common/os/fork.c

	fork.c revision d3e55dcdc881b833a707e39ae1e12d8d5d35ad2d
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*  Copyright (c) 1984, 1986, 1987, 1988, 1989 AT&T */
/*    All Rights Reserved   */

#pragma ident   "%Z%%M% %I% %E% SMI"

#include <sys/types.h>
#include <sys/param.h>
#include <sys/sysmacros.h>
#include <sys/signal.h>
#include <sys/cred.h>
#include <sys/policy.h>
#include <sys/user.h>
#include <sys/systm.h>
#include <sys/cpuvar.h>
#include <sys/vfs.h>
#include <sys/vnode.h>
#include <sys/file.h>
#include <sys/errno.h>
#include <sys/time.h>
#include <sys/proc.h>
#include <sys/cmn_err.h>
#include <sys/acct.h>
#include <sys/tuneable.h>
#include <sys/class.h>
#include <sys/kmem.h>
#include <sys/session.h>
#include <sys/ucontext.h>
#include <sys/stack.h>
#include <sys/procfs.h>
#include <sys/prsystm.h>
#include <sys/vmsystm.h>
#include <sys/vtrace.h>
#include <sys/debug.h>
#include <sys/shm_impl.h>
#include <sys/door_data.h>
#include <vm/as.h>
#include <vm/rm.h>
#include <c2/audit.h>
#include <sys/var.h>
#include <sys/schedctl.h>
#include <sys/utrap.h>
#include <sys/task.h>
#include <sys/resource.h>
#include <sys/cyclic.h>
#include <sys/lgrp.h>
#include <sys/rctl.h>
#include <sys/contract_impl.h>
#include <sys/contract/process_impl.h>
#include <sys/list.h>
#include <sys/dtrace.h>
#include <sys/pool.h>
#include <sys/zone.h>
#include <sys/sdt.h>
#include <sys/class.h>
#include <sys/corectl.h>
#include <sys/brand.h>
#include <sys/fork.h>

static int64_t cfork(int, int, int);
static int getproc(proc_t **, int);
static void fork_fail(proc_t *);
static void forklwp_fail(proc_t *);

int fork_fail_pending;

extern struct kmem_cache *process_cache;

/*
 * forkall system call.
 */
int64_t
forkall(void)
{
    return (cfork(0, 0, 0));
}

/*
 * The parent is stopped until the child invokes relvm().
 */
int64_t
vfork(void)
{
    curthread->t_post_sys = 1;  /* so vfwait() will be called */
    return (cfork(1, 1, 0));
}

/*
 * fork system call, aka fork1.
 */
int64_t
fork1(void)
{
    return (cfork(0, 1, 0));
}

/*
 * The forkall(), vfork(), and fork1() system calls are no longer
 * invoked by libc.  They are retained only for the benefit of
 * old statically-linked applications.  They should be eliminated
 * when we no longer care about such old and broken applications.
 */

/*
 * forksys system call - forkx, forkallx, vforkx.
 * This is the interface now invoked by libc.
 */
int64_t
forksys(int subcode, int flags)
{
    switch (subcode) {
    case 0:
        return (cfork(0, 1, flags));    /* forkx(flags) */
    case 1:
        return (cfork(0, 0, flags));    /* forkallx(flags) */
    case 2:
        curthread->t_post_sys = 1;  /* so vfwait() will be called */
        return (cfork(1, 1, flags));    /* vforkx(flags) */
    default:
        return ((int64_t)set_errno(EINVAL));
    }
}

/* ARGSUSED */
static int64_t
cfork(int isvfork, int isfork1, int flags)
{
    proc_t *p = ttoproc(curthread);
    struct as *as;
    proc_t *cp, **orphpp;
    klwp_t *clone;
    kthread_t *t;
    task_t *tk;
    rval_t  r;
    int error;
    int i;
    rctl_set_t *dup_set;
    rctl_alloc_gp_t *dup_gp;
    rctl_entity_p_t e;
    lwpdir_t *ldp;
    lwpent_t *lep;
    lwpent_t *clep;

    /*
     * Allow only these two flags.
     */
    if ((flags & ~(FORK_NOSIGCHLD | FORK_WAITPID)) != 0) {
        error = EINVAL;
        goto forkerr;
    }

    /*
     * fork is not supported for the /proc agent lwp.
     */
    if (curthread == p->p_agenttp) {
        error = ENOTSUP;
        goto forkerr;
    }

    if ((error = secpolicy_basic_fork(CRED())) != 0)
        goto forkerr;

    /*
     * If the calling lwp is doing a fork1() then the
     * other lwps in this process are not duplicated and
     * don't need to be held where their kernel stacks can be
     * cloned.  If doing forkall(), the process is held with
     * SHOLDFORK, so that the lwps are at a point where their
     * stacks can be copied which is on entry or exit from
     * the kernel.
     */
    if (!holdlwps(isfork1 ? SHOLDFORK1 : SHOLDFORK)) {
        aston(curthread);
        error = EINTR;
        goto forkerr;
    }

#if defined(__sparc)
    /*
     * Ensure that the user stack is fully constructed
     * before creating the child process structure.
     */
    (void) flush_user_windows_to_stack(NULL);
#endif

    mutex_enter(&p->p_lock);
    /*
     * If this is vfork(), cancel any suspend request we might
     * have gotten from some other thread via lwp_suspend().
     * Otherwise we could end up with a deadlock on return
     * from the vfork() in both the parent and the child.
     */
    if (isvfork)
        curthread->t_proc_flag &= ~TP_HOLDLWP;
    /*
     * Prevent our resource set associations from being changed during fork.
     */
    pool_barrier_enter();
    mutex_exit(&p->p_lock);

    /*
     * Create a child proc struct. Place a VN_HOLD on appropriate vnodes.
     */
    if (getproc(&cp, 0) < 0) {
        mutex_enter(&p->p_lock);
        pool_barrier_exit();
        continuelwps(p);
        mutex_exit(&p->p_lock);
        error = EAGAIN;
        goto forkerr;
    }

    TRACE_2(TR_FAC_PROC, TR_PROC_FORK, "proc_fork:cp %p p %p", cp, p);

    /*
     * Assign an address space to child
     */
    if (isvfork) {
        /*
         * Clear any watched areas and remember the
         * watched pages for restoring in vfwait().
         */
        as = p->p_as;
        if (avl_numnodes(&as->a_wpage) != 0) {
            AS_LOCK_ENTER(as, &as->a_lock, RW_WRITER);
            as_clearwatch(as);
            p->p_wpage = as->a_wpage;
            avl_create(&as->a_wpage, wp_compare,
                sizeof (struct watched_page),
                offsetof(struct watched_page, wp_link));
            AS_LOCK_EXIT(as, &as->a_lock);
        }
        cp->p_as = as;
        cp->p_flag |= SVFORK;
    } else {
        /*
         * We need to hold P_PR_LOCK until the address space has
         * been duplicated and we've had a chance to remove from the
         * child any DTrace probes that were in the parent. Holding
         * P_PR_LOCK prevents any new probes from being added and any
         * extant probes from being removed.
         */
        mutex_enter(&p->p_lock);
        sprlock_proc(p);
        p->p_flag |= SFORKING;
        mutex_exit(&p->p_lock);

        error = as_dup(p->p_as, &cp->p_as);
        if (error != 0) {
            mutex_enter(&p->p_lock);
            sprunlock(p);
            fork_fail(cp);
            mutex_enter(&pidlock);
            orphpp = &p->p_orphan;
            while (*orphpp != cp)
                orphpp = &(*orphpp)->p_nextorph;
            *orphpp = cp->p_nextorph;
            if (p->p_child == cp)
                p->p_child = cp->p_sibling;
            if (cp->p_sibling)
                cp->p_sibling->p_psibling = cp->p_psibling;
            if (cp->p_psibling)
                cp->p_psibling->p_sibling = cp->p_sibling;
            mutex_enter(&cp->p_lock);
            tk = cp->p_task;
            task_detach(cp);
            ASSERT(cp->p_pool->pool_ref > 0);
            atomic_add_32(&cp->p_pool->pool_ref, -1);
            mutex_exit(&cp->p_lock);
            pid_exit(cp);
            mutex_exit(&pidlock);
            task_rele(tk);

            mutex_enter(&p->p_lock);
            p->p_flag &= ~SFORKING;
            pool_barrier_exit();
            continuelwps(p);
            mutex_exit(&p->p_lock);
            /*
             * Preserve ENOMEM error condition but
             * map all others to EAGAIN.
             */
            error = (error == ENOMEM) ? ENOMEM : EAGAIN;
            goto forkerr;
        }
        cp->p_as->a_proc = cp;

        /* Duplicate parent's shared memory */
        if (p->p_segacct)
            shmfork(p, cp);

        /*
         * Remove all DTrace tracepoints from the child process. We
         * need to do this _before_ duplicating USDT providers since
         * any associated probes may be immediately enabled.
         */
        if (p->p_dtrace_count > 0)
            dtrace_fasttrap_fork(p, cp);

        /*
         * Duplicate any helper actions and providers. The SFORKING
         * we set above informs the code to enable USDT probes that
         * sprlock() may fail because the child is being forked.
         */
        if (p->p_dtrace_helpers != NULL) {
            mutex_enter(&p->p_lock);
            sprunlock(p);

            ASSERT(dtrace_helpers_fork != NULL);
            (*dtrace_helpers_fork)(p, cp);

            mutex_enter(&p->p_lock);
            p->p_flag &= ~SFORKING;
            mutex_exit(&p->p_lock);
        } else {
            mutex_enter(&p->p_lock);
            p->p_flag &= ~SFORKING;
            sprunlock(p);
        }
    }

    /*
     * Duplicate parent's resource controls.
     */
    dup_set = rctl_set_create();
    for (;;) {
        dup_gp = rctl_set_dup_prealloc(p->p_rctls);
        mutex_enter(&p->p_rctls->rcs_lock);
        if (rctl_set_dup_ready(p->p_rctls, dup_gp))
            break;
        mutex_exit(&p->p_rctls->rcs_lock);
        rctl_prealloc_destroy(dup_gp);
    }
    e.rcep_p.proc = cp;
    e.rcep_t = RCENTITY_PROCESS;
    cp->p_rctls = rctl_set_dup(p->p_rctls, p, cp, &e, dup_set, dup_gp,
        RCD_DUP | RCD_CALLBACK);
    mutex_exit(&p->p_rctls->rcs_lock);

    rctl_prealloc_destroy(dup_gp);

    /*
     * Allocate the child's lwp directory and lwpid hash table.
     */
    if (isfork1)
        cp->p_lwpdir_sz = 2;
    else
        cp->p_lwpdir_sz = p->p_lwpdir_sz;
    cp->p_lwpdir = cp->p_lwpfree = ldp =
        kmem_zalloc(cp->p_lwpdir_sz * sizeof (lwpdir_t), KM_SLEEP);
    for (i = 1; i < cp->p_lwpdir_sz; i++, ldp++)
        ldp->ld_next = ldp + 1;
    cp->p_tidhash_sz = (cp->p_lwpdir_sz + 2) / 2;
    cp->p_tidhash =
        kmem_zalloc(cp->p_tidhash_sz * sizeof (lwpdir_t *), KM_SLEEP);

    /*
     * Duplicate parent's lwps.
     * Mutual exclusion is not needed because the process is
     * in the hold state and only the current lwp is running.
     */
    klgrpset_clear(cp->p_lgrpset);
    if (isfork1) {
        clone = forklwp(ttolwp(curthread), cp, curthread->t_tid);
        if (clone == NULL)
            goto forklwperr;
        /*
         * Inherit only the lwp_wait()able flag,
         * Daemon threads should not call fork1(), but oh well...
         */
        lwptot(clone)->t_proc_flag |=
            (curthread->t_proc_flag & TP_TWAIT);
    } else {
        /* this is forkall(), no one can be in lwp_wait() */
        ASSERT(p->p_lwpwait == 0 && p->p_lwpdwait == 0);
        /* for each entry in the parent's lwp directory... */
        for (i = 0, ldp = p->p_lwpdir; i < p->p_lwpdir_sz; i++, ldp++) {
            klwp_t *clwp;
            kthread_t *ct;

            if ((lep = ldp->ld_entry) == NULL)
                continue;

            if ((t = lep->le_thread) != NULL) {
                clwp = forklwp(ttolwp(t), cp, t->t_tid);
                if (clwp == NULL)
                    goto forklwperr;
                ct = lwptot(clwp);
                /*
                 * Inherit lwp_wait()able and daemon flags.
                 */
                ct->t_proc_flag |=
                    (t->t_proc_flag & (TP_TWAIT|TP_DAEMON));
                /*
                 * Keep track of the clone of curthread to
                 * post return values through lwp_setrval().
                 * Mark other threads for special treatment
                 * by lwp_rtt() / post_syscall().
                 */
                if (t == curthread)
                    clone = clwp;
                else
                    ct->t_flag |= T_FORKALL;
            } else {
                /*
                 * Replicate zombie lwps in the child.
                 */
                clep = kmem_zalloc(sizeof (*clep), KM_SLEEP);
                clep->le_lwpid = lep->le_lwpid;
                clep->le_start = lep->le_start;
                lwp_hash_in(cp, clep);
            }
        }
    }

    /*
     * Put new process in the parent's process contract, or put it
     * in a new one if there is an active process template.  Send a
     * fork event (if requested) to whatever contract the child is
     * a member of.  Fails if the parent has been SIGKILLed.
     */
    if (contract_process_fork(NULL, cp, p, B_TRUE) == NULL)
        goto forklwperr;

    /*
     * No fork failures occur beyond this point.
     */

    cp->p_lwpid = p->p_lwpid;
    if (!isfork1) {
        cp->p_lwpdaemon = p->p_lwpdaemon;
        cp->p_zombcnt = p->p_zombcnt;
        /*
         * If the parent's lwp ids have wrapped around, so have the
         * child's.
         */
        cp->p_flag |= p->p_flag & SLWPWRAP;
    }

    mutex_enter(&p->p_lock);
    corectl_path_hold(cp->p_corefile = p->p_corefile);
    corectl_content_hold(cp->p_content = p->p_content);
    mutex_exit(&p->p_lock);

    /*
     * Duplicate process context ops, if any.
     */
    if (p->p_pctx)
        forkpctx(p, cp);

#ifdef __sparc
    utrap_dup(p, cp);
#endif
    /*
     * If the child process has been marked to stop on exit
     * from this fork, arrange for all other lwps to stop in
     * sympathy with the active lwp.
     */
    if (PTOU(cp)->u_systrap &&
        prismember(&PTOU(cp)->u_exitmask, curthread->t_sysnum)) {
        mutex_enter(&cp->p_lock);
        t = cp->p_tlist;
        do {
            t->t_proc_flag |= TP_PRSTOP;
            aston(t);   /* so TP_PRSTOP will be seen */
        } while ((t = t->t_forw) != cp->p_tlist);
        mutex_exit(&cp->p_lock);
    }
    /*
     * If the parent process has been marked to stop on exit
     * from this fork, and its asynchronous-stop flag has not
     * been set, arrange for all other lwps to stop before
     * they return back to user level.
     */
    if (!(p->p_proc_flag & P_PR_ASYNC) && PTOU(p)->u_systrap &&
        prismember(&PTOU(p)->u_exitmask, curthread->t_sysnum)) {
        mutex_enter(&p->p_lock);
        t = p->p_tlist;
        do {
            t->t_proc_flag |= TP_PRSTOP;
            aston(t);   /* so TP_PRSTOP will be seen */
        } while ((t = t->t_forw) != p->p_tlist);
        mutex_exit(&p->p_lock);
    }

    if (PROC_IS_BRANDED(p))
        BROP(p)->b_lwp_setrval(clone, p->p_pid, 1);
    else
        lwp_setrval(clone, p->p_pid, 1);

    /* set return values for parent */
    r.r_val1 = (int)cp->p_pid;
    r.r_val2 = 0;

    /*
     * pool_barrier_exit() can now be called because the child process has:
     * - all identifying features cloned or set (p_pid, p_task, p_pool)
     * - all resource sets associated (p_tlist->*->t_cpupart, p_as->a_mset)
     * - any other fields set which are used in resource set binding.
     */
    mutex_enter(&p->p_lock);
    pool_barrier_exit();
    mutex_exit(&p->p_lock);

    mutex_enter(&pidlock);
    mutex_enter(&cp->p_lock);

    /*
     * Set flags telling the child what (not) to do on exit.
     */
    if (flags & FORK_NOSIGCHLD)
        cp->p_pidflag |= CLDNOSIGCHLD;
    if (flags & FORK_WAITPID)
        cp->p_pidflag |= CLDWAITPID;

    /*
     * Now that there are lwps and threads attached, add the new
     * process to the process group.
     */
    pgjoin(cp, p->p_pgidp);
    cp->p_stat = SRUN;
    /*
     * We are now done with all the lwps in the child process.
     */
    t = cp->p_tlist;
    do {
        /*
         * Set the lwp_suspend()ed lwps running.
         * They will suspend properly at syscall exit.
         */
        if (t->t_proc_flag & TP_HOLDLWP)
            lwp_create_done(t);
        else {
            /* set TS_CREATE to allow continuelwps() to work */
            thread_lock(t);
            ASSERT(t->t_state == TS_STOPPED &&
                !(t->t_schedflag & (TS_CREATE|TS_CSTART)));
            t->t_schedflag |= TS_CREATE;
            thread_unlock(t);
        }
    } while ((t = t->t_forw) != cp->p_tlist);
    mutex_exit(&cp->p_lock);

    if (isvfork) {
        CPU_STATS_ADDQ(CPU, sys, sysvfork, 1);
        mutex_enter(&p->p_lock);
        p->p_flag |= SVFWAIT;
        curthread->t_flag |= T_VFPARENT;
        DTRACE_PROC1(create, proc_t *, cp);
        cv_broadcast(&pr_pid_cv[p->p_slot]);    /* inform /proc */
        mutex_exit(&p->p_lock);
        /*
         * Grab child's p_lock before dropping pidlock to ensure
         * the process will not disappear before we set it running.
         */
        mutex_enter(&cp->p_lock);
        mutex_exit(&pidlock);
        sigdefault(cp);
        continuelwps(cp);
        mutex_exit(&cp->p_lock);
    } else {
        CPU_STATS_ADDQ(CPU, sys, sysfork, 1);
        DTRACE_PROC1(create, proc_t *, cp);
        /*
         * It is CL_FORKRET's job to drop pidlock.
         * If we do it here, the process could be set running
         * and disappear before CL_FORKRET() is called.
         */
        CL_FORKRET(curthread, cp->p_tlist);
        ASSERT(MUTEX_NOT_HELD(&pidlock));
    }

    return (r.r_vals);

forklwperr:
    if (isvfork) {
        if (avl_numnodes(&p->p_wpage) != 0) {
            /* restore watchpoints to parent */
            as = p->p_as;
            AS_LOCK_ENTER(as, &as->a_lock,
                RW_WRITER);
            as->a_wpage = p->p_wpage;
            avl_create(&p->p_wpage, wp_compare,
                sizeof (struct watched_page),
                offsetof(struct watched_page, wp_link));
            as_setwatch(as);
            AS_LOCK_EXIT(as, &as->a_lock);
        }
    } else {
        if (cp->p_segacct)
            shmexit(cp);
        as = cp->p_as;
        cp->p_as = &kas;
        as_free(as);
    }

    if (cp->p_lwpdir) {
        for (i = 0, ldp = cp->p_lwpdir; i < cp->p_lwpdir_sz; i++, ldp++)
            if ((lep = ldp->ld_entry) != NULL)
                kmem_free(lep, sizeof (*lep));
        kmem_free(cp->p_lwpdir,
            cp->p_lwpdir_sz * sizeof (*cp->p_lwpdir));
    }
    cp->p_lwpdir = NULL;
    cp->p_lwpfree = NULL;
    cp->p_lwpdir_sz = 0;

    if (cp->p_tidhash)
        kmem_free(cp->p_tidhash,
            cp->p_tidhash_sz * sizeof (*cp->p_tidhash));
    cp->p_tidhash = NULL;
    cp->p_tidhash_sz = 0;

    forklwp_fail(cp);
    fork_fail(cp);
    rctl_set_free(cp->p_rctls);
    mutex_enter(&pidlock);

    /*
     * Detach failed child from task.
     */
    mutex_enter(&cp->p_lock);
    tk = cp->p_task;
    task_detach(cp);
    ASSERT(cp->p_pool->pool_ref > 0);
    atomic_add_32(&cp->p_pool->pool_ref, -1);
    mutex_exit(&cp->p_lock);

    orphpp = &p->p_orphan;
    while (*orphpp != cp)
        orphpp = &(*orphpp)->p_nextorph;
    *orphpp = cp->p_nextorph;
    if (p->p_child == cp)
        p->p_child = cp->p_sibling;
    if (cp->p_sibling)
        cp->p_sibling->p_psibling = cp->p_psibling;
    if (cp->p_psibling)
        cp->p_psibling->p_sibling = cp->p_sibling;
    pid_exit(cp);
    mutex_exit(&pidlock);

    task_rele(tk);

    mutex_enter(&p->p_lock);
    pool_barrier_exit();
    continuelwps(p);
    mutex_exit(&p->p_lock);
    error = EAGAIN;
forkerr:
    return ((int64_t)set_errno(error));
}

/*
 * Free allocated resources from getproc() if a fork failed.
 */
static void
fork_fail(proc_t *cp)
{
    uf_info_t *fip = P_FINFO(cp);

    fcnt_add(fip, -1);
    sigdelq(cp, NULL, 0);

    mutex_enter(&pidlock);
    upcount_dec(crgetruid(cp->p_cred), crgetzoneid(cp->p_cred));
    mutex_exit(&pidlock);

    /*
     * single threaded, so no locking needed here
     */
    crfree(cp->p_cred);

    kmem_free(fip->fi_list, fip->fi_nfiles * sizeof (uf_entry_t));

    VN_RELE(PTOU(curproc)->u_cdir);
    if (PTOU(curproc)->u_rdir)
        VN_RELE(PTOU(curproc)->u_rdir);
    if (cp->p_exec)
        VN_RELE(cp->p_exec);
    if (cp->p_execdir)
        VN_RELE(cp->p_execdir);
    if (PTOU(curproc)->u_cwd)
        refstr_rele(PTOU(curproc)->u_cwd);
}

/*
 * Clean up the lwps already created for this child process.
 * The fork failed while duplicating all the lwps of the parent
 * and those lwps already created must be freed.
 * This process is invisible to the rest of the system,
 * so we don't need to hold p->p_lock to protect the list.
 */
static void
forklwp_fail(proc_t *p)
{
    kthread_t *t;
    task_t *tk;

    while ((t = p->p_tlist) != NULL) {
        /*
         * First remove the lwp from the process's p_tlist.
         */
        if (t != t->t_forw)
            p->p_tlist = t->t_forw;
        else
            p->p_tlist = NULL;
        p->p_lwpcnt--;
        t->t_forw->t_back = t->t_back;
        t->t_back->t_forw = t->t_forw;

        tk = p->p_task;
        mutex_enter(&p->p_zone->zone_nlwps_lock);
        tk->tk_nlwps--;
        tk->tk_proj->kpj_nlwps--;
        p->p_zone->zone_nlwps--;
        mutex_exit(&p->p_zone->zone_nlwps_lock);

        ASSERT(t->t_schedctl == NULL);

        if (t->t_door != NULL) {
            kmem_free(t->t_door, sizeof (door_data_t));
            t->t_door = NULL;
        }
        lwp_ctmpl_clear(ttolwp(t));

        /*
         * Remove the thread from the all threads list.
         * We need to hold pidlock for this.
         */
        mutex_enter(&pidlock);
        t->t_next->t_prev = t->t_prev;
        t->t_prev->t_next = t->t_next;
        CL_EXIT(t); /* tell the scheduler that we're exiting */
        cv_broadcast(&t->t_joincv); /* tell anyone in thread_join */
        mutex_exit(&pidlock);

        /*
         * Let the lgroup load averages know that this thread isn't
         * going to show up (i.e. un-do what was done on behalf of
         * this thread by the earlier lgrp_move_thread()).
         */
        kpreempt_disable();
        lgrp_move_thread(t, NULL, 1);
        kpreempt_enable();

        /*
         * The thread was created TS_STOPPED.
         * We change it to TS_FREE to avoid an
         * ASSERT() panic in thread_free().
         */
        t->t_state = TS_FREE;
        thread_rele(t);
        thread_free(t);
    }
}

extern struct as kas;

/*
 * fork a kernel process.
 */
int
newproc(void (*pc)(), caddr_t arg, id_t cid, int pri, struct contract **ct)
{
    proc_t *p;
    struct user *up;
    klwp_t *lwp;
    cont_process_t *ctp = NULL;
    rctl_entity_p_t e;

    ASSERT(!(cid == syscid && ct != NULL));
    if (cid == syscid) {
        rctl_alloc_gp_t *init_gp;
        rctl_set_t *init_set;

        if (getproc(&p, 1) < 0)
            return (EAGAIN);

        p->p_flag |= SNOWAIT;
        p->p_exec = NULL;
        p->p_execdir = NULL;

        init_set = rctl_set_create();
        init_gp = rctl_set_init_prealloc(RCENTITY_PROCESS);

        /*
         * kernel processes do not inherit /proc tracing flags.
         */
        sigemptyset(&p->p_sigmask);
        premptyset(&p->p_fltmask);
        up = PTOU(p);
        up->u_systrap = 0;
        premptyset(&(up->u_entrymask));
        premptyset(&(up->u_exitmask));
        mutex_enter(&p->p_lock);
        e.rcep_p.proc = p;
        e.rcep_t = RCENTITY_PROCESS;
        p->p_rctls = rctl_set_init(RCENTITY_PROCESS, p, &e, init_set,
            init_gp);
        mutex_exit(&p->p_lock);

        rctl_prealloc_destroy(init_gp);
    } else  {
        rctl_alloc_gp_t *init_gp, *default_gp;
        rctl_set_t *init_set;
        task_t *tk, *tk_old;

        if (getproc(&p, 0) < 0)
            return (EAGAIN);
        /*
         * init creates a new task, distinct from the task
         * containing kernel "processes".
         */
        tk = task_create(0, p->p_zone);
        mutex_enter(&tk->tk_zone->zone_nlwps_lock);
        tk->tk_proj->kpj_ntasks++;
        mutex_exit(&tk->tk_zone->zone_nlwps_lock);

        default_gp = rctl_rlimit_set_prealloc(RLIM_NLIMITS);
        init_gp = rctl_set_init_prealloc(RCENTITY_PROCESS);
        init_set = rctl_set_create();

        mutex_enter(&pidlock);
        mutex_enter(&p->p_lock);
        tk_old = p->p_task; /* switch to new task */

        task_detach(p);
        task_begin(tk, p);
        mutex_exit(&pidlock);

        e.rcep_p.proc = p;
        e.rcep_t = RCENTITY_PROCESS;
        p->p_rctls = rctl_set_init(RCENTITY_PROCESS, p, &e, init_set,
            init_gp);
        rctlproc_default_init(p, default_gp);
        mutex_exit(&p->p_lock);

        task_rele(tk_old);
        rctl_prealloc_destroy(default_gp);
        rctl_prealloc_destroy(init_gp);
    }

    p->p_as = &kas;

    if ((lwp = lwp_create(pc, arg, 0, p, TS_STOPPED, pri,
        &curthread->t_hold, cid, 1)) == NULL) {
        task_t *tk;
        fork_fail(p);
        mutex_enter(&pidlock);
        mutex_enter(&p->p_lock);
        tk = p->p_task;
        task_detach(p);
        ASSERT(p->p_pool->pool_ref > 0);
        atomic_add_32(&p->p_pool->pool_ref, -1);
        mutex_exit(&p->p_lock);
        pid_exit(p);
        mutex_exit(&pidlock);
        task_rele(tk);

        return (EAGAIN);
    }

    if (cid != syscid) {
        ctp = contract_process_fork(sys_process_tmpl, p, curproc,
            B_FALSE);
        ASSERT(ctp != NULL);
        if (ct != NULL)
            *ct = &ctp->conp_contract;
    }

    p->p_lwpid = 1;
    mutex_enter(&pidlock);
    pgjoin(p, curproc->p_pgidp);
    p->p_stat = SRUN;
    mutex_enter(&p->p_lock);
    lwptot(lwp)->t_proc_flag &= ~TP_HOLDLWP;
    lwp_create_done(lwptot(lwp));
    mutex_exit(&p->p_lock);
    mutex_exit(&pidlock);
    return (0);
}

/*
 * create a child proc struct.
 */
static int
getproc(proc_t **cpp, int kernel)
{
    proc_t      *pp, *cp;
    pid_t       newpid;
    struct user *uarea;
    extern uint_t   nproc;
    struct cred *cr;
    uid_t       ruid;
    zoneid_t    zoneid;

    if (!page_mem_avail(tune.t_minarmem))
        return (-1);
    if (zone_status_get(curproc->p_zone) >= ZONE_IS_SHUTTING_DOWN)
        return (-1);    /* no point in starting new processes */

    pp = curproc;
    cp = kmem_cache_alloc(process_cache, KM_SLEEP);
    bzero(cp, sizeof (proc_t));

    /*
     * Make proc entry for child process
     */
    mutex_init(&cp->p_splock, NULL, MUTEX_DEFAULT, NULL);
    mutex_init(&cp->p_crlock, NULL, MUTEX_DEFAULT, NULL);
    mutex_init(&cp->p_pflock, NULL, MUTEX_DEFAULT, NULL);
#if defined(__x86)
    mutex_init(&cp->p_ldtlock, NULL, MUTEX_DEFAULT, NULL);
#endif
    mutex_init(&cp->p_maplock, NULL, MUTEX_DEFAULT, NULL);
    cp->p_stat = SIDL;
    cp->p_mstart = gethrtime();
    /*
     * p_zone must be set before we call pid_allocate since the process
     * will be visible after that and code such as prfind_zone will
     * look at the p_zone field.
     */
    cp->p_zone = pp->p_zone;
    cp->p_t1_lgrpid = LGRP_NONE;
    cp->p_tr_lgrpid = LGRP_NONE;

    if ((newpid = pid_allocate(cp, PID_ALLOC_PROC)) == -1) {
        if (nproc == v.v_proc) {
            CPU_STATS_ADDQ(CPU, sys, procovf, 1);
            cmn_err(CE_WARN, "out of processes");
        }
        goto bad;
    }

    /*
     * If not privileged make sure that this user hasn't exceeded
     * v.v_maxup processes, and that users collectively haven't
     * exceeded v.v_maxupttl processes.
     */
    mutex_enter(&pidlock);
    ASSERT(nproc < v.v_proc);   /* otherwise how'd we get our pid? */
    cr = CRED();
    ruid = crgetruid(cr);
    zoneid = crgetzoneid(cr);
    if (nproc >= v.v_maxup &&   /* short-circuit; usually false */
        (nproc >= v.v_maxupttl ||
        upcount_get(ruid, zoneid) >= v.v_maxup) &&
        secpolicy_newproc(cr) != 0) {
        mutex_exit(&pidlock);
        zcmn_err(zoneid, CE_NOTE,
            "out of per-user processes for uid %d", ruid);
        goto bad;
    }

    /*
     * Everything is cool, put the new proc on the active process list.
     * It is already on the pid list and in /proc.
     * Increment the per uid process count (upcount).
     */
    nproc++;
    upcount_inc(ruid, zoneid);

    cp->p_next = practive;
    practive->p_prev = cp;
    practive = cp;

    cp->p_ignore = pp->p_ignore;
    cp->p_siginfo = pp->p_siginfo;
    cp->p_flag = pp->p_flag & (SJCTL|SNOWAIT|SNOCD);
    cp->p_sessp = pp->p_sessp;
    sess_hold(pp);
    cp->p_exec = pp->p_exec;
    cp->p_execdir = pp->p_execdir;
    cp->p_brand = pp->p_brand;
    if (PROC_IS_BRANDED(pp))
        BROP(pp)->b_copy_procdata(cp, pp);

    cp->p_bssbase = pp->p_bssbase;
    cp->p_brkbase = pp->p_brkbase;
    cp->p_brksize = pp->p_brksize;
    cp->p_brkpageszc = pp->p_brkpageszc;
    cp->p_stksize = pp->p_stksize;
    cp->p_stkpageszc = pp->p_stkpageszc;
    cp->p_stkprot = pp->p_stkprot;
    cp->p_datprot = pp->p_datprot;
    cp->p_usrstack = pp->p_usrstack;
    cp->p_model = pp->p_model;
    cp->p_ppid = pp->p_pid;
    cp->p_ancpid = pp->p_pid;
    cp->p_portcnt = pp->p_portcnt;

    /*
     * Initialize watchpoint structures
     */
    avl_create(&cp->p_warea, wa_compare, sizeof (struct watched_area),
        offsetof(struct watched_area, wa_link));

    /*
     * Initialize immediate resource control values.
     */
    cp->p_stk_ctl = pp->p_stk_ctl;
    cp->p_fsz_ctl = pp->p_fsz_ctl;
    cp->p_vmem_ctl = pp->p_vmem_ctl;
    cp->p_fno_ctl = pp->p_fno_ctl;

    /*
     * Link up to parent-child-sibling chain.  No need to lock
     * in general since only a call to freeproc() (done by the
     * same parent as newproc()) diddles with the child chain.
     */
    cp->p_sibling = pp->p_child;
    if (pp->p_child)
        pp->p_child->p_psibling = cp;

    cp->p_parent = pp;
    pp->p_child = cp;

    cp->p_child_ns = NULL;
    cp->p_sibling_ns = NULL;

    cp->p_nextorph = pp->p_orphan;
    cp->p_nextofkin = pp;
    pp->p_orphan = cp;

    /*
     * Inherit profiling state; do not inherit REALPROF profiling state.
     */
    cp->p_prof = pp->p_prof;
    cp->p_rprof_cyclic = CYCLIC_NONE;

    /*
     * Inherit pool pointer from the parent.  Kernel processes are
     * always bound to the default pool.
     */
    mutex_enter(&pp->p_lock);
    if (kernel) {
        cp->p_pool = pool_default;
        cp->p_flag |= SSYS;
    } else {
        cp->p_pool = pp->p_pool;
    }
    atomic_add_32(&cp->p_pool->pool_ref, 1);
    mutex_exit(&pp->p_lock);

    /*
     * Add the child process to the current task.  Kernel processes
     * are always attached to task0.
     */
    mutex_enter(&cp->p_lock);
    if (kernel)
        task_attach(task0p, cp);
    else
        task_attach(pp->p_task, cp);
    mutex_exit(&cp->p_lock);
    mutex_exit(&pidlock);

    avl_create(&cp->p_ct_held, contract_compar, sizeof (contract_t),
        offsetof(contract_t, ct_ctlist));

    /*
     * Duplicate any audit information kept in the process table
     */
    if (audit_active)   /* copy audit data to cp */
        audit_newproc(cp);

    crhold(cp->p_cred = cr);

    /*
     * Bump up the counts on the file structures pointed at by the
     * parent's file table since the child will point at them too.
     */
    fcnt_add(P_FINFO(pp), 1);

    VN_HOLD(PTOU(pp)->u_cdir);
    if (PTOU(pp)->u_rdir)
        VN_HOLD(PTOU(pp)->u_rdir);
    if (PTOU(pp)->u_cwd)
        refstr_hold(PTOU(pp)->u_cwd);

    /*
     * copy the parent's uarea.
     */
    uarea = PTOU(cp);
    bcopy(PTOU(pp), uarea, sizeof (*uarea));
    flist_fork(P_FINFO(pp), P_FINFO(cp));

    gethrestime(&uarea->u_start);
    uarea->u_ticks = lbolt;
    uarea->u_mem = rm_asrss(pp->p_as);
    uarea->u_acflag = AFORK;

    /*
     * If inherit-on-fork, copy /proc tracing flags to child.
     */
    if ((pp->p_proc_flag & P_PR_FORK) != 0) {
        cp->p_proc_flag |= pp->p_proc_flag & (P_PR_TRACE|P_PR_FORK);
        cp->p_sigmask = pp->p_sigmask;
        cp->p_fltmask = pp->p_fltmask;
    } else {
        sigemptyset(&cp->p_sigmask);
        premptyset(&cp->p_fltmask);
        uarea->u_systrap = 0;
        premptyset(&uarea->u_entrymask);
        premptyset(&uarea->u_exitmask);
    }
    /*
     * If microstate accounting is being inherited, mark child
     */
    if ((pp->p_flag & SMSFORK) != 0)
        cp->p_flag |= pp->p_flag & (SMSFORK|SMSACCT);

    /*
     * Inherit fixalignment flag from the parent
     */
    cp->p_fixalignment = pp->p_fixalignment;

    if (cp->p_exec)
        VN_HOLD(cp->p_exec);
    if (cp->p_execdir)
        VN_HOLD(cp->p_execdir);
    *cpp = cp;
    return (0);

bad:
    ASSERT(MUTEX_NOT_HELD(&pidlock));

    mutex_destroy(&cp->p_crlock);
    mutex_destroy(&cp->p_pflock);
#if defined(__x86)
    mutex_destroy(&cp->p_ldtlock);
#endif
    if (newpid != -1) {
        proc_entry_free(cp->p_pidp);
        (void) pid_rele(cp->p_pidp);
    }
    kmem_cache_free(process_cache, cp);

    /*
     * We most likely got into this situation because some process is
     * forking out of control.  As punishment, put it to sleep for a
     * bit so it can't eat the machine alive.  Sleep interval is chosen
     * to allow no more than one fork failure per cpu per clock tick
     * on average (yes, I just made this up).  This has two desirable
     * properties: (1) it sets a constant limit on the fork failure
     * rate, and (2) the busier the system is, the harsher the penalty
     * for abusing it becomes.
     */
    INCR_COUNT(&fork_fail_pending, &pidlock);
    delay(fork_fail_pending / ncpus + 1);
    DECR_COUNT(&fork_fail_pending, &pidlock);

    return (-1); /* out of memory or proc slots */
}

/*
 * Release virtual memory.
 * In the case of vfork(), the child was given exclusive access to its
 * parent's address space.  The parent is waiting in vfwait() for the
 * child to release its exclusive claim via relvm().
 */
void
relvm()
{
    proc_t *p = curproc;

    ASSERT((unsigned)p->p_lwpcnt <= 1);

    prrelvm();  /* inform /proc */

    if (p->p_flag & SVFORK) {
        proc_t *pp = p->p_parent;
        /*
         * The child process is either exec'ing or exit'ing.
         * The child is now separated from the parent's address
         * space.  The parent process is made dispatchable.
         *
         * This is a delicate locking maneuver, involving
         * both the parent's p_lock and the child's p_lock.
         * As soon as the SVFORK flag is turned off, the
         * parent is free to run, but it must not run until
         * we wake it up using its p_cv because it might
         * exit and we would be referencing invalid memory.
         * Therefore, we hold the parent with its p_lock
         * while protecting our p_flags with our own p_lock.
         */
try_again:
        mutex_enter(&p->p_lock);    /* grab child's lock first */
        prbarrier(p);       /* make sure /proc is blocked out */
        mutex_enter(&pp->p_lock);

        /*
         * Check if parent is locked by /proc.
         */
        if (pp->p_proc_flag & P_PR_LOCK) {
            /*
             * Delay until /proc is done with the parent.
             * We must drop our (the child's) p->p_lock, wait
             * via prbarrier() on the parent, then start over.
             */
            mutex_exit(&p->p_lock);
            prbarrier(pp);
            mutex_exit(&pp->p_lock);
            goto try_again;
        }
        p->p_flag &= ~SVFORK;
        kpreempt_disable();
        p->p_as = &kas;

        /*
         * notify hat of change in thread's address space
         */
        hat_thread_exit(curthread);
        kpreempt_enable();

        /*
         * child sizes are copied back to parent because
         * child may have grown.
         */
        pp->p_brkbase = p->p_brkbase;
        pp->p_brksize = p->p_brksize;
        pp->p_stksize = p->p_stksize;
        /*
         * The parent is no longer waiting for the vfork()d child.
         * Restore the parent's watched pages, if any.  This is
         * safe because we know the parent is not locked by /proc
         */
        pp->p_flag &= ~SVFWAIT;
        if (avl_numnodes(&pp->p_wpage) != 0) {
            pp->p_as->a_wpage = pp->p_wpage;
            avl_create(&pp->p_wpage, wp_compare,
                sizeof (struct watched_page),
                offsetof(struct watched_page, wp_link));
        }
        cv_signal(&pp->p_cv);
        mutex_exit(&pp->p_lock);
        mutex_exit(&p->p_lock);
    } else {
        if (p->p_as != &kas) {
            struct as *as;

            if (p->p_segacct)
                shmexit(p);

            /*
             * We grab p_lock for the benefit of /proc
             */
            kpreempt_disable();
            mutex_enter(&p->p_lock);
            prbarrier(p);   /* make sure /proc is blocked out */
            as = p->p_as;
            p->p_as = &kas;
            mutex_exit(&p->p_lock);

            /*
             * notify hat of change in thread's address space
             */
            hat_thread_exit(curthread);
            kpreempt_enable();

            as_free(as);
            p->p_tr_lgrpid = LGRP_NONE;
        }
    }
}

/*
 * Wait for child to exec or exit.
 * Called by parent of vfork'ed process.
 * See important comments in relvm(), above.
 */
void
vfwait(pid_t pid)
{
    int signalled = 0;
    proc_t *pp = ttoproc(curthread);
    proc_t *cp;

    /*
     * Wait for child to exec or exit.
     */
    for (;;) {
        mutex_enter(&pidlock);
        cp = prfind(pid);
        if (cp == NULL || cp->p_parent != pp) {
            /*
             * Child has exit()ed.
             */
            mutex_exit(&pidlock);
            break;
        }
        /*
         * Grab the child's p_lock before releasing pidlock.
         * Otherwise, the child could exit and we would be
         * referencing invalid memory.
         */
        mutex_enter(&cp->p_lock);
        mutex_exit(&pidlock);
        if (!(cp->p_flag & SVFORK)) {
            /*
             * Child has exec()ed or is exit()ing.
             */
            mutex_exit(&cp->p_lock);
            break;
        }
        mutex_enter(&pp->p_lock);
        mutex_exit(&cp->p_lock);
        /*
         * We might be waked up spuriously from the cv_wait().
         * We have to do the whole operation over again to be
         * sure the child's SVFORK flag really is turned off.
         * We cannot make reference to the child because it can
         * exit before we return and we would be referencing
         * invalid memory.
         *
         * Because this is potentially a very long-term wait,
         * we call cv_wait_sig() (for its jobcontrol and /proc
         * side-effects) unless there is a current signal, in
         * which case we use cv_wait() because we cannot return
         * from this function until the child has released the
         * address space.  Calling cv_wait_sig() with a current
         * signal would lead to an indefinite loop here because
         * cv_wait_sig() returns immediately in this case.
         */
        if (signalled)
            cv_wait(&pp->p_cv, &pp->p_lock);
        else
            signalled = !cv_wait_sig(&pp->p_cv, &pp->p_lock);
        mutex_exit(&pp->p_lock);
    }

    /* restore watchpoints to parent */
    if (pr_watch_active(pp)) {
        struct as *as = pp->p_as;
        AS_LOCK_ENTER(as, &as->a_lock, RW_WRITER);
        as_setwatch(as);
        AS_LOCK_EXIT(as, &as->a_lock);
    }

    mutex_enter(&pp->p_lock);
    prbarrier(pp);  /* barrier against /proc locking */
    continuelwps(pp);
    mutex_exit(&pp->p_lock);
}