FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_fork.c
1 /* $NetBSD: kern_fork.c,v 1.121.2.2 2005/05/23 19:09:56 riz Exp $ */
2
3 /*-
4 * Copyright (c) 1999, 2001, 2004 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
9 * NASA Ames Research Center.
10 * This code is derived from software contributed to The NetBSD Foundation
11 * by Charles M. Hannum.
12 *
13 * Redistribution and use in source and binary forms, with or without
14 * modification, are permitted provided that the following conditions
15 * are met:
16 * 1. Redistributions of source code must retain the above copyright
17 * notice, this list of conditions and the following disclaimer.
18 * 2. Redistributions in binary form must reproduce the above copyright
19 * notice, this list of conditions and the following disclaimer in the
20 * documentation and/or other materials provided with the distribution.
21 * 3. All advertising materials mentioning features or use of this software
22 * must display the following acknowledgement:
23 * This product includes software developed by the NetBSD
24 * Foundation, Inc. and its contributors.
25 * 4. Neither the name of The NetBSD Foundation nor the names of its
26 * contributors may be used to endorse or promote products derived
27 * from this software without specific prior written permission.
28 *
29 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
30 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
31 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
32 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
33 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
34 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
35 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
36 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
37 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
38 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
39 * POSSIBILITY OF SUCH DAMAGE.
40 */
41
42 /*
43 * Copyright (c) 1982, 1986, 1989, 1991, 1993
44 * The Regents of the University of California. All rights reserved.
45 * (c) UNIX System Laboratories, Inc.
46 * All or some portions of this file are derived from material licensed
47 * to the University of California by American Telephone and Telegraph
48 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
49 * the permission of UNIX System Laboratories, Inc.
50 *
51 * Redistribution and use in source and binary forms, with or without
52 * modification, are permitted provided that the following conditions
53 * are met:
54 * 1. Redistributions of source code must retain the above copyright
55 * notice, this list of conditions and the following disclaimer.
56 * 2. Redistributions in binary form must reproduce the above copyright
57 * notice, this list of conditions and the following disclaimer in the
58 * documentation and/or other materials provided with the distribution.
59 * 3. Neither the name of the University nor the names of its contributors
60 * may be used to endorse or promote products derived from this software
61 * without specific prior written permission.
62 *
63 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
64 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
65 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
66 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
67 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
68 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
69 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
70 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
71 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
72 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
73 * SUCH DAMAGE.
74 *
75 * @(#)kern_fork.c 8.8 (Berkeley) 2/14/95
76 */
77
78 #include <sys/cdefs.h>
79 __KERNEL_RCSID(0, "$NetBSD: kern_fork.c,v 1.121.2.2 2005/05/23 19:09:56 riz Exp $");
80
81 #include "opt_ktrace.h"
82 #include "opt_systrace.h"
83 #include "opt_multiprocessor.h"
84
85 #include <sys/param.h>
86 #include <sys/systm.h>
87 #include <sys/filedesc.h>
88 #include <sys/kernel.h>
89 #include <sys/malloc.h>
90 #include <sys/pool.h>
91 #include <sys/mount.h>
92 #include <sys/proc.h>
93 #include <sys/ras.h>
94 #include <sys/resourcevar.h>
95 #include <sys/vnode.h>
96 #include <sys/file.h>
97 #include <sys/acct.h>
98 #include <sys/ktrace.h>
99 #include <sys/vmmeter.h>
100 #include <sys/sched.h>
101 #include <sys/signalvar.h>
102 #include <sys/systrace.h>
103
104 #include <sys/sa.h>
105 #include <sys/syscallargs.h>
106
107 #include <uvm/uvm_extern.h>
108
109
110 int nprocs = 1; /* process 0 */
111
112 /*
113 * Number of ticks to sleep if fork() would fail due to process hitting
114 * limits. Exported in miliseconds to userland via sysctl.
115 */
116 int forkfsleep = 0;
117
118 /*ARGSUSED*/
119 int
120 sys_fork(struct lwp *l, void *v, register_t *retval)
121 {
122
123 return (fork1(l, 0, SIGCHLD, NULL, 0, NULL, NULL, retval, NULL));
124 }
125
126 /*
127 * vfork(2) system call compatible with 4.4BSD (i.e. BSD with Mach VM).
128 * Address space is not shared, but parent is blocked until child exit.
129 */
130 /*ARGSUSED*/
131 int
132 sys_vfork(struct lwp *l, void *v, register_t *retval)
133 {
134
135 return (fork1(l, FORK_PPWAIT, SIGCHLD, NULL, 0, NULL, NULL,
136 retval, NULL));
137 }
138
139 /*
140 * New vfork(2) system call for NetBSD, which implements original 3BSD vfork(2)
141 * semantics. Address space is shared, and parent is blocked until child exit.
142 */
143 /*ARGSUSED*/
144 int
145 sys___vfork14(struct lwp *l, void *v, register_t *retval)
146 {
147
148 return (fork1(l, FORK_PPWAIT|FORK_SHAREVM, SIGCHLD, NULL, 0,
149 NULL, NULL, retval, NULL));
150 }
151
152 /*
153 * Linux-compatible __clone(2) system call.
154 */
155 int
156 sys___clone(struct lwp *l, void *v, register_t *retval)
157 {
158 struct sys___clone_args /* {
159 syscallarg(int) flags;
160 syscallarg(void *) stack;
161 } */ *uap = v;
162 int flags, sig;
163
164 /*
165 * We don't support the CLONE_PID or CLONE_PTRACE flags.
166 */
167 if (SCARG(uap, flags) & (CLONE_PID|CLONE_PTRACE))
168 return (EINVAL);
169
170 /*
171 * Linux enforces CLONE_VM with CLONE_SIGHAND, do same.
172 */
173 if (SCARG(uap, flags) & CLONE_SIGHAND
174 && (SCARG(uap, flags) & CLONE_VM) == 0)
175 return (EINVAL);
176
177 flags = 0;
178
179 if (SCARG(uap, flags) & CLONE_VM)
180 flags |= FORK_SHAREVM;
181 if (SCARG(uap, flags) & CLONE_FS)
182 flags |= FORK_SHARECWD;
183 if (SCARG(uap, flags) & CLONE_FILES)
184 flags |= FORK_SHAREFILES;
185 if (SCARG(uap, flags) & CLONE_SIGHAND)
186 flags |= FORK_SHARESIGS;
187 if (SCARG(uap, flags) & CLONE_VFORK)
188 flags |= FORK_PPWAIT;
189
190 sig = SCARG(uap, flags) & CLONE_CSIGNAL;
191 if (sig < 0 || sig >= _NSIG)
192 return (EINVAL);
193
194 /*
195 * Note that the Linux API does not provide a portable way of
196 * specifying the stack area; the caller must know if the stack
197 * grows up or down. So, we pass a stack size of 0, so that the
198 * code that makes this adjustment is a noop.
199 */
200 return (fork1(l, flags, sig, SCARG(uap, stack), 0,
201 NULL, NULL, retval, NULL));
202 }
203
204 /* print the 'table full' message once per 10 seconds */
205 struct timeval fork_tfmrate = { 10, 0 };
206
207 int
208 fork1(struct lwp *l1, int flags, int exitsig, void *stack, size_t stacksize,
209 void (*func)(void *), void *arg, register_t *retval,
210 struct proc **rnewprocp)
211 {
212 struct proc *p1, *p2, *parent;
213 uid_t uid;
214 struct lwp *l2;
215 int count, s;
216 vaddr_t uaddr;
217 boolean_t inmem;
218
219 /*
220 * Although process entries are dynamically created, we still keep
221 * a global limit on the maximum number we will create. Don't allow
222 * a nonprivileged user to use the last few processes; don't let root
223 * exceed the limit. The variable nprocs is the current number of
224 * processes, maxproc is the limit.
225 */
226 p1 = l1->l_proc;
227 uid = p1->p_cred->p_ruid;
228 if (__predict_false((nprocs >= maxproc - 5 && uid != 0) ||
229 nprocs >= maxproc)) {
230 static struct timeval lasttfm;
231
232 if (ratecheck(&lasttfm, &fork_tfmrate))
233 tablefull("proc", "increase kern.maxproc or NPROC");
234 if (forkfsleep)
235 (void)tsleep(&nprocs, PUSER, "forkmx", forkfsleep);
236 return (EAGAIN);
237 }
238 nprocs++;
239
240 /*
241 * Increment the count of procs running with this uid. Don't allow
242 * a nonprivileged user to exceed their current limit.
243 */
244 count = chgproccnt(uid, 1);
245 if (__predict_false(uid != 0 && count >
246 p1->p_rlimit[RLIMIT_NPROC].rlim_cur)) {
247 (void)chgproccnt(uid, -1);
248 nprocs--;
249 if (forkfsleep)
250 (void)tsleep(&nprocs, PUSER, "forkulim", forkfsleep);
251 return (EAGAIN);
252 }
253
254 /*
255 * Allocate virtual address space for the U-area now, while it
256 * is still easy to abort the fork operation if we're out of
257 * kernel virtual address space. The actual U-area pages will
258 * be allocated and wired in uvm_fork() if needed.
259 */
260
261 inmem = uvm_uarea_alloc(&uaddr);
262 if (__predict_false(uaddr == 0)) {
263 (void)chgproccnt(uid, -1);
264 nprocs--;
265 return (ENOMEM);
266 }
267
268 /*
269 * We are now committed to the fork. From here on, we may
270 * block on resources, but resource allocation may NOT fail.
271 */
272
273 /* Allocate new proc. */
274 p2 = proc_alloc();
275
276 /*
277 * Make a proc table entry for the new process.
278 * Start by zeroing the section of proc that is zero-initialized,
279 * then copy the section that is copied directly from the parent.
280 */
281 memset(&p2->p_startzero, 0,
282 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero));
283 memcpy(&p2->p_startcopy, &p1->p_startcopy,
284 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy));
285
286 simple_lock_init(&p2->p_sigctx.ps_silock);
287 CIRCLEQ_INIT(&p2->p_sigctx.ps_siginfo);
288 simple_lock_init(&p2->p_lock);
289 LIST_INIT(&p2->p_lwps);
290
291 /*
292 * Duplicate sub-structures as needed.
293 * Increase reference counts on shared objects.
294 * The p_stats and p_sigacts substructs are set in uvm_fork().
295 * Inherit SUGID, STOPFORK and STOPEXEC flags.
296 */
297 p2->p_flag = p1->p_flag & (P_SUGID | P_STOPFORK | P_STOPEXEC);
298 p2->p_emul = p1->p_emul;
299 p2->p_execsw = p1->p_execsw;
300
301 if (p1->p_flag & P_PROFIL)
302 startprofclock(p2);
303 p2->p_cred = pool_get(&pcred_pool, PR_WAITOK);
304 memcpy(p2->p_cred, p1->p_cred, sizeof(*p2->p_cred));
305 p2->p_cred->p_refcnt = 1;
306 crhold(p1->p_ucred);
307
308 LIST_INIT(&p2->p_raslist);
309 #if defined(__HAVE_RAS)
310 ras_fork(p1, p2);
311 #endif
312
313 /* bump references to the text vnode (for procfs) */
314 p2->p_textvp = p1->p_textvp;
315 if (p2->p_textvp)
316 VREF(p2->p_textvp);
317
318 if (flags & FORK_SHAREFILES)
319 fdshare(p1, p2);
320 else if (flags & FORK_CLEANFILES)
321 p2->p_fd = fdinit(p1);
322 else
323 p2->p_fd = fdcopy(p1);
324
325 if (flags & FORK_SHARECWD)
326 cwdshare(p1, p2);
327 else
328 p2->p_cwdi = cwdinit(p1);
329
330 /*
331 * If p_limit is still copy-on-write, bump refcnt,
332 * otherwise get a copy that won't be modified.
333 * (If PL_SHAREMOD is clear, the structure is shared
334 * copy-on-write.)
335 */
336 if (p1->p_limit->p_lflags & PL_SHAREMOD)
337 p2->p_limit = limcopy(p1->p_limit);
338 else {
339 simple_lock(&p1->p_limit->p_slock);
340 p1->p_limit->p_refcnt++;
341 simple_unlock(&p1->p_limit->p_slock);
342 p2->p_limit = p1->p_limit;
343 }
344
345 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
346 p2->p_flag |= P_CONTROLT;
347 if (flags & FORK_PPWAIT)
348 p2->p_flag |= P_PPWAIT;
349 parent = (flags & FORK_NOWAIT) ? initproc : p1;
350 p2->p_pptr = parent;
351 LIST_INIT(&p2->p_children);
352
353 s = proclist_lock_write();
354 LIST_INSERT_AFTER(p1, p2, p_pglist);
355 LIST_INSERT_HEAD(&parent->p_children, p2, p_sibling);
356 proclist_unlock_write(s);
357
358 #ifdef KTRACE
359 /*
360 * Copy traceflag and tracefile if enabled.
361 * If not inherited, these were zeroed above.
362 */
363 if (p1->p_traceflag & KTRFAC_INHERIT) {
364 p2->p_traceflag = p1->p_traceflag;
365 if ((p2->p_tracep = p1->p_tracep) != NULL)
366 ktradref(p2);
367 }
368 #endif
369
370 scheduler_fork_hook(p1, p2);
371
372 /*
373 * Create signal actions for the child process.
374 */
375 sigactsinit(p2, p1, flags & FORK_SHARESIGS);
376
377 /*
378 * p_stats.
379 * Copy parts of p_stats, and zero out the rest.
380 */
381 p2->p_stats = pstatscopy(p1->p_stats);
382
383 /*
384 * If emulation has process fork hook, call it now.
385 */
386 if (p2->p_emul->e_proc_fork)
387 (*p2->p_emul->e_proc_fork)(p2, p1, flags);
388
389 /*
390 * ...and finally, any other random fork hooks that subsystems
391 * might have registered.
392 */
393 doforkhooks(p2, p1);
394
395 /*
396 * This begins the section where we must prevent the parent
397 * from being swapped.
398 */
399 PHOLD(l1);
400
401 uvm_proc_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE);
402
403 /*
404 * Finish creating the child process.
405 * It will return through a different path later.
406 */
407 newlwp(l1, p2, uaddr, inmem, 0, stack, stacksize,
408 (func != NULL) ? func : child_return,
409 arg, &l2);
410
411 /* Now safe for scheduler to see child process */
412 s = proclist_lock_write();
413 p2->p_exitsig = exitsig; /* signal for parent on exit */
414 LIST_INSERT_HEAD(&allproc, p2, p_list);
415 proclist_unlock_write(s);
416
417 #ifdef SYSTRACE
418 /* Tell systrace what's happening. */
419 if (ISSET(p1->p_flag, P_SYSTRACE))
420 systrace_sys_fork(p1, p2);
421 #endif
422
423 #ifdef __HAVE_SYSCALL_INTERN
424 (*p2->p_emul->e_syscall_intern)(p2);
425 #endif
426
427 /*
428 * Make child runnable, set start time, and add to run queue
429 * except if the parent requested the child to start in SSTOP state.
430 */
431 SCHED_LOCK(s);
432 p2->p_stats->p_start = time;
433 p2->p_acflag = AFORK;
434 if (p1->p_flag & P_STOPFORK) {
435 p2->p_nrlwps = 0;
436 p1->p_nstopchild++;
437 p2->p_stat = SSTOP;
438 l2->l_stat = LSSTOP;
439 } else {
440 p2->p_nrlwps = 1;
441 p2->p_stat = SACTIVE;
442 l2->l_stat = LSRUN;
443 setrunqueue(l2);
444 }
445 SCHED_UNLOCK(s);
446
447 /*
448 * Now can be swapped.
449 */
450 PRELE(l1);
451
452 /*
453 * Notify any interested parties about the new process.
454 */
455 KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid);
456
457 /*
458 * Update stats now that we know the fork was successful.
459 */
460 uvmexp.forks++;
461 if (flags & FORK_PPWAIT)
462 uvmexp.forks_ppwait++;
463 if (flags & FORK_SHAREVM)
464 uvmexp.forks_sharevm++;
465
466 /*
467 * Pass a pointer to the new process to the caller.
468 */
469 if (rnewprocp != NULL)
470 *rnewprocp = p2;
471
472 #ifdef KTRACE
473 if (KTRPOINT(p2, KTR_EMUL))
474 p2->p_traceflag |= KTRFAC_TRC_EMUL;
475 #endif
476
477 /*
478 * Preserve synchronization semantics of vfork. If waiting for
479 * child to exec or exit, set P_PPWAIT on child, and sleep on our
480 * proc (in case of exit).
481 */
482 if (flags & FORK_PPWAIT)
483 while (p2->p_flag & P_PPWAIT)
484 tsleep(p1, PWAIT, "ppwait", 0);
485
486 /*
487 * Return child pid to parent process,
488 * marking us as parent via retval[1].
489 */
490 if (retval != NULL) {
491 retval[0] = p2->p_pid;
492 retval[1] = 0;
493 }
494
495 return (0);
496 }
497
498 #if defined(MULTIPROCESSOR)
499 /*
500 * XXX This is a slight hack to get newly-formed processes to
501 * XXX acquire the kernel lock as soon as they run.
502 */
503 void
504 proc_trampoline_mp(void)
505 {
506 struct lwp *l;
507
508 l = curlwp;
509
510 SCHED_ASSERT_UNLOCKED();
511 KERNEL_PROC_LOCK(l);
512 }
513 #endif
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