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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 1.18 2004/02/10 15:31:47 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>
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 curfail = 0, pidchecked = 0;
187 static struct timeval lastfail;
189 struct filedesc_to_leader *fdtol;
191 if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
195 * Here we don't create a new process, but we divorce
196 * certain parts of a process from itself.
198 if ((flags & RFPROC) == 0) {
200 vm_fork(p1, 0, flags);
203 * Close all file descriptors.
205 if (flags & RFCFDG) {
206 struct filedesc *fdtmp;
213 * Unshare file descriptors (from parent.)
216 if (p1->p_fd->fd_refcnt > 1) {
217 struct filedesc *newfd;
228 * Although process entries are dynamically created, we still keep
229 * a global limit on the maximum number we will create. Don't allow
230 * a nonprivileged user to use the last ten processes; don't let root
231 * exceed the limit. The variable nprocs is the current number of
232 * processes, maxproc is the limit.
234 uid = p1->p_ucred->cr_ruid;
235 if ((nprocs >= maxproc - 10 && uid != 0) || nprocs >= maxproc) {
236 if (ppsratecheck(&lastfail, &curfail, 1))
237 printf("maxproc limit exceeded by uid %d, please "
238 "see tuning(7) and login.conf(5).\n", uid);
239 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);
266 /* Allocate new proc. */
267 newproc = zalloc(proc_zone);
270 * Setup linkage for kernel based threading
272 if((flags & RFTHREAD) != 0) {
273 newproc->p_peers = p1->p_peers;
274 p1->p_peers = newproc;
275 newproc->p_leader = p1->p_leader;
277 newproc->p_peers = 0;
278 newproc->p_leader = newproc;
281 newproc->p_wakeup = 0;
282 newproc->p_vmspace = NULL;
285 * Find an unused process ID. We remember a range of unused IDs
286 * ready to use (from nextpid+1 through pidchecked-1).
290 nextpid += arc4random() % randompid;
293 * If the process ID prototype has wrapped around,
294 * restart somewhat above 0, as the low-numbered procs
295 * tend to include daemons that don't exit.
297 if (nextpid >= PID_MAX) {
298 nextpid = nextpid % PID_MAX;
303 if (nextpid >= pidchecked) {
306 pidchecked = PID_MAX;
308 * Scan the active and zombie procs to check whether this pid
309 * is in use. Remember the lowest pid that's greater
310 * than nextpid, so we can avoid checking for a while.
312 p2 = LIST_FIRST(&allproc);
314 for (; p2 != 0; p2 = LIST_NEXT(p2, p_list)) {
315 while (p2->p_pid == nextpid ||
316 p2->p_pgrp->pg_id == nextpid ||
317 p2->p_session->s_sid == nextpid) {
319 if (nextpid >= pidchecked)
322 if (p2->p_pid > nextpid && pidchecked > p2->p_pid)
323 pidchecked = p2->p_pid;
324 if (p2->p_pgrp->pg_id > nextpid &&
325 pidchecked > p2->p_pgrp->pg_id)
326 pidchecked = p2->p_pgrp->pg_id;
327 if (p2->p_session->s_sid > nextpid &&
328 pidchecked > p2->p_session->s_sid)
329 pidchecked = p2->p_session->s_sid;
333 p2 = LIST_FIRST(&zombproc);
339 p2->p_stat = SIDL; /* protect against others */
341 LIST_INSERT_HEAD(&allproc, p2, p_list);
342 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
345 * Make a proc table entry for the new process.
346 * Start by zeroing the section of proc that is zero-initialized,
347 * then copy the section that is copied directly from the parent.
349 bzero(&p2->p_startzero,
350 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero));
351 bcopy(&p1->p_startcopy, &p2->p_startcopy,
352 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy));
354 p2->p_aioinfo = NULL;
357 * Duplicate sub-structures as needed.
358 * Increase reference counts on shared objects.
359 * The p_stats and p_sigacts substructs are set in vm_fork.
361 * P_CP_RELEASED indicates that the process is starting out in
362 * the kernel (in the fork trampoline). The flag will be converted
363 * to P_CURPROC when the new process calls userret() and attempts
364 * to return to userland
366 p2->p_flag = P_INMEM | P_CP_RELEASED;
367 if (p1->p_flag & P_PROFIL)
369 p2->p_ucred = crhold(p1->p_ucred);
371 if (p2->p_ucred->cr_prison) {
372 p2->p_ucred->cr_prison->pr_ref++;
373 p2->p_flag |= P_JAILED;
377 p2->p_args->ar_ref++;
379 if (flags & RFSIGSHARE) {
380 p2->p_procsig = p1->p_procsig;
381 p2->p_procsig->ps_refcnt++;
382 if (p1->p_sigacts == &p1->p_addr->u_sigacts) {
383 struct sigacts *newsigacts;
386 /* Create the shared sigacts structure */
387 MALLOC(newsigacts, struct sigacts *,
388 sizeof(struct sigacts), M_SUBPROC, M_WAITOK);
391 * Set p_sigacts to the new shared structure.
392 * Note that this is updating p1->p_sigacts at the
393 * same time, since p_sigacts is just a pointer to
394 * the shared p_procsig->ps_sigacts.
396 p2->p_sigacts = newsigacts;
397 bcopy(&p1->p_addr->u_sigacts, p2->p_sigacts,
398 sizeof(*p2->p_sigacts));
399 *p2->p_sigacts = p1->p_addr->u_sigacts;
403 MALLOC(p2->p_procsig, struct procsig *, sizeof(struct procsig),
404 M_SUBPROC, M_WAITOK);
405 bcopy(p1->p_procsig, p2->p_procsig, sizeof(*p2->p_procsig));
406 p2->p_procsig->ps_refcnt = 1;
407 p2->p_sigacts = NULL; /* finished in vm_fork() */
409 if (flags & RFLINUXTHPN)
410 p2->p_sigparent = SIGUSR1;
412 p2->p_sigparent = SIGCHLD;
414 /* bump references to the text vnode (for procfs) */
415 p2->p_textvp = p1->p_textvp;
419 if (flags & RFCFDG) {
420 p2->p_fd = fdinit(p1);
422 } else if (flags & RFFDG) {
423 p2->p_fd = fdcopy(p1);
426 p2->p_fd = fdshare(p1);
427 if (p1->p_fdtol == NULL)
429 filedesc_to_leader_alloc(NULL,
431 if ((flags & RFTHREAD) != 0) {
433 * Shared file descriptor table and
434 * shared process leaders.
437 fdtol->fdl_refcount++;
440 * Shared file descriptor table, and
441 * different process leaders
443 fdtol = filedesc_to_leader_alloc(p1->p_fdtol, p2);
449 * If p_limit is still copy-on-write, bump refcnt,
450 * otherwise get a copy that won't be modified.
451 * (If PL_SHAREMOD is clear, the structure is shared
454 if (p1->p_limit->p_lflags & PL_SHAREMOD)
455 p2->p_limit = limcopy(p1->p_limit);
457 p2->p_limit = p1->p_limit;
458 p2->p_limit->p_refcnt++;
462 * Preserve some more flags in subprocess. P_PROFIL has already
465 p2->p_flag |= p1->p_flag & (P_SUGID | P_ALTSTACK);
466 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
467 p2->p_flag |= P_CONTROLT;
468 if (flags & RFPPWAIT)
469 p2->p_flag |= P_PPWAIT;
471 LIST_INSERT_AFTER(p1, p2, p_pglist);
474 * Attach the new process to its parent.
476 * If RFNOWAIT is set, the newly created process becomes a child
477 * of init. This effectively disassociates the child from the
480 if (flags & RFNOWAIT)
485 LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
486 LIST_INIT(&p2->p_children);
487 varsymset_init(&p2->p_varsymset, &p1->p_varsymset);
491 * Copy traceflag and tracefile if enabled. If not inherited,
492 * these were zeroed above but we still could have a trace race
493 * so make sure p2's p_tracep is NULL.
495 if ((p1->p_traceflag & KTRFAC_INHERIT) && p2->p_tracep == NULL) {
496 p2->p_traceflag = p1->p_traceflag;
497 if ((p2->p_tracep = p1->p_tracep) != NULL)
503 * set priority of child to be that of parent
505 p2->p_estcpu = p1->p_estcpu;
508 * This begins the section where we must prevent the parent
509 * from being swapped.
514 * Finish creating the child process. It will return via a different
515 * execution path later. (ie: directly into user mode)
517 vm_fork(p1, p2, flags);
519 if (flags == (RFFDG | RFPROC)) {
520 mycpu->gd_cnt.v_forks++;
521 mycpu->gd_cnt.v_forkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
522 } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
523 mycpu->gd_cnt.v_vforks++;
524 mycpu->gd_cnt.v_vforkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
525 } else if (p1 == &proc0) {
526 mycpu->gd_cnt.v_kthreads++;
527 mycpu->gd_cnt.v_kthreadpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
529 mycpu->gd_cnt.v_rforks++;
530 mycpu->gd_cnt.v_rforkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize;
534 * Both processes are set up, now check if any loadable modules want
535 * to adjust anything.
536 * What if they have an error? XXX
538 TAILQ_FOREACH(ep, &fork_list, next) {
539 (*ep->function)(p1, p2, flags);
543 * Make child runnable and add to run queue.
545 microtime(&(p2->p_stats->p_start));
546 p2->p_acflag = AFORK;
549 * tell any interested parties about the new process
551 KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid);
554 * Return child proc pointer to parent.
561 * The next two functionms are general routines to handle adding/deleting
562 * items on the fork callout list.
565 * Take the arguments given and put them onto the fork callout list,
566 * However first make sure that it's not already there.
567 * Returns 0 on success or a standard error number.
572 forklist_fn function;
577 /* let the programmer know if he's been stupid */
578 if (rm_at_fork(function))
579 printf("WARNING: fork callout entry (%p) already present\n",
582 ep = malloc(sizeof(*ep), M_ATFORK, M_NOWAIT);
585 ep->function = function;
586 TAILQ_INSERT_TAIL(&fork_list, ep, next);
591 * Scan the exit callout list for the given item and remove it..
592 * Returns the number of items removed (0 or 1)
597 forklist_fn function;
601 TAILQ_FOREACH(ep, &fork_list, next) {
602 if (ep->function == function) {
603 TAILQ_REMOVE(&fork_list, ep, next);
612 * Add a forked process to the run queue after any remaining setup, such
613 * as setting the fork handler, has been completed.
617 start_forked_proc(struct proc *p1, struct proc *p2)
620 * Move from SIDL to RUN queue, and activate the process's thread.
621 * Activation of the thread effectively makes the process "a"
622 * current process, so we do not setrunqueue().
624 KASSERT(p2->p_stat == SIDL,
625 ("cannot start forked process, bad status: %p", p2));
632 * Now can be swapped.
637 * Preserve synchronization semantics of vfork. If waiting for
638 * child to exec or exit, set P_PPWAIT on child, and sleep on our
639 * proc (in case of exit).
641 while (p2->p_flag & P_PPWAIT)
642 tsleep(p1, 0, "ppwait", 0);