Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_fork.c
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1 /* $NetBSD: kern_fork.c,v 1.171 2008/10/11 13:40:57 pooka Exp $ */ 2 3 /*- 4 * Copyright (c) 1999, 2001, 2004, 2006, 2007, 2008 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, by Charles M. Hannum, and by Andrew Doran. 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 21 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 22 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 23 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 24 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 25 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 26 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 27 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 28 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 29 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 30 * POSSIBILITY OF SUCH DAMAGE. 31 */ 32 33 /* 34 * Copyright (c) 1982, 1986, 1989, 1991, 1993 35 * The Regents of the University of California. All rights reserved. 36 * (c) UNIX System Laboratories, Inc. 37 * All or some portions of this file are derived from material licensed 38 * to the University of California by American Telephone and Telegraph 39 * Co. or Unix System Laboratories, Inc. and are reproduced herein with 40 * the permission of UNIX System Laboratories, Inc. 41 * 42 * Redistribution and use in source and binary forms, with or without 43 * modification, are permitted provided that the following conditions 44 * are met: 45 * 1. Redistributions of source code must retain the above copyright 46 * notice, this list of conditions and the following disclaimer. 47 * 2. Redistributions in binary form must reproduce the above copyright 48 * notice, this list of conditions and the following disclaimer in the 49 * documentation and/or other materials provided with the distribution. 50 * 3. Neither the name of the University nor the names of its contributors 51 * may be used to endorse or promote products derived from this software 52 * without specific prior written permission. 53 * 54 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 55 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 56 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 57 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 58 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 59 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 60 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 61 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 62 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 63 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 64 * SUCH DAMAGE. 65 * 66 * @(#)kern_fork.c 8.8 (Berkeley) 2/14/95 67 */ 68 69 #include <sys/cdefs.h> 70 __KERNEL_RCSID(0, "$NetBSD: kern_fork.c,v 1.171 2008/10/11 13:40:57 pooka Exp $"); 71 72 #include "opt_ktrace.h" 73 74 #include <sys/param.h> 75 #include <sys/systm.h> 76 #include <sys/filedesc.h> 77 #include <sys/kernel.h> 78 #include <sys/malloc.h> 79 #include <sys/pool.h> 80 #include <sys/mount.h> 81 #include <sys/proc.h> 82 #include <sys/ras.h> 83 #include <sys/resourcevar.h> 84 #include <sys/vnode.h> 85 #include <sys/file.h> 86 #include <sys/acct.h> 87 #include <sys/ktrace.h> 88 #include <sys/vmmeter.h> 89 #include <sys/sched.h> 90 #include <sys/signalvar.h> 91 #include <sys/kauth.h> 92 #include <sys/atomic.h> 93 #include <sys/syscallargs.h> 94 #include <sys/uidinfo.h> 95 96 #include <uvm/uvm_extern.h> 97 98 u_int nprocs = 1; /* process 0 */ 99 100 /* 101 * Number of ticks to sleep if fork() would fail due to process hitting 102 * limits. Exported in miliseconds to userland via sysctl. 103 */ 104 int forkfsleep = 0; 105 106 /*ARGSUSED*/ 107 int 108 sys_fork(struct lwp *l, const void *v, register_t *retval) 109 { 110 111 return (fork1(l, 0, SIGCHLD, NULL, 0, NULL, NULL, retval, NULL)); 112 } 113 114 /* 115 * vfork(2) system call compatible with 4.4BSD (i.e. BSD with Mach VM). 116 * Address space is not shared, but parent is blocked until child exit. 117 */ 118 /*ARGSUSED*/ 119 int 120 sys_vfork(struct lwp *l, const void *v, register_t *retval) 121 { 122 123 return (fork1(l, FORK_PPWAIT, SIGCHLD, NULL, 0, NULL, NULL, 124 retval, NULL)); 125 } 126 127 /* 128 * New vfork(2) system call for NetBSD, which implements original 3BSD vfork(2) 129 * semantics. Address space is shared, and parent is blocked until child exit. 130 */ 131 /*ARGSUSED*/ 132 int 133 sys___vfork14(struct lwp *l, const void *v, register_t *retval) 134 { 135 136 return (fork1(l, FORK_PPWAIT|FORK_SHAREVM, SIGCHLD, NULL, 0, 137 NULL, NULL, retval, NULL)); 138 } 139 140 /* 141 * Linux-compatible __clone(2) system call. 142 */ 143 int 144 sys___clone(struct lwp *l, const struct sys___clone_args *uap, register_t *retval) 145 { 146 /* { 147 syscallarg(int) flags; 148 syscallarg(void *) stack; 149 } */ 150 int flags, sig; 151 152 /* 153 * We don't support the CLONE_PID or CLONE_PTRACE flags. 154 */ 155 if (SCARG(uap, flags) & (CLONE_PID|CLONE_PTRACE)) 156 return (EINVAL); 157 158 /* 159 * Linux enforces CLONE_VM with CLONE_SIGHAND, do same. 160 */ 161 if (SCARG(uap, flags) & CLONE_SIGHAND 162 && (SCARG(uap, flags) & CLONE_VM) == 0) 163 return (EINVAL); 164 165 flags = 0; 166 167 if (SCARG(uap, flags) & CLONE_VM) 168 flags |= FORK_SHAREVM; 169 if (SCARG(uap, flags) & CLONE_FS) 170 flags |= FORK_SHARECWD; 171 if (SCARG(uap, flags) & CLONE_FILES) 172 flags |= FORK_SHAREFILES; 173 if (SCARG(uap, flags) & CLONE_SIGHAND) 174 flags |= FORK_SHARESIGS; 175 if (SCARG(uap, flags) & CLONE_VFORK) 176 flags |= FORK_PPWAIT; 177 178 sig = SCARG(uap, flags) & CLONE_CSIGNAL; 179 if (sig < 0 || sig >= _NSIG) 180 return (EINVAL); 181 182 /* 183 * Note that the Linux API does not provide a portable way of 184 * specifying the stack area; the caller must know if the stack 185 * grows up or down. So, we pass a stack size of 0, so that the 186 * code that makes this adjustment is a noop. 187 */ 188 return (fork1(l, flags, sig, SCARG(uap, stack), 0, 189 NULL, NULL, retval, NULL)); 190 } 191 192 /* print the 'table full' message once per 10 seconds */ 193 struct timeval fork_tfmrate = { 10, 0 }; 194 195 /* 196 * General fork call. Note that another LWP in the process may call exec() 197 * or exit() while we are forking. It's safe to continue here, because 198 * neither operation will complete until all LWPs have exited the process. 199 */ 200 int 201 fork1(struct lwp *l1, int flags, int exitsig, void *stack, size_t stacksize, 202 void (*func)(void *), void *arg, register_t *retval, 203 struct proc **rnewprocp) 204 { 205 struct proc *p1, *p2, *parent; 206 struct plimit *p1_lim; 207 uid_t uid; 208 struct lwp *l2; 209 int count; 210 vaddr_t uaddr; 211 bool inmem; 212 int tmp; 213 int tnprocs; 214 int error = 0; 215 216 p1 = l1->l_proc; 217 uid = kauth_cred_getuid(l1->l_cred); 218 tnprocs = atomic_inc_uint_nv(&nprocs); 219 220 /* 221 * Although process entries are dynamically created, we still keep 222 * a global limit on the maximum number we will create. 223 */ 224 if (__predict_false(tnprocs >= maxproc)) 225 error = -1; 226 else 227 error = kauth_authorize_process(l1->l_cred, 228 KAUTH_PROCESS_FORK, p1, KAUTH_ARG(tnprocs), NULL, NULL); 229 230 if (error) { 231 static struct timeval lasttfm; 232 atomic_dec_uint(&nprocs); 233 if (ratecheck(&lasttfm, &fork_tfmrate)) 234 tablefull("proc", "increase kern.maxproc or NPROC"); 235 if (forkfsleep) 236 kpause("forkmx", false, forkfsleep, NULL); 237 return (EAGAIN); 238 } 239 240 /* 241 * Enforce limits. 242 */ 243 count = chgproccnt(uid, 1); 244 if (uid != 0 && 245 __predict_false(count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur)) { 246 (void)chgproccnt(uid, -1); 247 atomic_dec_uint(&nprocs); 248 if (forkfsleep) 249 kpause("forkulim", false, forkfsleep, NULL); 250 return (EAGAIN); 251 } 252 253 /* 254 * Allocate virtual address space for the U-area now, while it 255 * is still easy to abort the fork operation if we're out of 256 * kernel virtual address space. The actual U-area pages will 257 * be allocated and wired in uvm_fork() if needed. 258 */ 259 260 inmem = uvm_uarea_alloc(&uaddr); 261 if (__predict_false(uaddr == 0)) { 262 (void)chgproccnt(uid, -1); 263 atomic_dec_uint(&nprocs); 264 return (ENOMEM); 265 } 266 267 /* 268 * We are now committed to the fork. From here on, we may 269 * block on resources, but resource allocation may NOT fail. 270 */ 271 272 /* Allocate new proc. */ 273 p2 = proc_alloc(); 274 275 /* 276 * Make a proc table entry for the new process. 277 * Start by zeroing the section of proc that is zero-initialized, 278 * then copy the section that is copied directly from the parent. 279 */ 280 memset(&p2->p_startzero, 0, 281 (unsigned) ((char *)&p2->p_endzero - (char *)&p2->p_startzero)); 282 memcpy(&p2->p_startcopy, &p1->p_startcopy, 283 (unsigned) ((char *)&p2->p_endcopy - (char *)&p2->p_startcopy)); 284 285 CIRCLEQ_INIT(&p2->p_sigpend.sp_info); 286 287 LIST_INIT(&p2->p_lwps); 288 LIST_INIT(&p2->p_sigwaiters); 289 290 /* 291 * Duplicate sub-structures as needed. 292 * Increase reference counts on shared objects. 293 * The p_stats and p_sigacts substructs are set in uvm_fork(). 294 * Inherit flags we want to keep. The flags related to SIGCHLD 295 * handling are important in order to keep a consistent behaviour 296 * for the child after the fork. 297 */ 298 p2->p_flag = p1->p_flag & (PK_SUGID | PK_NOCLDWAIT | PK_CLDSIGIGN); 299 p2->p_emul = p1->p_emul; 300 p2->p_execsw = p1->p_execsw; 301 302 if (flags & FORK_SYSTEM) { 303 /* 304 * Mark it as a system process. Set P_NOCLDWAIT so that 305 * children are reparented to init(8) when they exit. 306 * init(8) can easily wait them out for us. 307 */ 308 p2->p_flag |= (PK_SYSTEM | PK_NOCLDWAIT); 309 } 310 311 mutex_init(&p2->p_stmutex, MUTEX_DEFAULT, IPL_HIGH); 312 mutex_init(&p2->p_auxlock, MUTEX_DEFAULT, IPL_NONE); 313 rw_init(&p2->p_reflock); 314 cv_init(&p2->p_waitcv, "wait"); 315 cv_init(&p2->p_lwpcv, "lwpwait"); 316 317 /* 318 * Share a lock between the processes if they are to share signal 319 * state: we must synchronize access to it. 320 */ 321 if (flags & FORK_SHARESIGS) { 322 p2->p_lock = p1->p_lock; 323 mutex_obj_hold(p1->p_lock); 324 } else 325 p2->p_lock = mutex_obj_alloc(MUTEX_DEFAULT, IPL_NONE); 326 327 kauth_proc_fork(p1, p2); 328 329 p2->p_raslist = NULL; 330 #if defined(__HAVE_RAS) 331 ras_fork(p1, p2); 332 #endif 333 334 /* bump references to the text vnode (for procfs) */ 335 p2->p_textvp = p1->p_textvp; 336 if (p2->p_textvp) 337 VREF(p2->p_textvp); 338 339 if (flags & FORK_SHAREFILES) 340 fd_share(p2); 341 else if (flags & FORK_CLEANFILES) 342 p2->p_fd = fd_init(NULL); 343 else 344 p2->p_fd = fd_copy(); 345 346 if (flags & FORK_SHARECWD) 347 cwdshare(p2); 348 else 349 p2->p_cwdi = cwdinit(); 350 351 /* 352 * p_limit (rlimit stuff) is usually copy-on-write, so we just need 353 * to bump pl_refcnt. 354 * However in some cases (see compat irix, and plausibly from clone) 355 * the parent and child share limits - in which case nothing else 356 * must have a copy of the limits (PL_SHAREMOD is set). 357 */ 358 if (__predict_false(flags & FORK_SHARELIMIT)) 359 lim_privatise(p1, 1); 360 p1_lim = p1->p_limit; 361 if (p1_lim->pl_flags & PL_WRITEABLE && !(flags & FORK_SHARELIMIT)) 362 p2->p_limit = lim_copy(p1_lim); 363 else { 364 lim_addref(p1_lim); 365 p2->p_limit = p1_lim; 366 } 367 368 p2->p_lflag = ((flags & FORK_PPWAIT) ? PL_PPWAIT : 0); 369 p2->p_sflag = 0; 370 p2->p_slflag = 0; 371 parent = (flags & FORK_NOWAIT) ? initproc : p1; 372 p2->p_pptr = parent; 373 p2->p_ppid = parent->p_pid; 374 LIST_INIT(&p2->p_children); 375 376 p2->p_aio = NULL; 377 378 #ifdef KTRACE 379 /* 380 * Copy traceflag and tracefile if enabled. 381 * If not inherited, these were zeroed above. 382 */ 383 if (p1->p_traceflag & KTRFAC_INHERIT) { 384 mutex_enter(&ktrace_lock); 385 p2->p_traceflag = p1->p_traceflag; 386 if ((p2->p_tracep = p1->p_tracep) != NULL) 387 ktradref(p2); 388 mutex_exit(&ktrace_lock); 389 } 390 #endif 391 392 /* 393 * Create signal actions for the child process. 394 */ 395 p2->p_sigacts = sigactsinit(p1, flags & FORK_SHARESIGS); 396 mutex_enter(p1->p_lock); 397 p2->p_sflag |= 398 (p1->p_sflag & (PS_STOPFORK | PS_STOPEXEC | PS_NOCLDSTOP)); 399 sched_proc_fork(p1, p2); 400 mutex_exit(p1->p_lock); 401 402 p2->p_stflag = p1->p_stflag; 403 404 /* 405 * p_stats. 406 * Copy parts of p_stats, and zero out the rest. 407 */ 408 p2->p_stats = pstatscopy(p1->p_stats); 409 410 /* 411 * If emulation has process fork hook, call it now. 412 */ 413 if (p2->p_emul->e_proc_fork) 414 (*p2->p_emul->e_proc_fork)(p2, p1, flags); 415 416 /* 417 * ...and finally, any other random fork hooks that subsystems 418 * might have registered. 419 */ 420 doforkhooks(p2, p1); 421 422 /* 423 * This begins the section where we must prevent the parent 424 * from being swapped. 425 */ 426 uvm_lwp_hold(l1); 427 uvm_proc_fork(p1, p2, (flags & FORK_SHAREVM) ? true : false); 428 429 /* 430 * Finish creating the child process. 431 * It will return through a different path later. 432 */ 433 lwp_create(l1, p2, uaddr, inmem, (flags & FORK_PPWAIT) ? LWP_VFORK : 0, 434 stack, stacksize, (func != NULL) ? func : child_return, arg, &l2, 435 l1->l_class); 436 437 /* 438 * It's now safe for the scheduler and other processes to see the 439 * child process. 440 */ 441 mutex_enter(proc_lock); 442 443 if (p1->p_session->s_ttyvp != NULL && p1->p_lflag & PL_CONTROLT) 444 p2->p_lflag |= PL_CONTROLT; 445 446 LIST_INSERT_HEAD(&parent->p_children, p2, p_sibling); 447 p2->p_exitsig = exitsig; /* signal for parent on exit */ 448 449 LIST_INSERT_AFTER(p1, p2, p_pglist); 450 LIST_INSERT_HEAD(&allproc, p2, p_list); 451 452 p2->p_trace_enabled = trace_is_enabled(p2); 453 #ifdef __HAVE_SYSCALL_INTERN 454 (*p2->p_emul->e_syscall_intern)(p2); 455 #endif 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 if (ktrpoint(KTR_EMUL)) 473 p2->p_traceflag |= KTRFAC_TRC_EMUL; 474 475 /* 476 * Now can be swapped. 477 */ 478 uvm_lwp_rele(l1); 479 480 /* 481 * Notify any interested parties about the new process. 482 */ 483 if (!SLIST_EMPTY(&p1->p_klist)) { 484 mutex_exit(proc_lock); 485 KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid); 486 mutex_enter(proc_lock); 487 } 488 489 /* 490 * Make child runnable, set start time, and add to run queue except 491 * if the parent requested the child to start in SSTOP state. 492 */ 493 tmp = (p2->p_userret != NULL ? LW_WUSERRET : 0); 494 mutex_enter(p2->p_lock); 495 496 /* 497 * Start profiling. 498 */ 499 if ((p2->p_stflag & PST_PROFIL) != 0) { 500 mutex_spin_enter(&p2->p_stmutex); 501 startprofclock(p2); 502 mutex_spin_exit(&p2->p_stmutex); 503 } 504 505 getmicrotime(&p2->p_stats->p_start); 506 p2->p_acflag = AFORK; 507 lwp_lock(l2); 508 if (p2->p_sflag & PS_STOPFORK) { 509 p2->p_nrlwps = 0; 510 p2->p_stat = SSTOP; 511 p2->p_waited = 0; 512 p1->p_nstopchild++; 513 l2->l_stat = LSSTOP; 514 l2->l_flag |= tmp; 515 lwp_unlock(l2); 516 } else { 517 p2->p_nrlwps = 1; 518 p2->p_stat = SACTIVE; 519 l2->l_stat = LSRUN; 520 l2->l_flag |= tmp; 521 sched_enqueue(l2, false); 522 lwp_unlock(l2); 523 } 524 525 mutex_exit(p2->p_lock); 526 527 /* 528 * Preserve synchronization semantics of vfork. If waiting for 529 * child to exec or exit, set PL_PPWAIT on child, and sleep on our 530 * proc (in case of exit). 531 */ 532 while (p2->p_lflag & PL_PPWAIT) 533 cv_wait(&p1->p_waitcv, proc_lock); 534 535 mutex_exit(proc_lock); 536 537 /* 538 * Return child pid to parent process, 539 * marking us as parent via retval[1]. 540 */ 541 if (retval != NULL) { 542 retval[0] = p2->p_pid; 543 retval[1] = 0; 544 } 545 546 return (0); 547 }
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