Add precautions so that threads won't race to exit1() and get stuck there.

[dragonfly.git] / sys / kern / kern_exit.c

/*
 * 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_exit.c 8.7 (Berkeley) 2/12/94
 * $FreeBSD: src/sys/kern/kern_exit.c,v 1.92.2.11 2003/01/13 22:51:16 dillon Exp $
 * $DragonFly: src/sys/kern/kern_exit.c,v 1.79 2007/03/12 21:05:48 corecode Exp $
 */

#include "opt_compat.h"
#include "opt_ktrace.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/sysproto.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/proc.h>
#include <sys/ktrace.h>
#include <sys/pioctl.h>
#include <sys/tty.h>
#include <sys/wait.h>
#include <sys/vnode.h>
#include <sys/resourcevar.h>
#include <sys/signalvar.h>
#include <sys/taskqueue.h>
#include <sys/ptrace.h>
#include <sys/acct.h>           /* for acct_process() function prototype */
#include <sys/filedesc.h>
#include <sys/shm.h>
#include <sys/sem.h>
#include <sys/aio.h>
#include <sys/jail.h>
#include <sys/kern_syscall.h>
#include <sys/upcall.h>
#include <sys/caps.h>
#include <sys/unistd.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <sys/lock.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
#include <vm/vm_zone.h>
#include <vm/vm_extern.h>
#include <sys/user.h>

#include <sys/thread2.h>

static MALLOC_DEFINE(M_ATEXIT, "atexit", "atexit callback");
static MALLOC_DEFINE(M_ZOMBIE, "zombie", "zombie proc status");

/*
 * callout list for things to do at exit time
 */
struct exitlist {
        exitlist_fn function;
        TAILQ_ENTRY(exitlist) next;
};

TAILQ_HEAD(exit_list_head, exitlist);
static struct exit_list_head exit_list = TAILQ_HEAD_INITIALIZER(exit_list);

/*
 * LWP reaper data
 */
struct task *deadlwp_task[MAXCPU];
struct lwplist deadlwp_list[MAXCPU];

/*
 * exit --
 *      Death of process.
 *
 * SYS_EXIT_ARGS(int rval)
 */
int
sys_exit(struct exit_args *uap)
{
        exit1(W_EXITCODE(uap->rval, 0));
        /* NOTREACHED */
}

/*
 * Extended exit --
 *      Death of a lwp or process with optional bells and whistles.
 */
int
sys_extexit(struct extexit_args *uap)
{
        int action, who;
        int error;

        action = EXTEXIT_ACTION(uap->how);
        who = EXTEXIT_WHO(uap->how);

        /* Check parameters before we might perform some action */
        switch (who) {
        case EXTEXIT_PROC:
        case EXTEXIT_LWP:
                break;

        default:
                return (EINVAL);
        }

        switch (action) {
        case EXTEXIT_SIMPLE:
                break;

        case EXTEXIT_SETINT:
                error = copyout(&uap->status, uap->addr, sizeof(uap->status));
                if (error)
                        return (error);
                break;

        default:
                return (EINVAL);
        }

        switch (who) {
        case EXTEXIT_LWP:
                /*
                 * Be sure only to perform a simple lwp exit if there is at
                 * least one more lwp in the proc, which will call exit1()
                 * later, otherwise the proc will be an UNDEAD and not even a
                 * SZOMB!
                 */
                if (curproc->p_nthreads > 1)
                        lwp_exit();
                /* else last lwp in proc:  do the real thing */
                /* FALLTHROUGH */

        default:        /* to help gcc */
        case EXTEXIT_PROC:
                exit1(W_EXITCODE(uap->status, 0));
                /* NOTREACHED */
        }

        /* NOTREACHED */
}

void
killlwps(struct lwp *lp)
{
        struct proc *p = lp->lwp_proc;
        struct lwp *tlp;

        KKASSERT((lp->lwp_flag & LWP_WEXIT) == 0);

        FOREACH_LWP_IN_PROC(tlp, p) {
                if (tlp == lp)
                        continue;       /* don't kill the current lwp */
                tlp->lwp_flag |= LWP_WEXIT;
                lwp_signotify(tlp);
        }

        while (p->p_nthreads > 1) {
                if (bootverbose)
                        kprintf("killlwps: waiting for %d lwps of pid %d to die\n",
                                p->p_nthreads - 1, p->p_pid);
                tsleep(&p->p_nthreads, 0, "killlwps", hz);
        }
}

/*
 * Exit: deallocate address space and other resources, change proc state
 * to zombie, and unlink proc from allproc and parent's lists.  Save exit
 * status and rusage for wait().  Check for child processes and orphan them.
 */
void
exit1(int rv)
{
        struct thread *td = curthread;
        struct proc *p = td->td_proc;
        struct lwp *lp = td->td_lwp;
        struct proc *q, *nq;
        struct vmspace *vm;
        struct vnode *vtmp;
        struct exitlist *ep;

        if (p->p_pid == 1) {
                kprintf("init died (signal %d, exit %d)\n",
                    WTERMSIG(rv), WEXITSTATUS(rv));
                panic("Going nowhere without my init!");
        }

        /*
         * Kill all other threads if there are any.
         *
         * If some other thread initiated our exit, do so.
         */
        if (lp->lwp_flag & LWP_WEXIT) {
                KKASSERT(p->p_nthreads > 1);
                lwp_exit();
        }
        if (p->p_nthreads > 1)
                killlwps(lp);

        caps_exit(lp->lwp_thread);
        aio_proc_rundown(p);

        /* are we a task leader? */
        if(p == p->p_leader) {
                struct kill_args killArgs;
                killArgs.signum = SIGKILL;
                q = p->p_peers;
                while(q) {
                        killArgs.pid = q->p_pid;
                        /*
                         * The interface for kill is better
                         * than the internal signal
                         */
                        sys_kill(&killArgs);
                        nq = q;
                        q = q->p_peers;
                }
                while (p->p_peers) 
                  tsleep((caddr_t)p, 0, "exit1", 0);
        } 

#ifdef PGINPROF
        vmsizmon();
#endif
        STOPEVENT(p, S_EXIT, rv);
        wakeup(&p->p_stype);    /* Wakeup anyone in procfs' PIOCWAIT */

        /* 
         * Check if any loadable modules need anything done at process exit.
         * e.g. SYSV IPC stuff
         * XXX what if one of these generates an error?
         */
        TAILQ_FOREACH(ep, &exit_list, next) 
                (*ep->function)(td);

        if (p->p_flag & P_PROFIL)
                stopprofclock(p);
        /*
         * If parent is waiting for us to exit or exec,
         * P_PPWAIT is set; we will wakeup the parent below.
         */
        p->p_flag &= ~(P_TRACED | P_PPWAIT);
        p->p_flag |= P_WEXIT;
        SIGEMPTYSET(p->p_siglist);
        SIGEMPTYSET(lp->lwp_siglist);
        if (timevalisset(&p->p_realtimer.it_value))
                callout_stop(&p->p_ithandle);

        /*
         * Reset any sigio structures pointing to us as a result of
         * F_SETOWN with our pid.
         */
        funsetownlst(&p->p_sigiolst);

        /*
         * Close open files and release open-file table.
         * This may block!
         */
        fdfree(p);
        p->p_fd = NULL;

        if(p->p_leader->p_peers) {
                q = p->p_leader;
                while(q->p_peers != p)
                        q = q->p_peers;
                q->p_peers = p->p_peers;
                wakeup((caddr_t)p->p_leader);
        }

        /*
         * XXX Shutdown SYSV semaphores
         */
        semexit(p);

        KKASSERT(p->p_numposixlocks == 0);

        /* The next two chunks should probably be moved to vmspace_exit. */
        vm = p->p_vmspace;

        /*
         * Release upcalls associated with this process
         */
        if (vm->vm_upcalls)
                upc_release(vm, lp);

        /* clean up data related to virtual kernel operation */
        if (p->p_vkernel)
                vkernel_exit(p);

        /*
         * Release user portion of address space.
         * This releases references to vnodes,
         * which could cause I/O if the file has been unlinked.
         * Need to do this early enough that we can still sleep.
         * Can't free the entire vmspace as the kernel stack
         * may be mapped within that space also.
         *
         * Processes sharing the same vmspace may exit in one order, and
         * get cleaned up by vmspace_exit() in a different order.  The
         * last exiting process to reach this point releases as much of
         * the environment as it can, and the last process cleaned up
         * by vmspace_exit() (which decrements exitingcnt) cleans up the
         * remainder.
         */
        ++vm->vm_exitingcnt;
        if (--vm->vm_refcnt == 0) {
                shmexit(vm);
                pmap_remove_pages(vmspace_pmap(vm), VM_MIN_USER_ADDRESS,
                                  VM_MAX_USER_ADDRESS);
                vm_map_remove(&vm->vm_map, VM_MIN_USER_ADDRESS,
                              VM_MAX_USER_ADDRESS);
        }

        if (SESS_LEADER(p)) {
                struct session *sp = p->p_session;
                struct vnode *vp;

                if (sp->s_ttyvp) {
                        /*
                         * We are the controlling process.  Signal the 
                         * foreground process group, drain the controlling
                         * terminal, and revoke access to the controlling
                         * terminal.
                         *
                         * NOTE: while waiting for the process group to exit
                         * it is possible that one of the processes in the
                         * group will revoke the tty, so we have to recheck.
                         */
                        if (sp->s_ttyp && (sp->s_ttyp->t_session == sp)) {
                                if (sp->s_ttyp->t_pgrp)
                                        pgsignal(sp->s_ttyp->t_pgrp, SIGHUP, 1);
                                (void) ttywait(sp->s_ttyp);
                                /*
                                 * The tty could have been revoked
                                 * if we blocked.
                                 */
                                if ((vp = sp->s_ttyvp) != NULL) {
                                        ttyclosesession(sp, 0);
                                        vx_lock(vp);
                                        VOP_REVOKE(vp, REVOKEALL);
                                        vx_unlock(vp);
                                        vrele(vp);      /* s_ttyvp ref */
                                }
                        }
                        /*
                         * Release the tty.  If someone has it open via
                         * /dev/tty then close it (since they no longer can
                         * once we've NULL'd it out).
                         */
                        if (sp->s_ttyvp)
                                ttyclosesession(sp, 1);
                        /*
                         * s_ttyp is not zero'd; we use this to indicate
                         * that the session once had a controlling terminal.
                         * (for logging and informational purposes)
                         */
                }
                sp->s_leader = NULL;
        }
        fixjobc(p, p->p_pgrp, 0);
        (void)acct_process(p);
#ifdef KTRACE
        /*
         * release trace file
         */
        if (p->p_tracenode)
                ktrdestroy(&p->p_tracenode);
        p->p_traceflag = 0;
#endif
        /*
         * Release reference to text vnode
         */
        if ((vtmp = p->p_textvp) != NULL) {
                p->p_textvp = NULL;
                vrele(vtmp);
        }

        /*
         * Move the process to the zombie list.  This will block
         * until the process p_lock count reaches 0.  The process will
         * not be reaped until TDF_EXITING is set by cpu_thread_exit(),
         * which is called from cpu_proc_exit().
         */
        proc_move_allproc_zombie(p);

        q = LIST_FIRST(&p->p_children);
        if (q)          /* only need this if any child is S_ZOMB */
                wakeup((caddr_t) initproc);
        for (; q != 0; q = nq) {
                nq = LIST_NEXT(q, p_sibling);
                LIST_REMOVE(q, p_sibling);
                LIST_INSERT_HEAD(&initproc->p_children, q, p_sibling);
                q->p_pptr = initproc;
                q->p_sigparent = SIGCHLD;
                /*
                 * Traced processes are killed
                 * since their existence means someone is screwing up.
                 */
                if (q->p_flag & P_TRACED) {
                        q->p_flag &= ~P_TRACED;
                        ksignal(q, SIGKILL);
                }
        }

        /*
         * Save exit status and final rusage info, adding in child rusage
         * info and self times.
         */
        p->p_xstat = rv;
        calcru_proc(p, &p->p_ru);
        ruadd(&p->p_ru, &p->p_cru);

        /*
         * notify interested parties of our demise.
         */
        KNOTE(&p->p_klist, NOTE_EXIT);

        /*
         * Notify parent that we're gone.  If parent has the PS_NOCLDWAIT
         * flag set, notify process 1 instead (and hope it will handle
         * this situation).
         */
        if (p->p_pptr->p_sigacts->ps_flag & PS_NOCLDWAIT) {
                struct proc *pp = p->p_pptr;
                proc_reparent(p, initproc);
                /*
                 * If this was the last child of our parent, notify
                 * parent, so in case he was wait(2)ing, he will
                 * continue.
                 */
                if (LIST_EMPTY(&pp->p_children))
                        wakeup((caddr_t)pp);
        }

        if (p->p_sigparent && p->p_pptr != initproc) {
                ksignal(p->p_pptr, p->p_sigparent);
        } else {
                ksignal(p->p_pptr, SIGCHLD);
        }

        wakeup((caddr_t)p->p_pptr);
        /*
         * cpu_exit is responsible for clearing curproc, since
         * it is heavily integrated with the thread/switching sequence.
         *
         * Other substructures are freed from wait().
         */
        plimit_free(&p->p_limit);

        /*
         * Release the current user process designation on the process so
         * the userland scheduler can work in someone else.
         */
        p->p_usched->release_curproc(lp);

        /*
         * Finally, call machine-dependent code to release the remaining
         * resources including address space, the kernel stack and pcb.
         * The address space is released by "vmspace_free(p->p_vmspace)";
         * This is machine-dependent, as we may have to change stacks
         * or ensure that the current one isn't reallocated before we
         * finish.  cpu_exit will end with a call to cpu_switch(), finishing
         * our execution (pun intended).
         */
        lwp_exit();
}

void
lwp_exit(void)
{
        struct lwp *lp = curthread->td_lwp;
        struct proc *p = lp->lwp_proc;

        /*
         * Nobody actually wakes us when the lock
         * count reaches zero, so just wait one tick.
         */
        while (lp->lwp_lock > 0)
                tsleep(lp, 0, "lwpexit", 1);

        /* Hand down resource usage to our proc */
        ruadd(&p->p_ru, &lp->lwp_ru);

        --p->p_nthreads;
        LIST_REMOVE(lp, lwp_list);
        wakeup(&p->p_nthreads);
        LIST_INSERT_HEAD(&deadlwp_list[mycpuid], lp, lwp_list);
        taskqueue_enqueue(taskqueue_thread[mycpuid], deadlwp_task[mycpuid]);
        cpu_lwp_exit();
}

/*
 * Wait until a lwp is completely dead.
 *
 * If the thread is still executing, which can't be waited upon,
 * return failure.  The caller is responsible of waiting a little
 * bit and checking again.
 *
 * Suggested use:
 * while (!lwp_wait(lp))
 *      tsleep(lp, 0, "lwpwait", 1);
 */
static int
lwp_wait(struct lwp *lp)
{
        struct thread *td = lp->lwp_thread;;

        KKASSERT(lwkt_preempted_proc() != lp);

        while (lp->lwp_lock > 0)
                tsleep(lp, 0, "lwpwait1", 1);

        lwkt_wait_free(td);

        /*
         * The lwp's thread may still be in the middle
         * of switching away, we can't rip its stack out from
         * under it until TDF_EXITING is set and both
         * TDF_RUNNING and TDF_PREEMPT_LOCK are clear.
         * TDF_PREEMPT_LOCK must be checked because TDF_RUNNING
         * will be cleared temporarily if a thread gets
         * preempted.
         *
         * YYY no wakeup occurs, so we simply return failure
         * and let the caller deal with sleeping and calling
         * us again.
         */
        if ((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|TDF_EXITING)) !=
            TDF_EXITING)
                return (0);

        return (1);
}

/*
 * Release the resources associated with a lwp.
 * The lwp must be completely dead.
 */
void
lwp_dispose(struct lwp *lp)
{
        struct thread *td = lp->lwp_thread;;

        KKASSERT(lwkt_preempted_proc() != lp);
        KKASSERT(td->td_refs == 0);
        KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|TDF_EXITING)) ==
                 TDF_EXITING);

        if (td != NULL) {
                td->td_proc = NULL;
                td->td_lwp = NULL;
                lp->lwp_thread = NULL;
                lwkt_free_thread(td);
        }
        zfree(lwp_zone, lp);
}

int
sys_wait4(struct wait_args *uap)
{
        struct rusage rusage;
        int error, status;

        error = kern_wait(uap->pid, uap->status ? &status : NULL,
            uap->options, uap->rusage ? &rusage : NULL, &uap->sysmsg_fds[0]);

        if (error == 0 && uap->status)
                error = copyout(&status, uap->status, sizeof(*uap->status));
        if (error == 0 && uap->rusage)
                error = copyout(&rusage, uap->rusage, sizeof(*uap->rusage));
        return (error);
}

/*
 * wait1()
 *
 * wait_args(int pid, int *status, int options, struct rusage *rusage)
 */
int
kern_wait(pid_t pid, int *status, int options, struct rusage *rusage, int *res)
{
        struct thread *td = curthread;
        struct proc *q = td->td_proc;
        struct proc *p, *t;
        int nfound, error;

        if (pid == 0)
                pid = -q->p_pgid;
        if (options &~ (WUNTRACED|WNOHANG|WLINUXCLONE))
                return (EINVAL);
loop:
        /*
         * Hack for backwards compatibility with badly written user code.  
         * Or perhaps we have to do this anyway, it is unclear. XXX
         *
         * The problem is that if a process group is stopped and the parent
         * is doing a wait*(..., WUNTRACED, ...), it will see the STOP
         * of the child and then stop itself when it tries to return from the
         * system call.  When the process group is resumed the parent will
         * then get the STOP status even though the child has now resumed
         * (a followup wait*() will get the CONT status).
         *
         * Previously the CONT would overwrite the STOP because the tstop
         * was handled within tsleep(), and the parent would only see
         * the CONT when both are stopped and continued together.  This litte
         * two-line hack restores this effect.
         */
        while (q->p_stat == SSTOP)
            tstop();

        nfound = 0;
        LIST_FOREACH(p, &q->p_children, p_sibling) {
                if (pid != WAIT_ANY &&
                    p->p_pid != pid && p->p_pgid != -pid)
                        continue;

                /* This special case handles a kthread spawned by linux_clone 
                 * (see linux_misc.c).  The linux_wait4 and linux_waitpid 
                 * functions need to be able to distinguish between waiting
                 * on a process and waiting on a thread.  It is a thread if
                 * p_sigparent is not SIGCHLD, and the WLINUXCLONE option
                 * signifies we want to wait for threads and not processes.
                 */
                if ((p->p_sigparent != SIGCHLD) ^ 
                    ((options & WLINUXCLONE) != 0)) {
                        continue;
                }

                nfound++;
                if (p->p_stat == SZOMB) {
                        /*
                         * Other kernel threads may be in the middle of 
                         * accessing the proc.  For example, kern/kern_proc.c
                         * could be blocked writing proc data to a sysctl.
                         * At the moment, if this occurs, we are not woken
                         * up and rely on a one-second retry.
                         */
                        while (p->p_lock)
                                tsleep(p, 0, "reap3", hz);

                        /* scheduling hook for heuristic */
                        /* XXX no lwp available, we need a different heuristic */
                        /*
                        p->p_usched->heuristic_exiting(td->td_lwp, deadlp);
                        */

                        /* Take care of our return values. */
                        *res = p->p_pid;
                        if (status)
                                *status = p->p_xstat;
                        if (rusage)
                                *rusage = p->p_ru;
                        /*
                         * If we got the child via a ptrace 'attach',
                         * we need to give it back to the old parent.
                         */
                        if (p->p_oppid && (t = pfind(p->p_oppid))) {
                                p->p_oppid = 0;
                                proc_reparent(p, t);
                                ksignal(t, SIGCHLD);
                                wakeup((caddr_t)t);
                                return (0);
                        }
                        p->p_xstat = 0;
                        ruadd(&q->p_cru, &p->p_ru);

                        /*
                         * Decrement the count of procs running with this uid.
                         */
                        chgproccnt(p->p_ucred->cr_ruidinfo, -1, 0);

                        /*
                         * Free up credentials.
                         */
                        crfree(p->p_ucred);
                        p->p_ucred = NULL;

                        /*
                         * Remove unused arguments
                         */
                        if (p->p_args && --p->p_args->ar_ref == 0)
                                FREE(p->p_args, M_PARGS);

                        /*
                         * Finally finished with old proc entry.
                         * Unlink it from its process group and free it.
                         */
                        proc_remove_zombie(p);
                        leavepgrp(p);

                        if (--p->p_sigacts->ps_refcnt == 0) {
                                kfree(p->p_sigacts, M_SUBPROC);
                                p->p_sigacts = NULL;
                        }

                        vm_waitproc(p);
                        zfree(proc_zone, p);
                        nprocs--;
                        return (0);
                }
                if (p->p_stat == SSTOP && (p->p_flag & P_WAITED) == 0 &&
                    (p->p_flag & P_TRACED || options & WUNTRACED)) {
                        p->p_flag |= P_WAITED;

                        *res = p->p_pid;
                        if (status)
                                *status = W_STOPCODE(p->p_xstat);
                        /* Zero rusage so we get something consistent. */
                        if (rusage)
                                bzero(rusage, sizeof(rusage));
                        return (0);
                }
        }
        if (nfound == 0)
                return (ECHILD);
        if (options & WNOHANG) {
                *res = 0;
                return (0);
        }
        error = tsleep((caddr_t)q, PCATCH, "wait", 0);
        if (error)
                return (error);
        goto loop;
}

/*
 * make process 'parent' the new parent of process 'child'.
 */
void
proc_reparent(struct proc *child, struct proc *parent)
{

        if (child->p_pptr == parent)
                return;

        LIST_REMOVE(child, p_sibling);
        LIST_INSERT_HEAD(&parent->p_children, child, p_sibling);
        child->p_pptr = parent;
}

/*
 * The next two functions are to handle adding/deleting items on the
 * exit callout list
 * 
 * at_exit():
 * Take the arguments given and put them onto the exit callout list,
 * However first make sure that it's not already there.
 * returns 0 on success.
 */

int
at_exit(exitlist_fn function)
{
        struct exitlist *ep;

#ifdef INVARIANTS
        /* Be noisy if the programmer has lost track of things */
        if (rm_at_exit(function)) 
                kprintf("WARNING: exit callout entry (%p) already present\n",
                    function);
#endif
        ep = kmalloc(sizeof(*ep), M_ATEXIT, M_NOWAIT);
        if (ep == NULL)
                return (ENOMEM);
        ep->function = function;
        TAILQ_INSERT_TAIL(&exit_list, ep, next);
        return (0);
}

/*
 * Scan the exit callout list for the given item and remove it.
 * Returns the number of items removed (0 or 1)
 */
int
rm_at_exit(exitlist_fn function)
{
        struct exitlist *ep;

        TAILQ_FOREACH(ep, &exit_list, next) {
                if (ep->function == function) {
                        TAILQ_REMOVE(&exit_list, ep, next);
                        kfree(ep, M_ATEXIT);
                        return(1);
                }
        }       
        return (0);
}


/*
 * LWP reaper related code.
 */

static void
reaplwps(void *context, int dummy)
{
        struct lwplist *lwplist = context;
        struct lwp *lp;

        while ((lp = LIST_FIRST(lwplist))) {
                if (!lwp_wait(lp))
                        tsleep(lp, 0, "lwpreap", 1);
                LIST_REMOVE(lp, lwp_list);
                lwp_dispose(lp);
        }
}

static void
deadlwp_init(void)
{
        int cpu;

        for (cpu = 0; cpu < ncpus; cpu++) {
                LIST_INIT(&deadlwp_list[cpu]);
                deadlwp_task[cpu] = kmalloc(sizeof(*deadlwp_task[cpu]), M_DEVBUF, M_WAITOK);
                TASK_INIT(deadlwp_task[cpu], 0, reaplwps, &deadlwp_list[cpu]);
        }
}

SYSINIT(deadlwpinit, SI_SUB_CONFIGURE, SI_ORDER_ANY, deadlwp_init, NULL);