigacts at the
382 * same time, since p_sigacts is just a pointer to
383 * the shared p_procsig->ps_sigacts.
385 p2->p_sigacts = newsigacts;
386 bcopy(&p1->p_addr->u_sigacts, p2->p_sigacts,
387 sizeof(*p2->p_sigacts));
388 *p2->p_sigacts = p1->p_addr->u_sigacts;
392 MALLOC(p2->p_procsig, struct procsig *, sizeof(struct procsig),
393 M_SUBPROC, M_WAITOK);
394 bcopy(p1->p_procsig, p2->p_procsig, sizeof(*p2->p_procsig));
395 p2->p_procsig->ps_refcnt = 1;
396 p2->p_sigacts = NULL; /* finished in vm_fork() */
398 if (flags & RFLINUXTHPN)
399 p2->p_sigparent = SIGUSR1;
401 p2->p_sigparent = SIGCHLD;
403 /* bump references to the text vnode (for procfs) */
404 p2->p_textvp = p1->p_textvp;
408 if (flags & RFCFDG) {
409 p2->p_fd = fdinit(p1);
411 } else if (flags & RFFDG) {
412 p2->p_fd = fdcopy(p1);
415 p2->p_fd = fdshare(p1);
416 if (p1->p_fdtol == NULL)
418 filedesc_to_leader_alloc(NULL,
420 if ((flags & RFTHREAD) != 0) {
422 * Shared file descriptor table and
423 * shared process leaders.
426 fdtol->fdl_refcount++;
429 * Shared file descriptor table, and
430 * different process leaders
432 fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
439 * If p_limit is still copy-on-write, bump refcnt,
440 * otherwise get a copy that won't be modified.
441 * (If PL_SHAREMOD is clear, the structure is shared
444 if (p1->p_limit->p_lflags & PL_SHAREMOD)
445 p2->p_limit = limcopy(p1->p_limit);
447 p2->p_limit = p1->p_limit;
448 p2->p_limit->p_refcnt++;
452 * Preserve some more flags in subprocess. P_PROFIL has already
455 p2->p_flag |= p1->p_flag & (P_SUGID | P_ALTSTACK);
456 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
457 p2->p_flag |= P_CONTROLT;
458 if (flags & RFPPWAIT)
459 p2->p_flag |= P_PPWAIT;
461 LIST_INSERT_AFTER(p1, p2, p_pglist);
464 * Attach the new process to its parent.
466 * If RFNOWAIT is set, the newly created process becomes a child
467 * of init. This effectively disassociates the child from the
470 if (flags & RFNOWAIT)
475 LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
476 LIST_INIT(&p2->p_children);
480 * Copy traceflag and tracefile if enabled. If not inherited,
481 * these were zeroed above but we still could have a trace race
482 * so make sure p2's p_tracep is NULL.
484 if ((p1->p_traceflag & KTRFAC_INHERIT) && p2->p_tracep == NULL) {
485 p2->p_traceflag = p1->p_traceflag;
486 if ((p2->p_tracep = p1->p_tracep) != NULL)
492 * set priority of child to be that of parent
494 p2->p_estcpu = p1->p_estcpu;
497 * This begins the section where we must prevent the parent
498 * from being swapped.
503 * Finish creating the child process. It will return via a different
504 * execution path later. (ie: directly into user mode)
506 vm_fork(p1, p2, flags);
508 if (flags == (RFFDG | RFPROC)) {
509 mycpu->gd_cnt.v_forks++;
510 mycpu->gd_cnt.v_forkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
511 } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
512 mycpu->gd_cnt.v_vforks++;
513 mycpu->gd_cnt.v_vforkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
514 } else if (p1 == &proc0) {
515 mycpu->gd_cnt.v_kthreads++;
516 mycpu->gd_cnt.v_kthreadpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
518 mycpu->gd_cnt.v_rforks++;
519 mycpu->gd_cnt.v_rforkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
523 * Both processes are set up, now check if any loadable modules want
524 * to adjust anything.
525 * What if they have an error? XXX
527 TAILQ_FOREACH(ep, &fork_list, next) {
528 (*ep->function)(p1, p2, flags);
532 * Make child runnable and add to run queue.
534 microtime(&(p2->p_stats->p_start));
535 p2->p_acflag = AFORK;
538 * tell any interested parties about the new process
540 KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid);
543 * Return child proc pointer to parent.
550 * The next two functionms are general routines to handle adding/deleting
551 * items on the fork callout list.
554 * Take the arguments given and put them onto the fork callout list,
555 * However first make sure that it's not already there.
556 * Returns 0 on success or a standard error number.
561 forklist_fn function;
566 /* let the programmer know if he's been stupid */
567 if (rm_at_fork(function))
568 printf("WARNING: fork callout entry (%p) already present\n",
571 ep = malloc(sizeof(*ep), M_ATFORK, M_NOWAIT);
574 ep->function = function;
575 TAILQ_INSERT_TAIL(&fork_list, ep, next);
580 * Scan the exit callout list for the given item and remove it..
581 * Returns the number of items removed (0 or 1)
586 forklist_fn function;
590 TAILQ_FOREACH(ep, &fork_list, next) {
591 if (ep->function == function) {
592 TAILQ_REMOVE(&fork_list, ep, next);
601 * Add a forked process to the run queue after any remaining setup, such
602 * as setting the fork handler, has been completed.
606 start_forked_proc(struct proc *p1, struct proc *p2)
609 * Move from SIDL to RUN queue, and activate the process's thread.
610 * Activation of the thread effectively makes the process "a"
611 * current process, so we do not setrunqueue().
613 KASSERT(p2->p_stat == SIDL,
614 ("cannot start forked process, bad status: %p", p2));
621 * Now can be swapped.
626 * Preserve synchronization semantics of vfork. If waiting for
627 * child to exec or exit, set P_PPWAIT on child, and sleep on our
628 * proc (in case of exit).
630 while (p2->p_flag & P_PPWAIT)
631 tsleep(p1, 0, "ppwait", 0);