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kern_fork.c revision 1.191
      1 /*	$NetBSD: kern_fork.c,v 1.191 2012/07/27 20:52:49 christos 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 1.191 2012/07/27 20:52:49 christos 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/pool.h>
     79 #include <sys/mount.h>
     80 #include <sys/proc.h>
     81 #include <sys/ras.h>
     82 #include <sys/resourcevar.h>
     83 #include <sys/vnode.h>
     84 #include <sys/file.h>
     85 #include <sys/acct.h>
     86 #include <sys/ktrace.h>
     87 #include <sys/sched.h>
     88 #include <sys/signalvar.h>
     89 #include <sys/kauth.h>
     90 #include <sys/atomic.h>
     91 #include <sys/syscallargs.h>
     92 #include <sys/uidinfo.h>
     93 #include <sys/sdt.h>
     94 #include <sys/ptrace.h>
     95 
     96 #include <uvm/uvm_extern.h>
     97 
     98 /*
     99  * DTrace SDT provider definitions
    100  */
    101 SDT_PROBE_DEFINE(proc,,,create,
    102 	    "struct proc *", NULL,	/* new process */
    103 	    "struct proc *", NULL,	/* parent process */
    104 	    "int", NULL,		/* flags */
    105 	    NULL, NULL, NULL, NULL);
    106 
    107 u_int	nprocs __cacheline_aligned = 1;		/* process 0 */
    108 
    109 /*
    110  * Number of ticks to sleep if fork() would fail due to process hitting
    111  * limits. Exported in miliseconds to userland via sysctl.
    112  */
    113 int	forkfsleep = 0;
    114 
    115 int
    116 sys_fork(struct lwp *l, const void *v, register_t *retval)
    117 {
    118 
    119 	return fork1(l, 0, SIGCHLD, NULL, 0, NULL, NULL, retval, NULL);
    120 }
    121 
    122 /*
    123  * vfork(2) system call compatible with 4.4BSD (i.e. BSD with Mach VM).
    124  * Address space is not shared, but parent is blocked until child exit.
    125  */
    126 int
    127 sys_vfork(struct lwp *l, const void *v, register_t *retval)
    128 {
    129 
    130 	return fork1(l, FORK_PPWAIT, SIGCHLD, NULL, 0, NULL, NULL,
    131 	    retval, NULL);
    132 }
    133 
    134 /*
    135  * New vfork(2) system call for NetBSD, which implements original 3BSD vfork(2)
    136  * semantics.  Address space is shared, and parent is blocked until child exit.
    137  */
    138 int
    139 sys___vfork14(struct lwp *l, const void *v, register_t *retval)
    140 {
    141 
    142 	return fork1(l, FORK_PPWAIT|FORK_SHAREVM, SIGCHLD, NULL, 0,
    143 	    NULL, NULL, retval, NULL);
    144 }
    145 
    146 /*
    147  * Linux-compatible __clone(2) system call.
    148  */
    149 int
    150 sys___clone(struct lwp *l, const struct sys___clone_args *uap,
    151     register_t *retval)
    152 {
    153 	/* {
    154 		syscallarg(int) flags;
    155 		syscallarg(void *) stack;
    156 	} */
    157 	int flags, sig;
    158 
    159 	/*
    160 	 * We don't support the CLONE_PID or CLONE_PTRACE flags.
    161 	 */
    162 	if (SCARG(uap, flags) & (CLONE_PID|CLONE_PTRACE))
    163 		return EINVAL;
    164 
    165 	/*
    166 	 * Linux enforces CLONE_VM with CLONE_SIGHAND, do same.
    167 	 */
    168 	if (SCARG(uap, flags) & CLONE_SIGHAND
    169 	    && (SCARG(uap, flags) & CLONE_VM) == 0)
    170 		return EINVAL;
    171 
    172 	flags = 0;
    173 
    174 	if (SCARG(uap, flags) & CLONE_VM)
    175 		flags |= FORK_SHAREVM;
    176 	if (SCARG(uap, flags) & CLONE_FS)
    177 		flags |= FORK_SHARECWD;
    178 	if (SCARG(uap, flags) & CLONE_FILES)
    179 		flags |= FORK_SHAREFILES;
    180 	if (SCARG(uap, flags) & CLONE_SIGHAND)
    181 		flags |= FORK_SHARESIGS;
    182 	if (SCARG(uap, flags) & CLONE_VFORK)
    183 		flags |= FORK_PPWAIT;
    184 
    185 	sig = SCARG(uap, flags) & CLONE_CSIGNAL;
    186 	if (sig < 0 || sig >= _NSIG)
    187 		return EINVAL;
    188 
    189 	/*
    190 	 * Note that the Linux API does not provide a portable way of
    191 	 * specifying the stack area; the caller must know if the stack
    192 	 * grows up or down.  So, we pass a stack size of 0, so that the
    193 	 * code that makes this adjustment is a noop.
    194 	 */
    195 	return fork1(l, flags, sig, SCARG(uap, stack), 0,
    196 	    NULL, NULL, retval, NULL);
    197 }
    198 
    199 /*
    200  * Print the 'table full' message once per 10 seconds.
    201  */
    202 static struct timeval fork_tfmrate = { 10, 0 };
    203 
    204 /*
    205  * General fork call.  Note that another LWP in the process may call exec()
    206  * or exit() while we are forking.  It's safe to continue here, because
    207  * neither operation will complete until all LWPs have exited the process.
    208  */
    209 int
    210 fork1(struct lwp *l1, int flags, int exitsig, void *stack, size_t stacksize,
    211     void (*func)(void *), void *arg, register_t *retval,
    212     struct proc **rnewprocp)
    213 {
    214 	struct proc	*p1, *p2, *parent;
    215 	struct plimit   *p1_lim;
    216 	uid_t		uid;
    217 	struct lwp	*l2;
    218 	int		count;
    219 	vaddr_t		uaddr;
    220 	int		tnprocs;
    221 	int		tracefork;
    222 	int		error = 0;
    223 
    224 	p1 = l1->l_proc;
    225 	uid = kauth_cred_getuid(l1->l_cred);
    226 	tnprocs = atomic_inc_uint_nv(&nprocs);
    227 
    228 	/*
    229 	 * Although process entries are dynamically created, we still keep
    230 	 * a global limit on the maximum number we will create.
    231 	 */
    232 	if (__predict_false(tnprocs >= maxproc))
    233 		error = -1;
    234 	else
    235 		error = kauth_authorize_process(l1->l_cred,
    236 		    KAUTH_PROCESS_FORK, p1, KAUTH_ARG(tnprocs), NULL, NULL);
    237 
    238 	if (error) {
    239 		static struct timeval lasttfm;
    240 		atomic_dec_uint(&nprocs);
    241 		if (ratecheck(&lasttfm, &fork_tfmrate))
    242 			tablefull("proc", "increase kern.maxproc or NPROC");
    243 		if (forkfsleep)
    244 			kpause("forkmx", false, forkfsleep, NULL);
    245 		return EAGAIN;
    246 	}
    247 
    248 	/*
    249 	 * Enforce limits.
    250 	 */
    251 	count = chgproccnt(uid, 1);
    252 	if (__predict_false(count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur)) {
    253 		if (kauth_authorize_process(l1->l_cred, KAUTH_PROCESS_RLIMIT,
    254 		    p1, KAUTH_ARG(KAUTH_REQ_PROCESS_RLIMIT_BYPASS),
    255 		    &p1->p_rlimit[RLIMIT_NPROC], KAUTH_ARG(RLIMIT_NPROC)) != 0) {
    256 			(void)chgproccnt(uid, -1);
    257 			atomic_dec_uint(&nprocs);
    258 			if (forkfsleep)
    259 				kpause("forkulim", false, forkfsleep, NULL);
    260 			return EAGAIN;
    261 		}
    262 	}
    263 
    264 	/*
    265 	 * Allocate virtual address space for the U-area now, while it
    266 	 * is still easy to abort the fork operation if we're out of
    267 	 * kernel virtual address space.
    268 	 */
    269 	uaddr = uvm_uarea_alloc();
    270 	if (__predict_false(uaddr == 0)) {
    271 		(void)chgproccnt(uid, -1);
    272 		atomic_dec_uint(&nprocs);
    273 		return ENOMEM;
    274 	}
    275 
    276 	/*
    277 	 * We are now committed to the fork.  From here on, we may
    278 	 * block on resources, but resource allocation may NOT fail.
    279 	 */
    280 
    281 	/* Allocate new proc. */
    282 	p2 = proc_alloc();
    283 
    284 	/*
    285 	 * Make a proc table entry for the new process.
    286 	 * Start by zeroing the section of proc that is zero-initialized,
    287 	 * then copy the section that is copied directly from the parent.
    288 	 */
    289 	memset(&p2->p_startzero, 0,
    290 	    (unsigned) ((char *)&p2->p_endzero - (char *)&p2->p_startzero));
    291 	memcpy(&p2->p_startcopy, &p1->p_startcopy,
    292 	    (unsigned) ((char *)&p2->p_endcopy - (char *)&p2->p_startcopy));
    293 
    294 	CIRCLEQ_INIT(&p2->p_sigpend.sp_info);
    295 
    296 	LIST_INIT(&p2->p_lwps);
    297 	LIST_INIT(&p2->p_sigwaiters);
    298 
    299 	/*
    300 	 * Duplicate sub-structures as needed.
    301 	 * Increase reference counts on shared objects.
    302 	 * Inherit flags we want to keep.  The flags related to SIGCHLD
    303 	 * handling are important in order to keep a consistent behaviour
    304 	 * for the child after the fork.  If we are a 32-bit process, the
    305 	 * child will be too.
    306 	 */
    307 	p2->p_flag =
    308 	    p1->p_flag & (PK_SUGID | PK_NOCLDWAIT | PK_CLDSIGIGN | PK_32);
    309 	p2->p_emul = p1->p_emul;
    310 	p2->p_execsw = p1->p_execsw;
    311 
    312 	if (flags & FORK_SYSTEM) {
    313 		/*
    314 		 * Mark it as a system process.  Set P_NOCLDWAIT so that
    315 		 * children are reparented to init(8) when they exit.
    316 		 * init(8) can easily wait them out for us.
    317 		 */
    318 		p2->p_flag |= (PK_SYSTEM | PK_NOCLDWAIT);
    319 	}
    320 
    321 	mutex_init(&p2->p_stmutex, MUTEX_DEFAULT, IPL_HIGH);
    322 	mutex_init(&p2->p_auxlock, MUTEX_DEFAULT, IPL_NONE);
    323 	rw_init(&p2->p_reflock);
    324 	cv_init(&p2->p_waitcv, "wait");
    325 	cv_init(&p2->p_lwpcv, "lwpwait");
    326 
    327 	/*
    328 	 * Share a lock between the processes if they are to share signal
    329 	 * state: we must synchronize access to it.
    330 	 */
    331 	if (flags & FORK_SHARESIGS) {
    332 		p2->p_lock = p1->p_lock;
    333 		mutex_obj_hold(p1->p_lock);
    334 	} else
    335 		p2->p_lock = mutex_obj_alloc(MUTEX_DEFAULT, IPL_NONE);
    336 
    337 	kauth_proc_fork(p1, p2);
    338 
    339 	p2->p_raslist = NULL;
    340 #if defined(__HAVE_RAS)
    341 	ras_fork(p1, p2);
    342 #endif
    343 
    344 	/* bump references to the text vnode (for procfs) */
    345 	p2->p_textvp = p1->p_textvp;
    346 	if (p2->p_textvp)
    347 		vref(p2->p_textvp);
    348 
    349 	if (flags & FORK_SHAREFILES)
    350 		fd_share(p2);
    351 	else if (flags & FORK_CLEANFILES)
    352 		p2->p_fd = fd_init(NULL);
    353 	else
    354 		p2->p_fd = fd_copy();
    355 
    356 	/* XXX racy */
    357 	p2->p_mqueue_cnt = p1->p_mqueue_cnt;
    358 
    359 	if (flags & FORK_SHARECWD)
    360 		cwdshare(p2);
    361 	else
    362 		p2->p_cwdi = cwdinit();
    363 
    364 	/*
    365 	 * Note: p_limit (rlimit stuff) is copy-on-write, so normally
    366 	 * we just need increase pl_refcnt.
    367 	 */
    368 	p1_lim = p1->p_limit;
    369 	if (!p1_lim->pl_writeable) {
    370 		lim_addref(p1_lim);
    371 		p2->p_limit = p1_lim;
    372 	} else {
    373 		p2->p_limit = lim_copy(p1_lim);
    374 	}
    375 
    376 	if (flags & FORK_PPWAIT) {
    377 		/* Mark ourselves as waiting for a child. */
    378 		l1->l_pflag |= LP_VFORKWAIT;
    379 		p2->p_lflag = PL_PPWAIT;
    380 		p2->p_vforklwp = l1;
    381 	} else {
    382 		p2->p_lflag = 0;
    383 	}
    384 	p2->p_sflag = 0;
    385 	p2->p_slflag = 0;
    386 	parent = (flags & FORK_NOWAIT) ? initproc : p1;
    387 	p2->p_pptr = parent;
    388 	p2->p_ppid = parent->p_pid;
    389 	LIST_INIT(&p2->p_children);
    390 
    391 	p2->p_aio = NULL;
    392 
    393 #ifdef KTRACE
    394 	/*
    395 	 * Copy traceflag and tracefile if enabled.
    396 	 * If not inherited, these were zeroed above.
    397 	 */
    398 	if (p1->p_traceflag & KTRFAC_INHERIT) {
    399 		mutex_enter(&ktrace_lock);
    400 		p2->p_traceflag = p1->p_traceflag;
    401 		if ((p2->p_tracep = p1->p_tracep) != NULL)
    402 			ktradref(p2);
    403 		mutex_exit(&ktrace_lock);
    404 	}
    405 #endif
    406 
    407 	/*
    408 	 * Create signal actions for the child process.
    409 	 */
    410 	p2->p_sigacts = sigactsinit(p1, flags & FORK_SHARESIGS);
    411 	mutex_enter(p1->p_lock);
    412 	p2->p_sflag |=
    413 	    (p1->p_sflag & (PS_STOPFORK | PS_STOPEXEC | PS_NOCLDSTOP));
    414 	sched_proc_fork(p1, p2);
    415 	mutex_exit(p1->p_lock);
    416 
    417 	p2->p_stflag = p1->p_stflag;
    418 
    419 	/*
    420 	 * p_stats.
    421 	 * Copy parts of p_stats, and zero out the rest.
    422 	 */
    423 	p2->p_stats = pstatscopy(p1->p_stats);
    424 
    425 	/*
    426 	 * Set up the new process address space.
    427 	 */
    428 	uvm_proc_fork(p1, p2, (flags & FORK_SHAREVM) ? true : false);
    429 
    430 	/*
    431 	 * Finish creating the child process.
    432 	 * It will return through a different path later.
    433 	 */
    434 	lwp_create(l1, p2, uaddr, (flags & FORK_PPWAIT) ? LWP_VFORK : 0,
    435 	    stack, stacksize, (func != NULL) ? func : child_return, arg, &l2,
    436 	    l1->l_class);
    437 
    438 	/*
    439 	 * Inherit l_private from the parent.
    440 	 * Note that we cannot use lwp_setprivate() here since that
    441 	 * also sets the CPU TLS register, which is incorrect if the
    442 	 * process has changed that without letting the kernel know.
    443 	 */
    444 	l2->l_private = l1->l_private;
    445 
    446 	/*
    447 	 * If emulation has a process fork hook, call it now.
    448 	 */
    449 	if (p2->p_emul->e_proc_fork)
    450 		(*p2->p_emul->e_proc_fork)(p2, l1, flags);
    451 
    452 	/*
    453 	 * ...and finally, any other random fork hooks that subsystems
    454 	 * might have registered.
    455 	 */
    456 	doforkhooks(p2, p1);
    457 
    458 	SDT_PROBE(proc,,,create, p2, p1, flags, 0, 0);
    459 
    460 	/*
    461 	 * It's now safe for the scheduler and other processes to see the
    462 	 * child process.
    463 	 */
    464 	mutex_enter(proc_lock);
    465 
    466 	if (p1->p_session->s_ttyvp != NULL && p1->p_lflag & PL_CONTROLT)
    467 		p2->p_lflag |= PL_CONTROLT;
    468 
    469 	LIST_INSERT_HEAD(&parent->p_children, p2, p_sibling);
    470 	p2->p_exitsig = exitsig;		/* signal for parent on exit */
    471 
    472 	/*
    473 	 * We don't want to tracefork vfork()ed processes because they
    474 	 * will not receive the SIGTRAP until it is too late.
    475 	 */
    476 	tracefork = (p1->p_slflag & (PSL_TRACEFORK|PSL_TRACED)) ==
    477 	    (PSL_TRACEFORK|PSL_TRACED) && (flags && FORK_PPWAIT) == 0;
    478 	if (tracefork) {
    479 		p2->p_slflag |= PSL_TRACED;
    480 		p2->p_opptr = p2->p_pptr;
    481 		if (p2->p_pptr != p1->p_pptr) {
    482 			struct proc *parent1 = p2->p_pptr;
    483 
    484 			if (parent1->p_lock < p2->p_lock) {
    485 				if (!mutex_tryenter(parent1->p_lock)) {
    486 					mutex_exit(p2->p_lock);
    487 					mutex_enter(parent1->p_lock);
    488 				}
    489 			} else if (parent1->p_lock > p2->p_lock) {
    490 				mutex_enter(parent1->p_lock);
    491 			}
    492 			parent1->p_slflag |= PSL_CHTRACED;
    493 			proc_reparent(p2, p1->p_pptr);
    494 			if (parent1->p_lock != p2->p_lock)
    495 				mutex_exit(parent1->p_lock);
    496 		}
    497 
    498 		/*
    499 		 * Set ptrace status.
    500 		 */
    501 		p1->p_fpid = p2->p_pid;
    502 		p2->p_fpid = p1->p_pid;
    503 	}
    504 
    505 	LIST_INSERT_AFTER(p1, p2, p_pglist);
    506 	LIST_INSERT_HEAD(&allproc, p2, p_list);
    507 
    508 	p2->p_trace_enabled = trace_is_enabled(p2);
    509 #ifdef __HAVE_SYSCALL_INTERN
    510 	(*p2->p_emul->e_syscall_intern)(p2);
    511 #endif
    512 
    513 	/*
    514 	 * Update stats now that we know the fork was successful.
    515 	 */
    516 	uvmexp.forks++;
    517 	if (flags & FORK_PPWAIT)
    518 		uvmexp.forks_ppwait++;
    519 	if (flags & FORK_SHAREVM)
    520 		uvmexp.forks_sharevm++;
    521 
    522 	/*
    523 	 * Pass a pointer to the new process to the caller.
    524 	 */
    525 	if (rnewprocp != NULL)
    526 		*rnewprocp = p2;
    527 
    528 	if (ktrpoint(KTR_EMUL))
    529 		p2->p_traceflag |= KTRFAC_TRC_EMUL;
    530 
    531 	/*
    532 	 * Notify any interested parties about the new process.
    533 	 */
    534 	if (!SLIST_EMPTY(&p1->p_klist)) {
    535 		mutex_exit(proc_lock);
    536 		KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid);
    537 		mutex_enter(proc_lock);
    538 	}
    539 
    540 	/*
    541 	 * Make child runnable, set start time, and add to run queue except
    542 	 * if the parent requested the child to start in SSTOP state.
    543 	 */
    544 	mutex_enter(p2->p_lock);
    545 
    546 	/*
    547 	 * Start profiling.
    548 	 */
    549 	if ((p2->p_stflag & PST_PROFIL) != 0) {
    550 		mutex_spin_enter(&p2->p_stmutex);
    551 		startprofclock(p2);
    552 		mutex_spin_exit(&p2->p_stmutex);
    553 	}
    554 
    555 	getmicrotime(&p2->p_stats->p_start);
    556 	p2->p_acflag = AFORK;
    557 	lwp_lock(l2);
    558 	KASSERT(p2->p_nrlwps == 1);
    559 	if (p2->p_sflag & PS_STOPFORK) {
    560 		struct schedstate_percpu *spc = &l2->l_cpu->ci_schedstate;
    561 		p2->p_nrlwps = 0;
    562 		p2->p_stat = SSTOP;
    563 		p2->p_waited = 0;
    564 		p1->p_nstopchild++;
    565 		l2->l_stat = LSSTOP;
    566 		KASSERT(l2->l_wchan == NULL);
    567 		lwp_unlock_to(l2, spc->spc_lwplock);
    568 	} else {
    569 		p2->p_nrlwps = 1;
    570 		p2->p_stat = SACTIVE;
    571 		l2->l_stat = LSRUN;
    572 		sched_enqueue(l2, false);
    573 		lwp_unlock(l2);
    574 	}
    575 
    576 	/*
    577 	 * Return child pid to parent process,
    578 	 * marking us as parent via retval[1].
    579 	 */
    580 	if (retval != NULL) {
    581 		retval[0] = p2->p_pid;
    582 		retval[1] = 0;
    583 	}
    584 	mutex_exit(p2->p_lock);
    585 
    586 	/*
    587 	 * Preserve synchronization semantics of vfork.  If waiting for
    588 	 * child to exec or exit, sleep until it clears LP_VFORKWAIT.
    589 	 */
    590 #if 0
    591 	while (l1->l_pflag & LP_VFORKWAIT) {
    592 		cv_wait(&l1->l_waitcv, proc_lock);
    593 	}
    594 #else
    595 	while (p2->p_lflag & PL_PPWAIT)
    596 		cv_wait(&p1->p_waitcv, proc_lock);
    597 #endif
    598 
    599 	/*
    600 	 * Let the parent know that we are tracing its child.
    601 	 */
    602 	if (tracefork) {
    603 		ksiginfo_t ksi;
    604 
    605 		KSI_INIT_EMPTY(&ksi);
    606 		ksi.ksi_signo = SIGTRAP;
    607 		ksi.ksi_lid = l1->l_lid;
    608 		kpsignal(p1, &ksi, NULL);
    609 	}
    610 	mutex_exit(proc_lock);
    611 
    612 	return 0;
    613 }
    614