xref: /src/sys/kern/kern_fork.c

/*	$NetBSD: kern_fork.c,v 1.76 2000/11/08 05:16:23 chs Exp $	*/

/*
 * Copyright (c) 1982, 1986, 1989, 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)kern_fork.c	8.8 (Berkeley) 2/14/95
 */

#include "opt_ktrace.h"
#include "opt_multiprocessor.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/map.h>
#include <sys/filedesc.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/pool.h>
#include <sys/mount.h>
#include <sys/proc.h>
#include <sys/resourcevar.h>
#include <sys/vnode.h>
#include <sys/file.h>
#include <sys/acct.h>
#include <sys/ktrace.h>
#include <sys/vmmeter.h>
#include <sys/sched.h>
#include <sys/signalvar.h>

#include <sys/syscallargs.h>

#include <uvm/uvm_extern.h>

int	nprocs = 1;		/* process 0 */

/*ARGSUSED*/
int
sys_fork(struct proc *p, void *v, register_t *retval)
{

	return (fork1(p, 0, SIGCHLD, NULL, 0, NULL, NULL, retval, NULL));
}

/*
 * vfork(2) system call compatible with 4.4BSD (i.e. BSD with Mach VM).
 * Address space is not shared, but parent is blocked until child exit.
 */
/*ARGSUSED*/
int
sys_vfork(struct proc *p, void *v, register_t *retval)
{

	return (fork1(p, FORK_PPWAIT, SIGCHLD, NULL, 0, NULL, NULL,
	    retval, NULL));
}

/*
 * New vfork(2) system call for NetBSD, which implements original 3BSD vfork(2)
 * semantics.  Address space is shared, and parent is blocked until child exit.
 */
/*ARGSUSED*/
int
sys___vfork14(struct proc *p, void *v, register_t *retval)
{

	return (fork1(p, FORK_PPWAIT|FORK_SHAREVM, SIGCHLD, NULL, 0,
	    NULL, NULL, retval, NULL));
}

int
fork1(struct proc *p1, int flags, int exitsig, void *stack, size_t stacksize,
    void (*func)(void *), void *arg, register_t *retval,
    struct proc **rnewprocp)
{
	struct proc *p2, *tp;
	uid_t uid;
	int count, s;
	vaddr_t uaddr;
	static int nextpid, pidchecked = 0;

	/*
	 * Although process entries are dynamically created, we still keep
	 * a global limit on the maximum number we will create.  Don't allow
	 * a nonprivileged user to use the last process; don't let root
	 * exceed the limit. The variable nprocs is the current number of
	 * processes, maxproc is the limit.
	 */
	uid = p1->p_cred->p_ruid;
	if (__predict_false((nprocs >= maxproc - 1 && uid != 0) ||
			    nprocs >= maxproc)) {
		tablefull("proc", "increase kern.maxproc or NPROC");
		return (EAGAIN);
	}
	nprocs++;

	/*
	 * Increment the count of procs running with this uid. Don't allow
	 * a nonprivileged user to exceed their current limit.
	 */
	count = chgproccnt(uid, 1);
	if (__predict_false(uid != 0 && count >
			    p1->p_rlimit[RLIMIT_NPROC].rlim_cur)) {
		(void)chgproccnt(uid, -1);
		nprocs--;
		return (EAGAIN);
	}

	/*
	 * Allocate virtual address space for the U-area now, while it
	 * is still easy to abort the fork operation if we're out of
	 * kernel virtual address space.  The actual U-area pages will
	 * be allocated and wired in vm_fork().
	 */
	uaddr = uvm_km_valloc(kernel_map, USPACE);
	if (__predict_false(uaddr == 0)) {
		(void)chgproccnt(uid, -1);
		nprocs--;
		return (ENOMEM);
	}

	/*
	 * We are now committed to the fork.  From here on, we may
	 * block on resources, but resource allocation may NOT fail.
	 */

	/* Allocate new proc. */
	p2 = pool_get(&proc_pool, PR_WAITOK);

	/*
	 * Make a proc table entry for the new process.
	 * Start by zeroing the section of proc that is zero-initialized,
	 * then copy the section that is copied directly from the parent.
	 */
	memset(&p2->p_startzero, 0,
	    (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero));
	memcpy(&p2->p_startcopy, &p1->p_startcopy,
	    (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy));

#if !defined(MULTIPROCESSOR)
	/*
	 * In the single-processor case, all processes will always run
	 * on the same CPU.  So, initialize the child's CPU to the parent's
	 * now.  In the multiprocessor case, the child's CPU will be
	 * initialized in the low-level context switch code when the
	 * process runs.
	 */
	p2->p_cpu = p1->p_cpu;
#else
	/*
	 * zero child's cpu pointer so we don't get trash.
	 */
	p2->p_cpu = NULL;
#endif /* ! MULTIPROCESSOR */

	/*
	 * Duplicate sub-structures as needed.
	 * Increase reference counts on shared objects.
	 * The p_stats and p_sigacts substructs are set in uvm_fork().
	 */
	p2->p_flag = P_INMEM | (p1->p_flag & P_SUGID);
	p2->p_emul = p1->p_emul;
	if (p1->p_flag & P_PROFIL)
		startprofclock(p2);
	p2->p_cred = pool_get(&pcred_pool, PR_WAITOK);
	memcpy(p2->p_cred, p1->p_cred, sizeof(*p2->p_cred));
	p2->p_cred->p_refcnt = 1;
	crhold(p1->p_ucred);

	/* bump references to the text vnode (for procfs) */
	p2->p_textvp = p1->p_textvp;
	if (p2->p_textvp)
		VREF(p2->p_textvp);

	if (flags & FORK_SHAREFILES)
		fdshare(p1, p2);
	else
		p2->p_fd = fdcopy(p1);

	if (flags & FORK_SHARECWD)
		cwdshare(p1, p2);
	else
		p2->p_cwdi = cwdinit(p1);

	/*
	 * If p_limit is still copy-on-write, bump refcnt,
	 * otherwise get a copy that won't be modified.
	 * (If PL_SHAREMOD is clear, the structure is shared
	 * copy-on-write.)
	 */
	if (p1->p_limit->p_lflags & PL_SHAREMOD)
		p2->p_limit = limcopy(p1->p_limit);
	else {
		p2->p_limit = p1->p_limit;
		p2->p_limit->p_refcnt++;
	}

	if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
		p2->p_flag |= P_CONTROLT;
	if (flags & FORK_PPWAIT)
		p2->p_flag |= P_PPWAIT;
	LIST_INSERT_AFTER(p1, p2, p_pglist);
	p2->p_pptr = p1;
	LIST_INSERT_HEAD(&p1->p_children, p2, p_sibling);
	LIST_INIT(&p2->p_children);

	callout_init(&p2->p_realit_ch);
	callout_init(&p2->p_tsleep_ch);

#ifdef KTRACE
	/*
	 * Copy traceflag and tracefile if enabled.
	 * If not inherited, these were zeroed above.
	 */
	if (p1->p_traceflag&KTRFAC_INHERIT) {
		p2->p_traceflag = p1->p_traceflag;
		if ((p2->p_tracep = p1->p_tracep) != NULL)
			ktradref(p2);
	}
#endif
	scheduler_fork_hook(p1, p2);

	/*
	 * Create signal actions for the child process.
	 */
	if (flags & FORK_SHARESIGS)
		sigactsshare(p1, p2);
	else
		p2->p_sigacts = sigactsinit(p1);

	/*
	 * If emulation has process fork hook, call it now.
	 */
	if (p2->p_emul->e_proc_fork)
		(*p2->p_emul->e_proc_fork)(p2, p1);

	/*
	 * This begins the section where we must prevent the parent
	 * from being swapped.
	 */
	PHOLD(p1);

	/*
	 * Finish creating the child process.  It will return through a
	 * different path later.
	 */
	p2->p_addr = (struct user *)uaddr;
	uvm_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE,
	    stack, stacksize,
	    (func != NULL) ? func : child_return,
	    (arg != NULL) ? arg : p2);

	/*
	 * BEGIN PID ALLOCATION.
	 */
	s = proclist_lock_write();

	/*
	 * Find an unused process ID.  We remember a range of unused IDs
	 * ready to use (from nextpid+1 through pidchecked-1).
	 */
	nextpid++;
retry:
	/*
	 * If the process ID prototype has wrapped around,
	 * restart somewhat above 0, as the low-numbered procs
	 * tend to include daemons that don't exit.
	 */
	if (nextpid >= PID_MAX) {
		nextpid = 100;
		pidchecked = 0;
	}
	if (nextpid >= pidchecked) {
		const struct proclist_desc *pd;

		pidchecked = PID_MAX;
		/*
		 * Scan the process lists to check whether this pid
		 * is in use.  Remember the lowest pid that's greater
		 * than nextpid, so we can avoid checking for a while.
		 */
		pd = proclists;
again:
		LIST_FOREACH(tp, pd->pd_list, p_list) {
			while (tp->p_pid == nextpid ||
			    tp->p_pgrp->pg_id == nextpid ||
			    tp->p_session->s_sid == nextpid) {
				nextpid++;
				if (nextpid >= pidchecked)
					goto retry;
			}
			if (tp->p_pid > nextpid && pidchecked > tp->p_pid)
				pidchecked = tp->p_pid;

			if (tp->p_pgrp->pg_id > nextpid &&
			    pidchecked > tp->p_pgrp->pg_id)
				pidchecked = tp->p_pgrp->pg_id;

			if (tp->p_session->s_sid > nextpid &&
			    pidchecked > tp->p_session->s_sid)
				pidchecked = tp->p_session->s_sid;
		}

		/*
		 * If there's another list, scan it.  If we have checked
		 * them all, we've found one!
		 */
		pd++;
		if (pd->pd_list != NULL)
			goto again;
	}

	/* Record the pid we've allocated. */
	p2->p_pid = nextpid;

	/* Record the signal to be delivered to the parent on exit. */
	p2->p_exitsig = exitsig;

	/*
	 * Put the proc on allproc before unlocking PID allocation
	 * so that waiters won't grab it as soon as we unlock.
	 */

	p2->p_stat = SIDL;			/* protect against others */
	p2->p_forw = p2->p_back = NULL;		/* shouldn't be necessary */

	LIST_INSERT_HEAD(&allproc, p2, p_list);

	LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);

	/*
	 * END PID ALLOCATION.
	 */
	proclist_unlock_write(s);

	/*
	 * Make child runnable, set start time, and add to run queue.
	 */
	SCHED_LOCK(s);
	p2->p_stats->p_start = time;
	p2->p_acflag = AFORK;
	p2->p_stat = SRUN;
	setrunqueue(p2);
	SCHED_UNLOCK(s);

	/*
	 * Now can be swapped.
	 */
	PRELE(p1);

	/*
	 * Update stats now that we know the fork was successful.
	 */
	uvmexp.forks++;
	if (flags & FORK_PPWAIT)
		uvmexp.forks_ppwait++;
	if (flags & FORK_SHAREVM)
		uvmexp.forks_sharevm++;

	/*
	 * Pass a pointer to the new process to the caller.
	 */
	if (rnewprocp != NULL)
		*rnewprocp = p2;

	/*
	 * Preserve synchronization semantics of vfork.  If waiting for
	 * child to exec or exit, set P_PPWAIT on child, and sleep on our
	 * proc (in case of exit).
	 */
	if (flags & FORK_PPWAIT)
		while (p2->p_flag & P_PPWAIT)
			tsleep(p1, PWAIT, "ppwait", 0);

	/*
	 * Return child pid to parent process,
	 * marking us as parent via retval[1].
	 */
	if (retval != NULL) {
		retval[0] = p2->p_pid;
		retval[1] = 0;
	}

#ifdef KTRACE
	if (KTRPOINT(p2, KTR_EMUL))
		ktremul(p2);
#endif

	return (0);
}

#if defined(MULTIPROCESSOR)
/*
 * XXX This is a slight hack to get newly-formed processes to
 * XXX acquire the kernel lock as soon as they run.
 */
void
proc_trampoline_mp(void)
{
	struct proc *p = curproc;

	SCHED_ASSERT_UNLOCKED();
	KERNEL_PROC_LOCK(p);
}
#endif