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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 1.17 2003/11/27 19:57:37 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 /* Don't allow kernel only flags */
128 if ((uap->flags & RFKERNELONLY) != 0)
131 error = fork1(p, uap->flags, &p2);
133 start_forked_proc(p, p2);
134 uap->sysmsg_fds[0] = p2 ? p2->p_pid : 0;
135 uap->sysmsg_fds[1] = 0;
141 int nprocs = 1; /* process 0 */
142 static int nextpid = 0;
145 * Random component to nextpid generation. We mix in a random factor to make
146 * it a little harder to predict. We sanity check the modulus value to avoid
147 * doing it in critical paths. Don't let it be too small or we pointlessly
148 * waste randomness entropy, and don't let it be impossibly large. Using a
149 * modulus that is too big causes a LOT more process table scans and slows
150 * down fork processing as the pidchecked caching is defeated.
152 static int randompid = 0;
155 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
160 error = sysctl_handle_int(oidp, &pid, 0, req);
161 if (error || !req->newptr)
163 if (pid < 0 || pid > PID_MAX - 100) /* out of range */
165 else if (pid < 2) /* NOP */
167 else if (pid < 100) /* Make it reasonable */
173 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
174 0, 0, sysctl_kern_randompid, "I", "Random PID modulus");
177 fork1(p1, flags, procp)
182 struct proc *p2, *pptr;
184 struct proc *newproc;
186 static int pidchecked = 0;
188 struct filedesc_to_leader *fdtol;
190 if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
194 * Here we don't create a new process, but we divorce
195 * certain parts of a process from itself.
197 if ((flags & RFPROC) == 0) {
199 vm_fork(p1, 0, flags);
202 * Close all file descriptors.
204 if (flags & RFCFDG) {
205 struct filedesc *fdtmp;
212 * Unshare file descriptors (from parent.)
215 if (p1->p_fd->fd_refcnt > 1) {
216 struct filedesc *newfd;
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 tsleep(&forksleep, 0, "fork", hz / 2);
239 * Increment the nprocs resource before blocking can occur. There
240 * are hard-limits as to the number of processes that can run.
245 * Increment the count of procs running with this uid. Don't allow
246 * a nonprivileged user to exceed their current limit.
248 ok = chgproccnt(p1->p_ucred->cr_ruidinfo, 1,
249 (uid != 0) ? p1->p_rlimit[RLIMIT_NPROC].rlim_cur : 0);
252 * Back out the process count
255 tsleep(&forksleep, 0, "fork", hz / 2);
259 /* Allocate new proc. */
260 newproc = zalloc(proc_zone);
263 * Setup linkage for kernel based threading
265 if((flags & RFTHREAD) != 0) {
266 newproc->p_peers = p1->p_peers;
267 p1->p_peers = newproc;
268 newproc->p_leader = p1->p_leader;
270 newproc->p_peers = 0;
271 newproc->p_leader = newproc;
274 newproc->p_wakeup = 0;
275 newproc->p_vmspace = NULL;
278 * Find an unused process ID. We remember a range of unused IDs
279 * ready to use (from nextpid+1 through pidchecked-1).
283 nextpid += arc4random() % randompid;
286 * If the process ID prototype has wrapped around,
287 * restart somewhat above 0, as the low-numbered procs
288 * tend to include daemons that don't exit.
290 if (nextpid >= PID_MAX) {
291 nextpid = nextpid % PID_MAX;
296 if (nextpid >= pidchecked) {
299 pidchecked = PID_MAX;
301 * Scan the active and zombie procs to check whether this pid
302 * is in use. Remember the lowest pid that's greater
303 * than nextpid, so we can avoid checking for a while.
305 p2 = LIST_FIRST(&allproc);
307 for (; p2 != 0; p2 = LIST_NEXT(p2, p_list)) {
308 while (p2->p_pid == nextpid ||
309 p2->p_pgrp->pg_id == nextpid ||
310 p2->p_session->s_sid == nextpid) {
312 if (nextpid >= pidchecked)
315 if (p2->p_pid > nextpid && pidchecked > p2->p_pid)
316 pidchecked = p2->p_pid;
317 if (p2->p_pgrp->pg_id > nextpid &&
318 pidchecked > p2->p_pgrp->pg_id)
319 pidchecked = p2->p_pgrp->pg_id;
320 if (p2->p_session->s_sid > nextpid &&
321 pidchecked > p2->p_session->s_sid)
322 pidchecked = p2->p_session->s_sid;
326 p2 = LIST_FIRST(&zombproc);
332 p2->p_stat = SIDL; /* protect against others */
334 LIST_INSERT_HEAD(&allproc, p2, p_list);
335 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
338 * Make a proc table entry for the new process.
339 * Start by zeroing the section of proc that is zero-initialized,
340 * then copy the section that is copied directly from the parent.
342 bzero(&p2->p_startzero,
343 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero));
344 bcopy(&p1->p_startcopy, &p2->p_startcopy,
345 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy));
347 p2->p_aioinfo = NULL;
350 * Duplicate sub-structures as needed.
351 * Increase reference counts on shared objects.
352 * The p_stats and p_sigacts substructs are set in vm_fork.
354 * P_CP_RELEASED indicates that the process is starting out in
355 * the kernel (in the fork trampoline). The flag will be converted
356 * to P_CURPROC when the new process calls userret() and attempts
357 * to return to userland
359 p2->p_flag = P_INMEM | P_CP_RELEASED;
360 if (p1->p_flag & P_PROFIL)
362 p2->p_ucred = crhold(p1->p_ucred);
364 if (p2->p_ucred->cr_prison) {
365 p2->p_ucred->cr_prison->pr_ref++;
366 p2->p_flag |= P_JAILED;
370 p2->p_args->ar_ref++;
372 if (flags & RFSIGSHARE) {
373 p2->p_procsig = p1->p_procsig;
374 p2->p_procsig->ps_refcnt++;
375 if (p1->p_sigacts == &p1->p_addr->u_sigacts) {
376 struct sigacts *newsigacts;
379 /* Create the shared sigacts structure */
380 MALLOC(newsigacts, struct sigacts *,
381 sizeof(struct sigacts), M_SUBPROC, M_WAITOK);
384 * Set p_sigacts to the new shared structure.
385 * Note that this is updating p1->p_sigacts at the
386 * same time, since p_sigacts is just a pointer to
387 * the shared p_procsig->ps_sigacts.
389 p2->p_sigacts = newsigacts;
390 bcopy(&p1->p_addr->u_sigacts, p2->p_sigacts,
391 sizeof(*p2->p_sigacts));
392 *p2->p_sigacts = p1->p_addr->u_sigacts;
396 MALLOC(p2->p_procsig, struct procsig *, sizeof(struct procsig),
397 M_SUBPROC, M_WAITOK);
398 bcopy(p1->p_procsig, p2->p_procsig, sizeof(*p2->p_procsig));
399 p2->p_procsig->ps_refcnt = 1;
400 p2->p_sigacts = NULL; /* finished in vm_fork() */
402 if (flags & RFLINUXTHPN)
403 p2->p_sigparent = SIGUSR1;
405 p2->p_sigparent = SIGCHLD;
407 /* bump references to the text vnode (for procfs) */
408 p2->p_textvp = p1->p_textvp;
412 if (flags & RFCFDG) {
413 p2->p_fd = fdinit(p1);
415 } else if (flags & RFFDG) {
416 p2->p_fd = fdcopy(p1);
419 p2->p_fd = fdshare(p1);
420 if (p1->p_fdtol == NULL)
422 filedesc_to_leader_alloc(NULL,
424 if ((flags & RFTHREAD) != 0) {
426 * Shared file descriptor table and
427 * shared process leaders.
430 fdtol->fdl_refcount++;
433 * Shared file descriptor table, and
434 * different process leaders
436 fdtol = filedesc_to_leader_alloc(p1->p_fdtol, p2);
442 * If p_limit is still copy-on-write, bump refcnt,
443 * otherwise get a copy that won't be modified.
444 * (If PL_SHAREMOD is clear, the structure is shared
447 if (p1->p_limit->p_lflags & PL_SHAREMOD)
448 p2->p_limit = limcopy(p1->p_limit);
450 p2->p_limit = p1->p_limit;
451 p2->p_limit->p_refcnt++;
455 * Preserve some more flags in subprocess. P_PROFIL has already
458 p2->p_flag |= p1->p_flag & (P_SUGID | P_ALTSTACK);
459 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
460 p2->p_flag |= P_CONTROLT;
461 if (flags & RFPPWAIT)
462 p2->p_flag |= P_PPWAIT;
464 LIST_INSERT_AFTER(p1, p2, p_pglist);
467 * Attach the new process to its parent.
469 * If RFNOWAIT is set, the newly created process becomes a child
470 * of init. This effectively disassociates the child from the
473 if (flags & RFNOWAIT)
478 LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
479 LIST_INIT(&p2->p_children);
480 varsymset_init(&p2->p_varsymset, &p1->p_varsymset);
484 * Copy traceflag and tracefile if enabled. If not inherited,
485 * these were zeroed above but we still could have a trace race
486 * so make sure p2's p_tracep is NULL.
488 if ((p1->p_traceflag & KTRFAC_INHERIT) && p2->p_tracep == NULL) {
489 p2->p_traceflag = p1->p_traceflag;
490 if ((p2->p_tracep = p1->p_tracep) != NULL)
496 * set priority of child to be that of parent
498 p2->p_estcpu = p1->p_estcpu;
501 * This begins the section where we must prevent the parent
502 * from being swapped.
507 * Finish creating the child process. It will return via a different
508 * execution path later. (ie: directly into user mode)
510 vm_fork(p1, p2, flags);
512 if (flags == (RFFDG | RFPROC)) {
513 mycpu->gd_cnt.v_forks++;
514 mycpu->gd_cnt.v_forkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
515 } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
516 mycpu->gd_cnt.v_vforks++;
517 mycpu->gd_cnt.v_vforkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
518 } else if (p1 == &proc0) {
519 mycpu->gd_cnt.v_kthreads++;
520 mycpu->gd_cnt.v_kthreadpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
522 mycpu->gd_cnt.v_rforks++;
523 mycpu->gd_cnt.v_rforkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
527 * Both processes are set up, now check if any loadable modules want
528 * to adjust anything.
529 * What if they have an error? XXX
531 TAILQ_FOREACH(ep, &fork_list, next) {
532 (*ep->function)(p1, p2, flags);
536 * Make child runnable and add to run queue.
538 microtime(&(p2->p_stats->p_start));
539 p2->p_acflag = AFORK;
542 * tell any interested parties about the new process
544 KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid);
547 * Return child proc pointer to parent.
554 * The next two functionms are general routines to handle adding/deleting
555 * items on the fork callout list.
558 * Take the arguments given and put them onto the fork callout list,
559 * However first make sure that it's not already there.
560 * Returns 0 on success or a standard error number.
565 forklist_fn function;
570 /* let the programmer know if he's been stupid */
571 if (rm_at_fork(function))
572 printf("WARNING: fork callout entry (%p) already present\n",
575 ep = malloc(sizeof(*ep), M_ATFORK, M_NOWAIT);
578 ep->function = function;
579 TAILQ_INSERT_TAIL(&fork_list, ep, next);
584 * Scan the exit callout list for the given item and remove it..
585 * Returns the number of items removed (0 or 1)
590 forklist_fn function;
594 TAILQ_FOREACH(ep, &fork_list, next) {
595 if (ep->function == function) {
596 TAILQ_REMOVE(&fork_list, ep, next);
605 * Add a forked process to the run queue after any remaining setup, such
606 * as setting the fork handler, has been completed.
610 start_forked_proc(struct proc *p1, struct proc *p2)
613 * Move from SIDL to RUN queue, and activate the process's thread.
614 * Activation of the thread effectively makes the process "a"
615 * current process, so we do not setrunqueue().
617 KASSERT(p2->p_stat == SIDL,
618 ("cannot start forked process, bad status: %p", p2));
625 * Now can be swapped.
630 * Preserve synchronization semantics of vfork. If waiting for
631 * child to exec or exit, set P_PPWAIT on child, and sleep on our
632 * proc (in case of exit).
634 while (p2->p_flag & P_PPWAIT)
635 tsleep(p1, 0, "ppwait", 0);