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 /* 2 * Copyright (c) 1982, 1986, 1989, 1991, 1993 3 * The Regents of the University of California. All rights reserved. 4 * (c) UNIX System Laboratories, Inc. 5 * All or some portions of this file are derived from material licensed 6 * to the University of California by American Telephone and Telegraph 7 * Co. or Unix System Laboratories, Inc. and are reproduced herein with 8 * the permission of UNIX System Laboratories, Inc. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the University of 21 * California, Berkeley and its contributors. 22 * 4. Neither the name of the University nor the names of its contributors 23 * may be used to endorse or promote products derived from this software 24 * without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 * 38 * @(#)kern_fork.c 8.6 (Berkeley) 4/8/94 39 * $FreeBSD: releng/5.1/sys/kern/kern_fork.c 114983 2003-05-13 20:36:02Z jhb $ 40 */ 41 42 #include "opt_ktrace.h" 43 #include "opt_mac.h" 44 45 #include <sys/param.h> 46 #include <sys/systm.h> 47 #include <sys/sysproto.h> 48 #include <sys/eventhandler.h> 49 #include <sys/filedesc.h> 50 #include <sys/kernel.h> 51 #include <sys/sysctl.h> 52 #include <sys/lock.h> 53 #include <sys/malloc.h> 54 #include <sys/mutex.h> 55 #include <sys/proc.h> 56 #include <sys/pioctl.h> 57 #include <sys/resourcevar.h> 58 #include <sys/sched.h> 59 #include <sys/syscall.h> 60 #include <sys/vnode.h> 61 #include <sys/acct.h> 62 #include <sys/mac.h> 63 #include <sys/ktr.h> 64 #include <sys/ktrace.h> 65 #include <sys/kthread.h> 66 #include <sys/unistd.h> 67 #include <sys/jail.h> 68 #include <sys/sx.h> 69 70 #include <vm/vm.h> 71 #include <vm/pmap.h> 72 #include <vm/vm_map.h> 73 #include <vm/vm_extern.h> 74 #include <vm/uma.h> 75 76 #include <sys/vmmeter.h> 77 #include <sys/user.h> 78 #include <machine/critical.h> 79 80 #ifndef _SYS_SYSPROTO_H_ 81 struct fork_args { 82 int dummy; 83 }; 84 #endif 85 86 static int forksleep; /* Place for fork1() to sleep on. */ 87 88 /* 89 * MPSAFE 90 */ 91 /* ARGSUSED */ 92 int 93 fork(td, uap) 94 struct thread *td; 95 struct fork_args *uap; 96 { 97 int error; 98 struct proc *p2; 99 100 error = fork1(td, RFFDG | RFPROC, 0, &p2); 101 if (error == 0) { 102 td->td_retval[0] = p2->p_pid; 103 td->td_retval[1] = 0; 104 } 105 return error; 106 } 107 108 /* 109 * MPSAFE 110 */ 111 /* ARGSUSED */ 112 int 113 vfork(td, uap) 114 struct thread *td; 115 struct vfork_args *uap; 116 { 117 int error; 118 struct proc *p2; 119 120 error = fork1(td, RFFDG | RFPROC | RFPPWAIT | RFMEM, 0, &p2); 121 if (error == 0) { 122 td->td_retval[0] = p2->p_pid; 123 td->td_retval[1] = 0; 124 } 125 return error; 126 } 127 128 /* 129 * MPSAFE 130 */ 131 int 132 rfork(td, uap) 133 struct thread *td; 134 struct rfork_args *uap; 135 { 136 int error; 137 struct proc *p2; 138 139 /* Don't allow kernel only flags. */ 140 if ((uap->flags & RFKERNELONLY) != 0) 141 return (EINVAL); 142 /* 143 * Don't allow sharing of file descriptor table unless 144 * RFTHREAD flag is supplied 145 */ 146 if ((uap->flags & (RFPROC | RFTHREAD | RFFDG | RFCFDG)) == 147 RFPROC) 148 return(EINVAL); 149 error = fork1(td, uap->flags, 0, &p2); 150 if (error == 0) { 151 td->td_retval[0] = p2 ? p2->p_pid : 0; 152 td->td_retval[1] = 0; 153 } 154 return error; 155 } 156 157 158 int nprocs = 1; /* process 0 */ 159 int lastpid = 0; 160 SYSCTL_INT(_kern, OID_AUTO, lastpid, CTLFLAG_RD, &lastpid, 0, 161 "Last used PID"); 162 163 /* 164 * Random component to lastpid generation. We mix in a random factor to make 165 * it a little harder to predict. We sanity check the modulus value to avoid 166 * doing it in critical paths. Don't let it be too small or we pointlessly 167 * waste randomness entropy, and don't let it be impossibly large. Using a 168 * modulus that is too big causes a LOT more process table scans and slows 169 * down fork processing as the pidchecked caching is defeated. 170 */ 171 static int randompid = 0; 172 173 static int 174 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS) 175 { 176 int error, pid; 177 178 sysctl_wire_old_buffer(req, sizeof(int)); 179 sx_xlock(&allproc_lock); 180 pid = randompid; 181 error = sysctl_handle_int(oidp, &pid, 0, req); 182 if (error == 0 && req->newptr != NULL) { 183 if (pid < 0 || pid > PID_MAX - 100) /* out of range */ 184 pid = PID_MAX - 100; 185 else if (pid < 2) /* NOP */ 186 pid = 0; 187 else if (pid < 100) /* Make it reasonable */ 188 pid = 100; 189 randompid = pid; 190 } 191 sx_xunlock(&allproc_lock); 192 return (error); 193 } 194 195 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW, 196 0, 0, sysctl_kern_randompid, "I", "Random PID modulus"); 197 198 int 199 fork1(td, flags, pages, procp) 200 struct thread *td; /* parent proc */ 201 int flags; 202 int pages; 203 struct proc **procp; /* child proc */ 204 { 205 struct proc *p2, *pptr; 206 uid_t uid; 207 struct proc *newproc; 208 int trypid; 209 int ok; 210 static int pidchecked = 0; 211 struct filedesc *fd; 212 struct proc *p1 = td->td_proc; 213 struct thread *td2; 214 struct kse *ke2; 215 struct ksegrp *kg2; 216 struct sigacts *newsigacts; 217 int error; 218 219 /* Can't copy and clear */ 220 if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG)) 221 return (EINVAL); 222 223 mtx_lock(&Giant); 224 /* 225 * Here we don't create a new process, but we divorce 226 * certain parts of a process from itself. 227 */ 228 if ((flags & RFPROC) == 0) { 229 vm_forkproc(td, NULL, NULL, flags); 230 231 /* 232 * Close all file descriptors. 233 */ 234 if (flags & RFCFDG) { 235 struct filedesc *fdtmp; 236 fdtmp = fdinit(td->td_proc->p_fd); 237 fdfree(td); 238 p1->p_fd = fdtmp; 239 } 240 241 /* 242 * Unshare file descriptors (from parent.) 243 */ 244 if (flags & RFFDG) { 245 FILEDESC_LOCK(p1->p_fd); 246 if (p1->p_fd->fd_refcnt > 1) { 247 struct filedesc *newfd; 248 249 newfd = fdcopy(td->td_proc->p_fd); 250 FILEDESC_UNLOCK(p1->p_fd); 251 fdfree(td); 252 p1->p_fd = newfd; 253 } else 254 FILEDESC_UNLOCK(p1->p_fd); 255 } 256 mtx_unlock(&Giant); 257 *procp = NULL; 258 return (0); 259 } 260 261 /* 262 * Note 1:1 allows for forking with one thread coming out on the 263 * other side with the expectation that the process is about to 264 * exec. 265 */ 266 if (p1->p_flag & P_THREADED) { 267 /* 268 * Idle the other threads for a second. 269 * Since the user space is copied, it must remain stable. 270 * In addition, all threads (from the user perspective) 271 * need to either be suspended or in the kernel, 272 * where they will try restart in the parent and will 273 * be aborted in the child. 274 */ 275 PROC_LOCK(p1); 276 if (thread_single(SINGLE_NO_EXIT)) { 277 /* Abort.. someone else is single threading before us */ 278 PROC_UNLOCK(p1); 279 mtx_unlock(&Giant); 280 return (ERESTART); 281 } 282 PROC_UNLOCK(p1); 283 /* 284 * All other activity in this process 285 * is now suspended at the user boundary, 286 * (or other safe places if we think of any). 287 */ 288 } 289 290 /* Allocate new proc. */ 291 newproc = uma_zalloc(proc_zone, M_WAITOK); 292 #ifdef MAC 293 mac_init_proc(newproc); 294 #endif 295 296 /* 297 * Although process entries are dynamically created, we still keep 298 * a global limit on the maximum number we will create. Don't allow 299 * a nonprivileged user to use the last ten processes; don't let root 300 * exceed the limit. The variable nprocs is the current number of 301 * processes, maxproc is the limit. 302 */ 303 sx_xlock(&allproc_lock); 304 uid = td->td_ucred->cr_ruid; 305 if ((nprocs >= maxproc - 10 && uid != 0) || nprocs >= maxproc) { 306 error = EAGAIN; 307 goto fail; 308 } 309 310 /* 311 * Increment the count of procs running with this uid. Don't allow 312 * a nonprivileged user to exceed their current limit. 313 */ 314 PROC_LOCK(p1); 315 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1, 316 (uid != 0) ? p1->p_rlimit[RLIMIT_NPROC].rlim_cur : 0); 317 PROC_UNLOCK(p1); 318 if (!ok) { 319 error = EAGAIN; 320 goto fail; 321 } 322 323 /* 324 * Increment the nprocs resource before blocking can occur. There 325 * are hard-limits as to the number of processes that can run. 326 */ 327 nprocs++; 328 329 /* 330 * Find an unused process ID. We remember a range of unused IDs 331 * ready to use (from lastpid+1 through pidchecked-1). 332 * 333 * If RFHIGHPID is set (used during system boot), do not allocate 334 * low-numbered pids. 335 */ 336 trypid = lastpid + 1; 337 if (flags & RFHIGHPID) { 338 if (trypid < 10) { 339 trypid = 10; 340 } 341 } else { 342 if (randompid) 343 trypid += arc4random() % randompid; 344 } 345 retry: 346 /* 347 * If the process ID prototype has wrapped around, 348 * restart somewhat above 0, as the low-numbered procs 349 * tend to include daemons that don't exit. 350 */ 351 if (trypid >= PID_MAX) { 352 trypid = trypid % PID_MAX; 353 if (trypid < 100) 354 trypid += 100; 355 pidchecked = 0; 356 } 357 if (trypid >= pidchecked) { 358 int doingzomb = 0; 359 360 pidchecked = PID_MAX; 361 /* 362 * Scan the active and zombie procs to check whether this pid 363 * is in use. Remember the lowest pid that's greater 364 * than trypid, so we can avoid checking for a while. 365 */ 366 p2 = LIST_FIRST(&allproc); 367 again: 368 for (; p2 != NULL; p2 = LIST_NEXT(p2, p_list)) { 369 PROC_LOCK(p2); 370 while (p2->p_pid == trypid || 371 p2->p_pgrp->pg_id == trypid || 372 p2->p_session->s_sid == trypid) { 373 trypid++; 374 if (trypid >= pidchecked) { 375 PROC_UNLOCK(p2); 376 goto retry; 377 } 378 } 379 if (p2->p_pid > trypid && pidchecked > p2->p_pid) 380 pidchecked = p2->p_pid; 381 if (p2->p_pgrp->pg_id > trypid && 382 pidchecked > p2->p_pgrp->pg_id) 383 pidchecked = p2->p_pgrp->pg_id; 384 if (p2->p_session->s_sid > trypid && 385 pidchecked > p2->p_session->s_sid) 386 pidchecked = p2->p_session->s_sid; 387 PROC_UNLOCK(p2); 388 } 389 if (!doingzomb) { 390 doingzomb = 1; 391 p2 = LIST_FIRST(&zombproc); 392 goto again; 393 } 394 } 395 396 /* 397 * RFHIGHPID does not mess with the lastpid counter during boot. 398 */ 399 if (flags & RFHIGHPID) 400 pidchecked = 0; 401 else 402 lastpid = trypid; 403 404 p2 = newproc; 405 p2->p_state = PRS_NEW; /* protect against others */ 406 p2->p_pid = trypid; 407 LIST_INSERT_HEAD(&allproc, p2, p_list); 408 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash); 409 sx_xunlock(&allproc_lock); 410 411 /* 412 * Malloc things while we don't hold any locks. 413 */ 414 if (flags & RFSIGSHARE) 415 newsigacts = NULL; 416 else 417 newsigacts = sigacts_alloc(); 418 419 /* 420 * Copy filedesc. 421 */ 422 if (flags & RFCFDG) 423 fd = fdinit(td->td_proc->p_fd); 424 else if (flags & RFFDG) { 425 FILEDESC_LOCK(p1->p_fd); 426 fd = fdcopy(td->td_proc->p_fd); 427 FILEDESC_UNLOCK(p1->p_fd); 428 } else 429 fd = fdshare(p1->p_fd); 430 431 /* 432 * Make a proc table entry for the new process. 433 * Start by zeroing the section of proc that is zero-initialized, 434 * then copy the section that is copied directly from the parent. 435 */ 436 td2 = FIRST_THREAD_IN_PROC(p2); 437 kg2 = FIRST_KSEGRP_IN_PROC(p2); 438 ke2 = FIRST_KSE_IN_KSEGRP(kg2); 439 440 /* Allocate and switch to an alternate kstack if specified */ 441 if (pages != 0) 442 pmap_new_altkstack(td2, pages); 443 444 PROC_LOCK(p2); 445 PROC_LOCK(p1); 446 447 #define RANGEOF(type, start, end) (offsetof(type, end) - offsetof(type, start)) 448 449 bzero(&p2->p_startzero, 450 (unsigned) RANGEOF(struct proc, p_startzero, p_endzero)); 451 bzero(&ke2->ke_startzero, 452 (unsigned) RANGEOF(struct kse, ke_startzero, ke_endzero)); 453 bzero(&td2->td_startzero, 454 (unsigned) RANGEOF(struct thread, td_startzero, td_endzero)); 455 bzero(&kg2->kg_startzero, 456 (unsigned) RANGEOF(struct ksegrp, kg_startzero, kg_endzero)); 457 458 bcopy(&p1->p_startcopy, &p2->p_startcopy, 459 (unsigned) RANGEOF(struct proc, p_startcopy, p_endcopy)); 460 bcopy(&td->td_startcopy, &td2->td_startcopy, 461 (unsigned) RANGEOF(struct thread, td_startcopy, td_endcopy)); 462 bcopy(&td->td_ksegrp->kg_startcopy, &kg2->kg_startcopy, 463 (unsigned) RANGEOF(struct ksegrp, kg_startcopy, kg_endcopy)); 464 #undef RANGEOF 465 466 /* Set up the thread as an active thread (as if runnable). */ 467 ke2->ke_state = KES_THREAD; 468 ke2->ke_thread = td2; 469 td2->td_kse = ke2; 470 471 /* 472 * Duplicate sub-structures as needed. 473 * Increase reference counts on shared objects. 474 * The p_stats substruct is set in vm_forkproc. 475 */ 476 p2->p_flag = 0; 477 if (p1->p_flag & P_PROFIL) 478 startprofclock(p2); 479 mtx_lock_spin(&sched_lock); 480 p2->p_sflag = PS_INMEM; 481 /* 482 * Allow the scheduler to adjust the priority of the child and 483 * parent while we hold the sched_lock. 484 */ 485 sched_fork(p1, p2); 486 487 mtx_unlock_spin(&sched_lock); 488 p2->p_ucred = crhold(td->td_ucred); 489 td2->td_ucred = crhold(p2->p_ucred); /* XXXKSE */ 490 491 pargs_hold(p2->p_args); 492 493 if (flags & RFSIGSHARE) { 494 p2->p_sigacts = sigacts_hold(p1->p_sigacts); 495 } else { 496 sigacts_copy(newsigacts, p1->p_sigacts); 497 p2->p_sigacts = newsigacts; 498 } 499 if (flags & RFLINUXTHPN) 500 p2->p_sigparent = SIGUSR1; 501 else 502 p2->p_sigparent = SIGCHLD; 503 504 /* Bump references to the text vnode (for procfs) */ 505 p2->p_textvp = p1->p_textvp; 506 if (p2->p_textvp) 507 VREF(p2->p_textvp); 508 p2->p_fd = fd; 509 PROC_UNLOCK(p1); 510 PROC_UNLOCK(p2); 511 512 /* 513 * p_limit is copy-on-write, bump refcnt, 514 */ 515 p2->p_limit = p1->p_limit; 516 p2->p_limit->p_refcnt++; 517 518 /* 519 * Setup linkage for kernel based threading 520 */ 521 if((flags & RFTHREAD) != 0) { 522 mtx_lock(&ppeers_lock); 523 p2->p_peers = p1->p_peers; 524 p1->p_peers = p2; 525 p2->p_leader = p1->p_leader; 526 mtx_unlock(&ppeers_lock); 527 PROC_LOCK(p1->p_leader); 528 if ((p1->p_leader->p_flag & P_WEXIT) != 0) { 529 PROC_UNLOCK(p1->p_leader); 530 /* 531 * The task leader is exiting, so process p1 is 532 * going to be killed shortly. Since p1 obviously 533 * isn't dead yet, we know that the leader is either 534 * sending SIGKILL's to all the processes in this 535 * task or is sleeping waiting for all the peers to 536 * exit. We let p1 complete the fork, but we need 537 * to go ahead and kill the new process p2 since 538 * the task leader may not get a chance to send 539 * SIGKILL to it. We leave it on the list so that 540 * the task leader will wait for this new process 541 * to commit suicide. 542 */ 543 PROC_LOCK(p2); 544 psignal(p2, SIGKILL); 545 PROC_UNLOCK(p2); 546 } else 547 PROC_UNLOCK(p1->p_leader); 548 } else { 549 p2->p_peers = NULL; 550 p2->p_leader = p2; 551 } 552 553 sx_xlock(&proctree_lock); 554 PGRP_LOCK(p1->p_pgrp); 555 PROC_LOCK(p2); 556 PROC_LOCK(p1); 557 558 /* 559 * Preserve some more flags in subprocess. P_PROFIL has already 560 * been preserved. 561 */ 562 p2->p_flag |= p1->p_flag & (P_SUGID | P_ALTSTACK); 563 SESS_LOCK(p1->p_session); 564 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 565 p2->p_flag |= P_CONTROLT; 566 SESS_UNLOCK(p1->p_session); 567 if (flags & RFPPWAIT) 568 p2->p_flag |= P_PPWAIT; 569 570 LIST_INSERT_AFTER(p1, p2, p_pglist); 571 PGRP_UNLOCK(p1->p_pgrp); 572 LIST_INIT(&p2->p_children); 573 574 callout_init(&p2->p_itcallout, 1); 575 576 #ifdef KTRACE 577 /* 578 * Copy traceflag and tracefile if enabled. 579 */ 580 mtx_lock(&ktrace_mtx); 581 KASSERT(p2->p_tracevp == NULL, ("new process has a ktrace vnode")); 582 if (p1->p_traceflag & KTRFAC_INHERIT) { 583 p2->p_traceflag = p1->p_traceflag; 584 if ((p2->p_tracevp = p1->p_tracevp) != NULL) { 585 VREF(p2->p_tracevp); 586 KASSERT(p1->p_tracecred != NULL, 587 ("ktrace vnode with no cred")); 588 p2->p_tracecred = crhold(p1->p_tracecred); 589 } 590 } 591 mtx_unlock(&ktrace_mtx); 592 #endif 593 594 /* 595 * If PF_FORK is set, the child process inherits the 596 * procfs ioctl flags from its parent. 597 */ 598 if (p1->p_pfsflags & PF_FORK) { 599 p2->p_stops = p1->p_stops; 600 p2->p_pfsflags = p1->p_pfsflags; 601 } 602 603 /* 604 * This begins the section where we must prevent the parent 605 * from being swapped. 606 */ 607 _PHOLD(p1); 608 PROC_UNLOCK(p1); 609 610 /* 611 * Attach the new process to its parent. 612 * 613 * If RFNOWAIT is set, the newly created process becomes a child 614 * of init. This effectively disassociates the child from the 615 * parent. 616 */ 617 if (flags & RFNOWAIT) 618 pptr = initproc; 619 else 620 pptr = p1; 621 p2->p_pptr = pptr; 622 LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling); 623 sx_xunlock(&proctree_lock); 624 625 /* Inform accounting that we have forked. */ 626 p2->p_acflag = AFORK; 627 PROC_UNLOCK(p2); 628 629 /* 630 * Finish creating the child process. It will return via a different 631 * execution path later. (ie: directly into user mode) 632 */ 633 vm_forkproc(td, p2, td2, flags); 634 635 if (flags == (RFFDG | RFPROC)) { 636 cnt.v_forks++; 637 cnt.v_forkpages += p2->p_vmspace->vm_dsize + 638 p2->p_vmspace->vm_ssize; 639 } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) { 640 cnt.v_vforks++; 641 cnt.v_vforkpages += p2->p_vmspace->vm_dsize + 642 p2->p_vmspace->vm_ssize; 643 } else if (p1 == &proc0) { 644 cnt.v_kthreads++; 645 cnt.v_kthreadpages += p2->p_vmspace->vm_dsize + 646 p2->p_vmspace->vm_ssize; 647 } else { 648 cnt.v_rforks++; 649 cnt.v_rforkpages += p2->p_vmspace->vm_dsize + 650 p2->p_vmspace->vm_ssize; 651 } 652 653 /* 654 * Both processes are set up, now check if any loadable modules want 655 * to adjust anything. 656 * What if they have an error? XXX 657 */ 658 EVENTHANDLER_INVOKE(process_fork, p1, p2, flags); 659 660 /* 661 * If RFSTOPPED not requested, make child runnable and add to 662 * run queue. 663 */ 664 microuptime(&p2->p_stats->p_start); 665 if ((flags & RFSTOPPED) == 0) { 666 mtx_lock_spin(&sched_lock); 667 p2->p_state = PRS_NORMAL; 668 TD_SET_CAN_RUN(td2); 669 setrunqueue(td2); 670 mtx_unlock_spin(&sched_lock); 671 } 672 673 /* 674 * Now can be swapped. 675 */ 676 PROC_LOCK(p1); 677 _PRELE(p1); 678 679 /* 680 * tell any interested parties about the new process 681 */ 682 KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid); 683 PROC_UNLOCK(p1); 684 685 /* 686 * Preserve synchronization semantics of vfork. If waiting for 687 * child to exec or exit, set P_PPWAIT on child, and sleep on our 688 * proc (in case of exit). 689 */ 690 PROC_LOCK(p2); 691 while (p2->p_flag & P_PPWAIT) 692 msleep(p1, &p2->p_mtx, PWAIT, "ppwait", 0); 693 PROC_UNLOCK(p2); 694 695 /* 696 * If other threads are waiting, let them continue now 697 */ 698 if (p1->p_flag & P_THREADED) { 699 PROC_LOCK(p1); 700 thread_single_end(); 701 PROC_UNLOCK(p1); 702 } 703 704 /* 705 * Return child proc pointer to parent. 706 */ 707 mtx_unlock(&Giant); 708 *procp = p2; 709 return (0); 710 fail: 711 sx_xunlock(&allproc_lock); 712 uma_zfree(proc_zone, newproc); 713 if (p1->p_flag & P_THREADED) { 714 PROC_LOCK(p1); 715 thread_single_end(); 716 PROC_UNLOCK(p1); 717 } 718 tsleep(&forksleep, PUSER, "fork", hz / 2); 719 mtx_unlock(&Giant); 720 return (error); 721 } 722 723 /* 724 * Handle the return of a child process from fork1(). This function 725 * is called from the MD fork_trampoline() entry point. 726 */ 727 void 728 fork_exit(callout, arg, frame) 729 void (*callout)(void *, struct trapframe *); 730 void *arg; 731 struct trapframe *frame; 732 { 733 struct thread *td; 734 struct proc *p; 735 736 if ((td = PCPU_GET(deadthread))) { 737 PCPU_SET(deadthread, NULL); 738 thread_stash(td); 739 } 740 td = curthread; 741 p = td->td_proc; 742 td->td_oncpu = PCPU_GET(cpuid); 743 p->p_state = PRS_NORMAL; 744 /* 745 * Finish setting up thread glue. We need to initialize 746 * the thread into a td_critnest=1 state. Some platforms 747 * may have already partially or fully initialized td_critnest 748 * and/or td_md.md_savecrit (when applciable). 749 * 750 * see <arch>/<arch>/critical.c 751 */ 752 sched_lock.mtx_lock = (uintptr_t)td; 753 sched_lock.mtx_recurse = 0; 754 cpu_critical_fork_exit(); 755 CTR3(KTR_PROC, "fork_exit: new thread %p (pid %d, %s)", td, p->p_pid, 756 p->p_comm); 757 if (PCPU_GET(switchtime.sec) == 0) 758 binuptime(PCPU_PTR(switchtime)); 759 PCPU_SET(switchticks, ticks); 760 mtx_unlock_spin(&sched_lock); 761 762 /* 763 * cpu_set_fork_handler intercepts this function call to 764 * have this call a non-return function to stay in kernel mode. 765 * initproc has its own fork handler, but it does return. 766 */ 767 KASSERT(callout != NULL, ("NULL callout in fork_exit")); 768 callout(arg, frame); 769 770 /* 771 * Check if a kernel thread misbehaved and returned from its main 772 * function. 773 */ 774 PROC_LOCK(p); 775 if (p->p_flag & P_KTHREAD) { 776 PROC_UNLOCK(p); 777 mtx_lock(&Giant); 778 printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n", 779 p->p_comm, p->p_pid); 780 kthread_exit(0); 781 } 782 PROC_UNLOCK(p); 783 #ifdef DIAGNOSTIC 784 cred_free_thread(td); 785 #endif 786 mtx_assert(&Giant, MA_NOTOWNED); 787 } 788 789 /* 790 * Simplified back end of syscall(), used when returning from fork() 791 * directly into user mode. Giant is not held on entry, and must not 792 * be held on return. This function is passed in to fork_exit() as the 793 * first parameter and is called when returning to a new userland process. 794 */ 795 void 796 fork_return(td, frame) 797 struct thread *td; 798 struct trapframe *frame; 799 { 800 801 userret(td, frame, 0); 802 #ifdef KTRACE 803 if (KTRPOINT(td, KTR_SYSRET)) 804 ktrsysret(SYS_fork, 0, 0); 805 #endif 806 mtx_assert(&Giant, MA_NOTOWNED); 807 }
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