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: 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 1.76 2008/05/09 06:38:19 dillon Exp $ 41 */ 42 43 #include "opt_ktrace.h" 44 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> 52 #include <sys/proc.h> 53 #include <sys/resourcevar.h> 54 #include <sys/vnode.h> 55 #include <sys/acct.h> 56 #include <sys/ktrace.h> 57 #include <sys/unistd.h> 58 #include <sys/jail.h> 59 #include <sys/caps.h> 60 61 #include <vm/vm.h> 62 #include <sys/lock.h> 63 #include <vm/pmap.h> 64 #include <vm/vm_map.h> 65 #include <vm/vm_extern.h> 66 #include <vm/vm_zone.h> 67 68 #include <sys/vmmeter.h> 69 #include <sys/thread2.h> 70 #include <sys/signal2.h> 71 #include <sys/spinlock2.h> 72 73 static MALLOC_DEFINE(M_ATFORK, "atfork", "atfork callback"); 74 75 /* 76 * These are the stuctures used to create a callout list for things to do 77 * when forking a process 78 */ 79 struct forklist { 80 forklist_fn function; 81 TAILQ_ENTRY(forklist) next; 82 }; 83 84 TAILQ_HEAD(forklist_head, forklist); 85 static struct forklist_head fork_list = TAILQ_HEAD_INITIALIZER(fork_list); 86 87 static struct lwp *lwp_fork(struct lwp *, struct proc *, int flags); 88 89 int forksleep; /* Place for fork1() to sleep on. */ 90 91 /* 92 * Red-Black tree support for LWPs 93 */ 94 95 static int 96 rb_lwp_compare(struct lwp *lp1, struct lwp *lp2) 97 { 98 if (lp1->lwp_tid < lp2->lwp_tid) 99 return(-1); 100 if (lp1->lwp_tid > lp2->lwp_tid) 101 return(1); 102 return(0); 103 } 104 105 RB_GENERATE2(lwp_rb_tree, lwp, u.lwp_rbnode, rb_lwp_compare, lwpid_t, lwp_tid); 106 107 108 /* ARGSUSED */ 109 int 110 sys_fork(struct fork_args *uap) 111 { 112 struct lwp *lp = curthread->td_lwp; 113 struct proc *p2; 114 int error; 115 116 error = fork1(lp, RFFDG | RFPROC | RFPGLOCK, &p2); 117 if (error == 0) { 118 start_forked_proc(lp, p2); 119 uap->sysmsg_fds[0] = p2->p_pid; 120 uap->sysmsg_fds[1] = 0; 121 } 122 return error; 123 } 124 125 /* ARGSUSED */ 126 int 127 sys_vfork(struct vfork_args *uap) 128 { 129 struct lwp *lp = curthread->td_lwp; 130 struct proc *p2; 131 int error; 132 133 error = fork1(lp, RFFDG | RFPROC | RFPPWAIT | RFMEM | RFPGLOCK, &p2); 134 if (error == 0) { 135 start_forked_proc(lp, p2); 136 uap->sysmsg_fds[0] = p2->p_pid; 137 uap->sysmsg_fds[1] = 0; 138 } 139 return error; 140 } 141 142 /* 143 * Handle rforks. An rfork may (1) operate on the current process without 144 * creating a new, (2) create a new process that shared the current process's 145 * vmspace, signals, and/or descriptors, or (3) create a new process that does 146 * not share these things (normal fork). 147 * 148 * Note that we only call start_forked_proc() if a new process is actually 149 * created. 150 * 151 * rfork { int flags } 152 */ 153 int 154 sys_rfork(struct rfork_args *uap) 155 { 156 struct lwp *lp = curthread->td_lwp; 157 struct proc *p2; 158 int error; 159 160 if ((uap->flags & RFKERNELONLY) != 0) 161 return (EINVAL); 162 163 error = fork1(lp, uap->flags | RFPGLOCK, &p2); 164 if (error == 0) { 165 if (p2) 166 start_forked_proc(lp, p2); 167 uap->sysmsg_fds[0] = p2 ? p2->p_pid : 0; 168 uap->sysmsg_fds[1] = 0; 169 } 170 return error; 171 } 172 173 int 174 sys_lwp_create(struct lwp_create_args *uap) 175 { 176 struct proc *p = curproc; 177 struct lwp *lp; 178 struct lwp_params params; 179 int error; 180 181 error = copyin(uap->params, ¶ms, sizeof(params)); 182 if (error) 183 goto fail2; 184 185 plimit_lwp_fork(p); /* force exclusive access */ 186 lp = lwp_fork(curthread->td_lwp, p, RFPROC); 187 error = cpu_prepare_lwp(lp, ¶ms); 188 if (params.tid1 != NULL && 189 (error = copyout(&lp->lwp_tid, params.tid1, sizeof(lp->lwp_tid)))) 190 goto fail; 191 if (params.tid2 != NULL && 192 (error = copyout(&lp->lwp_tid, params.tid2, sizeof(lp->lwp_tid)))) 193 goto fail; 194 195 /* 196 * Now schedule the new lwp. 197 */ 198 p->p_usched->resetpriority(lp); 199 crit_enter(); 200 lp->lwp_stat = LSRUN; 201 p->p_usched->setrunqueue(lp); 202 crit_exit(); 203 204 return (0); 205 206 fail: 207 lwp_rb_tree_RB_REMOVE(&p->p_lwp_tree, lp); 208 --p->p_nthreads; 209 /* lwp_dispose expects an exited lwp, and a held proc */ 210 lp->lwp_flag |= LWP_WEXIT; 211 lp->lwp_thread->td_flags |= TDF_EXITING; 212 PHOLD(p); 213 lwp_dispose(lp); 214 fail2: 215 return (error); 216 } 217 218 int nprocs = 1; /* process 0 */ 219 220 int 221 fork1(struct lwp *lp1, int flags, struct proc **procp) 222 { 223 struct proc *p1 = lp1->lwp_proc; 224 struct proc *p2, *pptr; 225 struct pgrp *pgrp; 226 uid_t uid; 227 int ok, error; 228 static int curfail = 0; 229 static struct timeval lastfail; 230 struct forklist *ep; 231 struct filedesc_to_leader *fdtol; 232 233 if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG)) 234 return (EINVAL); 235 236 /* 237 * Here we don't create a new process, but we divorce 238 * certain parts of a process from itself. 239 */ 240 if ((flags & RFPROC) == 0) { 241 /* 242 * This kind of stunt does not work anymore if 243 * there are native threads (lwps) running 244 */ 245 if (p1->p_nthreads != 1) 246 return (EINVAL); 247 248 vm_fork(p1, 0, flags); 249 250 /* 251 * Close all file descriptors. 252 */ 253 if (flags & RFCFDG) { 254 struct filedesc *fdtmp; 255 fdtmp = fdinit(p1); 256 fdfree(p1); 257 p1->p_fd = fdtmp; 258 } 259 260 /* 261 * Unshare file descriptors (from parent.) 262 */ 263 if (flags & RFFDG) { 264 if (p1->p_fd->fd_refcnt > 1) { 265 struct filedesc *newfd; 266 newfd = fdcopy(p1); 267 fdfree(p1); 268 p1->p_fd = newfd; 269 } 270 } 271 *procp = NULL; 272 return (0); 273 } 274 275 /* 276 * Interlock against process group signal delivery. If signals 277 * are pending after the interlock is obtained we have to restart 278 * the system call to process the signals. If we don't the child 279 * can miss a pgsignal (such as ^C) sent during the fork. 280 * 281 * We can't use CURSIG() here because it will process any STOPs 282 * and cause the process group lock to be held indefinitely. If 283 * a STOP occurs, the fork will be restarted after the CONT. 284 */ 285 error = 0; 286 pgrp = NULL; 287 if ((flags & RFPGLOCK) && (pgrp = p1->p_pgrp) != NULL) { 288 lockmgr(&pgrp->pg_lock, LK_SHARED); 289 if (CURSIGNB(lp1)) { 290 error = ERESTART; 291 goto done; 292 } 293 } 294 295 /* 296 * Although process entries are dynamically created, we still keep 297 * a global limit on the maximum number we will create. Don't allow 298 * a nonprivileged user to use the last ten processes; don't let root 299 * exceed the limit. The variable nprocs is the current number of 300 * processes, maxproc is the limit. 301 */ 302 uid = p1->p_ucred->cr_ruid; 303 if ((nprocs >= maxproc - 10 && uid != 0) || nprocs >= maxproc) { 304 if (ppsratecheck(&lastfail, &curfail, 1)) 305 kprintf("maxproc limit exceeded by uid %d, please " 306 "see tuning(7) and login.conf(5).\n", uid); 307 tsleep(&forksleep, 0, "fork", hz / 2); 308 error = EAGAIN; 309 goto done; 310 } 311 /* 312 * Increment the nprocs resource before blocking can occur. There 313 * are hard-limits as to the number of processes that can run. 314 */ 315 nprocs++; 316 317 /* 318 * Increment the count of procs running with this uid. Don't allow 319 * a nonprivileged user to exceed their current limit. 320 */ 321 ok = chgproccnt(p1->p_ucred->cr_ruidinfo, 1, 322 (uid != 0) ? p1->p_rlimit[RLIMIT_NPROC].rlim_cur : 0); 323 if (!ok) { 324 /* 325 * Back out the process count 326 */ 327 nprocs--; 328 if (ppsratecheck(&lastfail, &curfail, 1)) 329 kprintf("maxproc limit exceeded by uid %d, please " 330 "see tuning(7) and login.conf(5).\n", uid); 331 tsleep(&forksleep, 0, "fork", hz / 2); 332 error = EAGAIN; 333 goto done; 334 } 335 336 /* Allocate new proc. */ 337 p2 = kmalloc(sizeof(struct proc), M_PROC, M_WAITOK|M_ZERO); 338 339 /* 340 * Setup linkage for kernel based threading XXX lwp 341 */ 342 if (flags & RFTHREAD) { 343 p2->p_peers = p1->p_peers; 344 p1->p_peers = p2; 345 p2->p_leader = p1->p_leader; 346 } else { 347 p2->p_leader = p2; 348 } 349 350 RB_INIT(&p2->p_lwp_tree); 351 spin_init(&p2->p_spin); 352 p2->p_lasttid = -1; /* first tid will be 0 */ 353 354 /* 355 * Setting the state to SIDL protects the partially initialized 356 * process once it starts getting hooked into the rest of the system. 357 */ 358 p2->p_stat = SIDL; 359 proc_add_allproc(p2); 360 361 /* 362 * Make a proc table entry for the new process. 363 * The whole structure was zeroed above, so copy the section that is 364 * copied directly from the parent. 365 */ 366 bcopy(&p1->p_startcopy, &p2->p_startcopy, 367 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 368 369 /* 370 * Duplicate sub-structures as needed. 371 * Increase reference counts on shared objects. 372 */ 373 if (p1->p_flag & P_PROFIL) 374 startprofclock(p2); 375 p2->p_ucred = crhold(p1->p_ucred); 376 377 if (jailed(p2->p_ucred)) 378 p2->p_flag |= P_JAILED; 379 380 if (p2->p_args) 381 p2->p_args->ar_ref++; 382 383 p2->p_usched = p1->p_usched; 384 385 if (flags & RFSIGSHARE) { 386 p2->p_sigacts = p1->p_sigacts; 387 p2->p_sigacts->ps_refcnt++; 388 } else { 389 p2->p_sigacts = (struct sigacts *)kmalloc(sizeof(*p2->p_sigacts), 390 M_SUBPROC, M_WAITOK); 391 bcopy(p1->p_sigacts, p2->p_sigacts, sizeof(*p2->p_sigacts)); 392 p2->p_sigacts->ps_refcnt = 1; 393 } 394 if (flags & RFLINUXTHPN) 395 p2->p_sigparent = SIGUSR1; 396 else 397 p2->p_sigparent = SIGCHLD; 398 399 /* bump references to the text vnode (for procfs) */ 400 p2->p_textvp = p1->p_textvp; 401 if (p2->p_textvp) 402 vref(p2->p_textvp); 403 404 /* 405 * Handle file descriptors 406 */ 407 if (flags & RFCFDG) { 408 p2->p_fd = fdinit(p1); 409 fdtol = NULL; 410 } else if (flags & RFFDG) { 411 p2->p_fd = fdcopy(p1); 412 fdtol = NULL; 413 } else { 414 p2->p_fd = fdshare(p1); 415 if (p1->p_fdtol == NULL) 416 p1->p_fdtol = 417 filedesc_to_leader_alloc(NULL, 418 p1->p_leader); 419 if ((flags & RFTHREAD) != 0) { 420 /* 421 * Shared file descriptor table and 422 * shared process leaders. 423 */ 424 fdtol = p1->p_fdtol; 425 fdtol->fdl_refcount++; 426 } else { 427 /* 428 * Shared file descriptor table, and 429 * different process leaders 430 */ 431 fdtol = filedesc_to_leader_alloc(p1->p_fdtol, p2); 432 } 433 } 434 p2->p_fdtol = fdtol; 435 p2->p_limit = plimit_fork(p1); 436 437 /* 438 * Preserve some more flags in subprocess. P_PROFIL has already 439 * been preserved. 440 */ 441 p2->p_flag |= p1->p_flag & P_SUGID; 442 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 443 p2->p_flag |= P_CONTROLT; 444 if (flags & RFPPWAIT) 445 p2->p_flag |= P_PPWAIT; 446 447 /* 448 * Inherit the virtual kernel structure (allows a virtual kernel 449 * to fork to simulate multiple cpus). 450 */ 451 if (p1->p_vkernel) 452 vkernel_inherit(p1, p2); 453 454 /* 455 * Once we are on a pglist we may receive signals. XXX we might 456 * race a ^C being sent to the process group by not receiving it 457 * at all prior to this line. 458 */ 459 LIST_INSERT_AFTER(p1, p2, p_pglist); 460 461 /* 462 * Attach the new process to its parent. 463 * 464 * If RFNOWAIT is set, the newly created process becomes a child 465 * of init. This effectively disassociates the child from the 466 * parent. 467 */ 468 if (flags & RFNOWAIT) 469 pptr = initproc; 470 else 471 pptr = p1; 472 p2->p_pptr = pptr; 473 LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling); 474 LIST_INIT(&p2->p_children); 475 varsymset_init(&p2->p_varsymset, &p1->p_varsymset); 476 callout_init(&p2->p_ithandle); 477 478 #ifdef KTRACE 479 /* 480 * Copy traceflag and tracefile if enabled. If not inherited, 481 * these were zeroed above but we still could have a trace race 482 * so make sure p2's p_tracenode is NULL. 483 */ 484 if ((p1->p_traceflag & KTRFAC_INHERIT) && p2->p_tracenode == NULL) { 485 p2->p_traceflag = p1->p_traceflag; 486 p2->p_tracenode = ktrinherit(p1->p_tracenode); 487 } 488 #endif 489 490 /* 491 * This begins the section where we must prevent the parent 492 * from being swapped. 493 * 494 * Gets PRELE'd in the caller in start_forked_proc(). 495 */ 496 PHOLD(p1); 497 498 vm_fork(p1, p2, flags); 499 500 /* 501 * Create the first lwp associated with the new proc. 502 * It will return via a different execution path later, directly 503 * into userland, after it was put on the runq by 504 * start_forked_proc(). 505 */ 506 lwp_fork(lp1, p2, flags); 507 508 if (flags == (RFFDG | RFPROC | RFPGLOCK)) { 509 mycpu->gd_cnt.v_forks++; 510 mycpu->gd_cnt.v_forkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize; 511 } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM | RFPGLOCK)) { 512 mycpu->gd_cnt.v_vforks++; 513 mycpu->gd_cnt.v_vforkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize; 514 } else if (p1 == &proc0) { 515 mycpu->gd_cnt.v_kthreads++; 516 mycpu->gd_cnt.v_kthreadpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize; 517 } else { 518 mycpu->gd_cnt.v_rforks++; 519 mycpu->gd_cnt.v_rforkpages += p2->p_vmspace->vm_dsize + p2->p_vmspace->vm_ssize; 520 } 521 522 /* 523 * Both processes are set up, now check if any loadable modules want 524 * to adjust anything. 525 * What if they have an error? XXX 526 */ 527 TAILQ_FOREACH(ep, &fork_list, next) { 528 (*ep->function)(p1, p2, flags); 529 } 530 531 /* 532 * Set the start time. Note that the process is not runnable. The 533 * caller is responsible for making it runnable. 534 */ 535 microtime(&p2->p_start); 536 p2->p_acflag = AFORK; 537 538 /* 539 * tell any interested parties about the new process 540 */ 541 KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid); 542 543 /* 544 * Return child proc pointer to parent. 545 */ 546 *procp = p2; 547 done: 548 if (pgrp) 549 lockmgr(&pgrp->pg_lock, LK_RELEASE); 550 return (error); 551 } 552 553 static struct lwp * 554 lwp_fork(struct lwp *origlp, struct proc *destproc, int flags) 555 { 556 struct lwp *lp; 557 struct thread *td; 558 559 lp = zalloc(lwp_zone); 560 bzero(lp, sizeof(*lp)); 561 562 lp->lwp_proc = destproc; 563 lp->lwp_vmspace = destproc->p_vmspace; 564 lp->lwp_stat = LSRUN; 565 bcopy(&origlp->lwp_startcopy, &lp->lwp_startcopy, 566 (unsigned) ((caddr_t)&lp->lwp_endcopy - 567 (caddr_t)&lp->lwp_startcopy)); 568 lp->lwp_flag |= origlp->lwp_flag & LWP_ALTSTACK; 569 /* 570 * Set cpbase to the last timeout that occured (not the upcoming 571 * timeout). 572 * 573 * A critical section is required since a timer IPI can update 574 * scheduler specific data. 575 */ 576 crit_enter(); 577 lp->lwp_cpbase = mycpu->gd_schedclock.time - 578 mycpu->gd_schedclock.periodic; 579 destproc->p_usched->heuristic_forking(origlp, lp); 580 crit_exit(); 581 lp->lwp_cpumask &= usched_mastermask; 582 583 /* 584 * Assign a TID to the lp. Loop until the insert succeeds (returns 585 * NULL). 586 */ 587 lp->lwp_tid = destproc->p_lasttid; 588 do { 589 if (++lp->lwp_tid < 0) 590 lp->lwp_tid = 1; 591 } while (lwp_rb_tree_RB_INSERT(&destproc->p_lwp_tree, lp) != NULL); 592 destproc->p_lasttid = lp->lwp_tid; 593 destproc->p_nthreads++; 594 595 td = lwkt_alloc_thread(NULL, LWKT_THREAD_STACK, -1, 0); 596 lp->lwp_thread = td; 597 td->td_proc = destproc; 598 td->td_lwp = lp; 599 td->td_switch = cpu_heavy_switch; 600 #ifdef SMP 601 KKASSERT(td->td_mpcount == 1); 602 #endif 603 lwkt_setpri(td, TDPRI_KERN_USER); 604 lwkt_set_comm(td, "%s", destproc->p_comm); 605 606 /* 607 * cpu_fork will copy and update the pcb, set up the kernel stack, 608 * and make the child ready to run. 609 */ 610 cpu_fork(origlp, lp, flags); 611 caps_fork(origlp->lwp_thread, lp->lwp_thread); 612 613 return (lp); 614 } 615 616 /* 617 * The next two functionms are general routines to handle adding/deleting 618 * items on the fork callout list. 619 * 620 * at_fork(): 621 * Take the arguments given and put them onto the fork callout list, 622 * However first make sure that it's not already there. 623 * Returns 0 on success or a standard error number. 624 */ 625 int 626 at_fork(forklist_fn function) 627 { 628 struct forklist *ep; 629 630 #ifdef INVARIANTS 631 /* let the programmer know if he's been stupid */ 632 if (rm_at_fork(function)) { 633 kprintf("WARNING: fork callout entry (%p) already present\n", 634 function); 635 } 636 #endif 637 ep = kmalloc(sizeof(*ep), M_ATFORK, M_WAITOK|M_ZERO); 638 ep->function = function; 639 TAILQ_INSERT_TAIL(&fork_list, ep, next); 640 return (0); 641 } 642 643 /* 644 * Scan the exit callout list for the given item and remove it.. 645 * Returns the number of items removed (0 or 1) 646 */ 647 int 648 rm_at_fork(forklist_fn function) 649 { 650 struct forklist *ep; 651 652 TAILQ_FOREACH(ep, &fork_list, next) { 653 if (ep->function == function) { 654 TAILQ_REMOVE(&fork_list, ep, next); 655 kfree(ep, M_ATFORK); 656 return(1); 657 } 658 } 659 return (0); 660 } 661 662 /* 663 * Add a forked process to the run queue after any remaining setup, such 664 * as setting the fork handler, has been completed. 665 */ 666 void 667 start_forked_proc(struct lwp *lp1, struct proc *p2) 668 { 669 struct lwp *lp2 = ONLY_LWP_IN_PROC(p2); 670 671 /* 672 * Move from SIDL to RUN queue, and activate the process's thread. 673 * Activation of the thread effectively makes the process "a" 674 * current process, so we do not setrunqueue(). 675 * 676 * YYY setrunqueue works here but we should clean up the trampoline 677 * code so we just schedule the LWKT thread and let the trampoline 678 * deal with the userland scheduler on return to userland. 679 */ 680 KASSERT(p2->p_stat == SIDL, 681 ("cannot start forked process, bad status: %p", p2)); 682 p2->p_usched->resetpriority(lp2); 683 crit_enter(); 684 p2->p_stat = SACTIVE; 685 lp2->lwp_stat = LSRUN; 686 p2->p_usched->setrunqueue(lp2); 687 crit_exit(); 688 689 /* 690 * Now can be swapped. 691 */ 692 PRELE(lp1->lwp_proc); 693 694 /* 695 * Preserve synchronization semantics of vfork. If waiting for 696 * child to exec or exit, set P_PPWAIT on child, and sleep on our 697 * proc (in case of exit). 698 */ 699 while (p2->p_flag & P_PPWAIT) 700 tsleep(lp1->lwp_proc, 0, "ppwait", 0); 701 } 702