FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_fork.c
1 /* $NetBSD: kern_fork.c,v 1.128 2006/11/01 10:17:58 yamt 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 1.128 2006/11/01 10:17:58 yamt 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 #include <sys/kauth.h>
104
105 #include <sys/sa.h>
106 #include <sys/syscallargs.h>
107
108 #include <uvm/uvm_extern.h>
109
110
111 int nprocs = 1; /* process 0 */
112
113 /*
114 * Number of ticks to sleep if fork() would fail due to process hitting
115 * limits. Exported in miliseconds to userland via sysctl.
116 */
117 int forkfsleep = 0;
118
119 /*ARGSUSED*/
120 int
121 sys_fork(struct lwp *l, void *v, register_t *retval)
122 {
123
124 return (fork1(l, 0, SIGCHLD, NULL, 0, NULL, NULL, retval, NULL));
125 }
126
127 /*
128 * vfork(2) system call compatible with 4.4BSD (i.e. BSD with Mach VM).
129 * Address space is not shared, but parent is blocked until child exit.
130 */
131 /*ARGSUSED*/
132 int
133 sys_vfork(struct lwp *l, void *v, register_t *retval)
134 {
135
136 return (fork1(l, FORK_PPWAIT, SIGCHLD, NULL, 0, NULL, NULL,
137 retval, NULL));
138 }
139
140 /*
141 * New vfork(2) system call for NetBSD, which implements original 3BSD vfork(2)
142 * semantics. Address space is shared, and parent is blocked until child exit.
143 */
144 /*ARGSUSED*/
145 int
146 sys___vfork14(struct lwp *l, void *v, register_t *retval)
147 {
148
149 return (fork1(l, FORK_PPWAIT|FORK_SHAREVM, SIGCHLD, NULL, 0,
150 NULL, NULL, retval, NULL));
151 }
152
153 /*
154 * Linux-compatible __clone(2) system call.
155 */
156 int
157 sys___clone(struct lwp *l, void *v, register_t *retval)
158 {
159 struct sys___clone_args /* {
160 syscallarg(int) flags;
161 syscallarg(void *) stack;
162 } */ *uap = v;
163 int flags, sig;
164
165 /*
166 * We don't support the CLONE_PID or CLONE_PTRACE flags.
167 */
168 if (SCARG(uap, flags) & (CLONE_PID|CLONE_PTRACE))
169 return (EINVAL);
170
171 /*
172 * Linux enforces CLONE_VM with CLONE_SIGHAND, do same.
173 */
174 if (SCARG(uap, flags) & CLONE_SIGHAND
175 && (SCARG(uap, flags) & CLONE_VM) == 0)
176 return (EINVAL);
177
178 flags = 0;
179
180 if (SCARG(uap, flags) & CLONE_VM)
181 flags |= FORK_SHAREVM;
182 if (SCARG(uap, flags) & CLONE_FS)
183 flags |= FORK_SHARECWD;
184 if (SCARG(uap, flags) & CLONE_FILES)
185 flags |= FORK_SHAREFILES;
186 if (SCARG(uap, flags) & CLONE_SIGHAND)
187 flags |= FORK_SHARESIGS;
188 if (SCARG(uap, flags) & CLONE_VFORK)
189 flags |= FORK_PPWAIT;
190
191 sig = SCARG(uap, flags) & CLONE_CSIGNAL;
192 if (sig < 0 || sig >= _NSIG)
193 return (EINVAL);
194
195 /*
196 * Note that the Linux API does not provide a portable way of
197 * specifying the stack area; the caller must know if the stack
198 * grows up or down. So, we pass a stack size of 0, so that the
199 * code that makes this adjustment is a noop.
200 */
201 return (fork1(l, flags, sig, SCARG(uap, stack), 0,
202 NULL, NULL, retval, NULL));
203 }
204
205 /* print the 'table full' message once per 10 seconds */
206 struct timeval fork_tfmrate = { 10, 0 };
207
208 int
209 fork1(struct lwp *l1, int flags, int exitsig, void *stack, size_t stacksize,
210 void (*func)(void *), void *arg, register_t *retval,
211 struct proc **rnewprocp)
212 {
213 struct proc *p1, *p2, *parent;
214 uid_t uid;
215 struct lwp *l2;
216 int count, s;
217 vaddr_t uaddr;
218 boolean_t inmem;
219
220 /*
221 * Although process entries are dynamically created, we still keep
222 * a global limit on the maximum number we will create. Don't allow
223 * a nonprivileged user to use the last few processes; don't let root
224 * exceed the limit. The variable nprocs is the current number of
225 * processes, maxproc is the limit.
226 */
227 p1 = l1->l_proc;
228 uid = kauth_cred_getuid(p1->p_cred);
229 if (__predict_false((nprocs >= maxproc - 5 && uid != 0) ||
230 nprocs >= maxproc)) {
231 static struct timeval lasttfm;
232
233 if (ratecheck(&lasttfm, &fork_tfmrate))
234 tablefull("proc", "increase kern.maxproc or NPROC");
235 if (forkfsleep)
236 (void)tsleep(&nprocs, PUSER, "forkmx", forkfsleep);
237 return (EAGAIN);
238 }
239 nprocs++;
240
241 /*
242 * Increment the count of procs running with this uid. Don't allow
243 * a nonprivileged user to exceed their current limit.
244 */
245 count = chgproccnt(uid, 1);
246 if (__predict_false(uid != 0 && count >
247 p1->p_rlimit[RLIMIT_NPROC].rlim_cur)) {
248 (void)chgproccnt(uid, -1);
249 nprocs--;
250 if (forkfsleep)
251 (void)tsleep(&nprocs, PUSER, "forkulim", forkfsleep);
252 return (EAGAIN);
253 }
254
255 /*
256 * Allocate virtual address space for the U-area now, while it
257 * is still easy to abort the fork operation if we're out of
258 * kernel virtual address space. The actual U-area pages will
259 * be allocated and wired in uvm_fork() if needed.
260 */
261
262 inmem = uvm_uarea_alloc(&uaddr);
263 if (__predict_false(uaddr == 0)) {
264 (void)chgproccnt(uid, -1);
265 nprocs--;
266 return (ENOMEM);
267 }
268
269 /*
270 * We are now committed to the fork. From here on, we may
271 * block on resources, but resource allocation may NOT fail.
272 */
273
274 /* Allocate new proc. */
275 p2 = proc_alloc();
276
277 /*
278 * Make a proc table entry for the new process.
279 * Start by zeroing the section of proc that is zero-initialized,
280 * then copy the section that is copied directly from the parent.
281 */
282 memset(&p2->p_startzero, 0,
283 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero));
284 memcpy(&p2->p_startcopy, &p1->p_startcopy,
285 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy));
286
287 simple_lock_init(&p2->p_sigctx.ps_silock);
288 CIRCLEQ_INIT(&p2->p_sigctx.ps_siginfo);
289 simple_lock_init(&p2->p_lock);
290 LIST_INIT(&p2->p_lwps);
291
292 /*
293 * Duplicate sub-structures as needed.
294 * Increase reference counts on shared objects.
295 * The p_stats and p_sigacts substructs are set in uvm_fork().
296 * Inherit flags we want to keep. The flags related to SIGCHLD
297 * handling are important in order to keep a consistent behaviour
298 * for the child after the fork.
299 */
300 p2->p_flag = p1->p_flag & (P_SUGID | P_STOPFORK | P_STOPEXEC |
301 P_NOCLDSTOP | P_NOCLDWAIT | P_CLDSIGIGN);
302 p2->p_emul = p1->p_emul;
303 p2->p_execsw = p1->p_execsw;
304
305 if (p1->p_flag & P_PROFIL)
306 startprofclock(p2);
307
308 kauth_cred_hold(p1->p_cred);
309 p2->p_cred = p1->p_cred;
310
311 LIST_INIT(&p2->p_raslist);
312 #if defined(__HAVE_RAS)
313 ras_fork(p1, p2);
314 #endif
315
316 /* bump references to the text vnode (for procfs) */
317 p2->p_textvp = p1->p_textvp;
318 if (p2->p_textvp)
319 VREF(p2->p_textvp);
320
321 if (flags & FORK_SHAREFILES)
322 fdshare(p1, p2);
323 else if (flags & FORK_CLEANFILES)
324 p2->p_fd = fdinit(p1);
325 else
326 p2->p_fd = fdcopy(p1);
327
328 if (flags & FORK_SHARECWD)
329 cwdshare(p1, p2);
330 else
331 p2->p_cwdi = cwdinit(p1);
332
333 /*
334 * If p_limit is still copy-on-write, bump refcnt,
335 * otherwise get a copy that won't be modified.
336 * (If PL_SHAREMOD is clear, the structure is shared
337 * copy-on-write.)
338 */
339 if (p1->p_limit->p_lflags & PL_SHAREMOD)
340 p2->p_limit = limcopy(p1->p_limit);
341 else {
342 simple_lock(&p1->p_limit->p_slock);
343 p1->p_limit->p_refcnt++;
344 simple_unlock(&p1->p_limit->p_slock);
345 p2->p_limit = p1->p_limit;
346 }
347
348 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
349 p2->p_flag |= P_CONTROLT;
350 if (flags & FORK_PPWAIT)
351 p2->p_flag |= P_PPWAIT;
352 parent = (flags & FORK_NOWAIT) ? initproc : p1;
353 p2->p_pptr = parent;
354 LIST_INIT(&p2->p_children);
355
356 s = proclist_lock_write();
357 LIST_INSERT_AFTER(p1, p2, p_pglist);
358 LIST_INSERT_HEAD(&parent->p_children, p2, p_sibling);
359 proclist_unlock_write(s);
360
361 #ifdef KTRACE
362 /*
363 * Copy traceflag and tracefile if enabled.
364 * If not inherited, these were zeroed above.
365 */
366 if (p1->p_traceflag & KTRFAC_INHERIT) {
367 p2->p_traceflag = p1->p_traceflag;
368 if ((p2->p_tracep = p1->p_tracep) != NULL)
369 ktradref(p2);
370 }
371 #endif
372
373 scheduler_fork_hook(p1, p2);
374
375 /*
376 * Create signal actions for the child process.
377 */
378 sigactsinit(p2, p1, flags & FORK_SHARESIGS);
379
380 /*
381 * p_stats.
382 * Copy parts of p_stats, and zero out the rest.
383 */
384 p2->p_stats = pstatscopy(p1->p_stats);
385
386 /*
387 * If emulation has process fork hook, call it now.
388 */
389 if (p2->p_emul->e_proc_fork)
390 (*p2->p_emul->e_proc_fork)(p2, p1, flags);
391
392 /*
393 * ...and finally, any other random fork hooks that subsystems
394 * might have registered.
395 */
396 doforkhooks(p2, p1);
397
398 /*
399 * This begins the section where we must prevent the parent
400 * from being swapped.
401 */
402 PHOLD(l1);
403
404 uvm_proc_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE);
405
406 /*
407 * Finish creating the child process.
408 * It will return through a different path later.
409 */
410 newlwp(l1, p2, uaddr, inmem, 0, stack, stacksize,
411 (func != NULL) ? func : child_return,
412 arg, &l2);
413
414 /* Now safe for scheduler to see child process */
415 s = proclist_lock_write();
416 p2->p_exitsig = exitsig; /* signal for parent on exit */
417 LIST_INSERT_HEAD(&allproc, p2, p_list);
418 proclist_unlock_write(s);
419
420 #ifdef SYSTRACE
421 /* Tell systrace what's happening. */
422 if (ISSET(p1->p_flag, P_SYSTRACE))
423 systrace_sys_fork(p1, p2);
424 #endif
425
426 #ifdef __HAVE_SYSCALL_INTERN
427 (*p2->p_emul->e_syscall_intern)(p2);
428 #endif
429
430 /*
431 * Make child runnable, set start time, and add to run queue
432 * except if the parent requested the child to start in SSTOP state.
433 */
434 SCHED_LOCK(s);
435 getmicrotime(&p2->p_stats->p_start);
436 p2->p_acflag = AFORK;
437 if (p1->p_flag & P_STOPFORK) {
438 p2->p_nrlwps = 0;
439 p1->p_nstopchild++;
440 p2->p_stat = SSTOP;
441 l2->l_stat = LSSTOP;
442 } else {
443 p2->p_nrlwps = 1;
444 p2->p_stat = SACTIVE;
445 l2->l_stat = LSRUN;
446 setrunqueue(l2);
447 }
448 SCHED_UNLOCK(s);
449
450 /*
451 * Now can be swapped.
452 */
453 PRELE(l1);
454
455 /*
456 * Notify any interested parties about the new process.
457 */
458 KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid);
459
460 /*
461 * Update stats now that we know the fork was successful.
462 */
463 uvmexp.forks++;
464 if (flags & FORK_PPWAIT)
465 uvmexp.forks_ppwait++;
466 if (flags & FORK_SHAREVM)
467 uvmexp.forks_sharevm++;
468
469 /*
470 * Pass a pointer to the new process to the caller.
471 */
472 if (rnewprocp != NULL)
473 *rnewprocp = p2;
474
475 #ifdef KTRACE
476 if (KTRPOINT(p2, KTR_EMUL))
477 p2->p_traceflag |= KTRFAC_TRC_EMUL;
478 #endif
479
480 /*
481 * Preserve synchronization semantics of vfork. If waiting for
482 * child to exec or exit, set P_PPWAIT on child, and sleep on our
483 * proc (in case of exit).
484 */
485 if (flags & FORK_PPWAIT)
486 while (p2->p_flag & P_PPWAIT)
487 tsleep(p1, PWAIT, "ppwait", 0);
488
489 /*
490 * Return child pid to parent process,
491 * marking us as parent via retval[1].
492 */
493 if (retval != NULL) {
494 retval[0] = p2->p_pid;
495 retval[1] = 0;
496 }
497
498 return (0);
499 }
500
501 #if defined(MULTIPROCESSOR)
502 /*
503 * XXX This is a slight hack to get newly-formed processes to
504 * XXX acquire the kernel lock as soon as they run.
505 */
506 void
507 proc_trampoline_mp(void)
508 {
509 struct lwp *l;
510
511 l = curlwp;
512
513 SCHED_ASSERT_UNLOCKED();
514 KERNEL_PROC_LOCK(l);
515 }
516 #endif
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