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38 * @(#)kern_exit.c 8.7 (Berkeley) 2/12/94
39 * $FreeBSD: src/sys/kern/kern_exit.c,v 1.92.2.11 2003/01/13 22:51:16 dillon Exp $
40 * $DragonFly: src/sys/kern/kern_exit.c,v 1.91 2008/05/18 20:02:02 nth Exp $
43 #include "opt_compat.h"
44 #include "opt_ktrace.h"
46 #include <sys/param.h>
47 #include <sys/systm.h>
48 #include <sys/sysproto.h>
49 #include <sys/kernel.h>
50 #include <sys/malloc.h>
52 #include <sys/ktrace.h>
53 #include <sys/pioctl.h>
56 #include <sys/vnode.h>
57 #include <sys/resourcevar.h>
58 #include <sys/signalvar.h>
59 #include <sys/taskqueue.h>
60 #include <sys/ptrace.h>
61 #include <sys/acct.h> /* for acct_process() function prototype */
62 #include <sys/filedesc.h>
67 #include <sys/kern_syscall.h>
68 #include <sys/upcall.h>
70 #include <sys/unistd.h>
71 #include <sys/eventhandler.h>
72 #include <sys/dsched.h>
75 #include <vm/vm_param.h>
78 #include <vm/vm_map.h>
79 #include <vm/vm_extern.h>
82 #include <sys/refcount.h>
83 #include <sys/thread2.h>
84 #include <sys/sysref2.h>
85 #include <sys/mplock2.h>
87 static void reaplwps(void *context, int dummy);
88 static void reaplwp(struct lwp *lp);
89 static void killlwps(struct lwp *lp);
91 static MALLOC_DEFINE(M_ATEXIT, "atexit", "atexit callback");
92 static MALLOC_DEFINE(M_ZOMBIE, "zombie", "zombie proc status");
94 static struct lwkt_token deadlwp_token = LWKT_TOKEN_INITIALIZER(deadlwp_token);
97 * callout list for things to do at exit time
100 exitlist_fn function;
101 TAILQ_ENTRY(exitlist) next;
104 TAILQ_HEAD(exit_list_head, exitlist);
105 static struct exit_list_head exit_list = TAILQ_HEAD_INITIALIZER(exit_list);
110 struct task *deadlwp_task[MAXCPU];
111 struct lwplist deadlwp_list[MAXCPU];
117 * SYS_EXIT_ARGS(int rval)
120 sys_exit(struct exit_args *uap)
122 exit1(W_EXITCODE(uap->rval, 0));
128 * Death of a lwp or process with optional bells and whistles.
133 sys_extexit(struct extexit_args *uap)
135 struct proc *p = curproc;
139 action = EXTEXIT_ACTION(uap->how);
140 who = EXTEXIT_WHO(uap->how);
142 /* Check parameters before we might perform some action */
155 error = copyout(&uap->status, uap->addr, sizeof(uap->status));
163 lwkt_gettoken(&p->p_token);
168 * Be sure only to perform a simple lwp exit if there is at
169 * least one more lwp in the proc, which will call exit1()
170 * later, otherwise the proc will be an UNDEAD and not even a
173 if (p->p_nthreads > 1) {
174 lwp_exit(0); /* called w/ p_token held */
177 /* else last lwp in proc: do the real thing */
179 default: /* to help gcc */
181 lwkt_reltoken(&p->p_token);
182 exit1(W_EXITCODE(uap->status, 0));
187 lwkt_reltoken(&p->p_token); /* safety */
191 * Kill all lwps associated with the current process except the
192 * current lwp. Return an error if we race another thread trying to
193 * do the same thing and lose the race.
195 * If forexec is non-zero the current thread and process flags are
196 * cleaned up so they can be reused.
199 killalllwps(int forexec)
201 struct lwp *lp = curthread->td_lwp;
202 struct proc *p = lp->lwp_proc;
205 * Interlock against P_WEXIT. Only one of the process's thread
206 * is allowed to do the master exit.
208 if (p->p_flag & P_WEXIT)
210 p->p_flag |= P_WEXIT;
213 * Interlock with LWP_WEXIT and kill any remaining LWPs
215 lp->lwp_flag |= LWP_WEXIT;
216 if (p->p_nthreads > 1)
220 * If doing this for an exec, clean up the remaining thread
221 * (us) for continuing operation after all the other threads
225 lp->lwp_flag &= ~LWP_WEXIT;
226 p->p_flag &= ~P_WEXIT;
232 * Kill all LWPs except the current one. Do not try to signal
233 * LWPs which have exited on their own or have already been
237 killlwps(struct lwp *lp)
239 struct proc *p = lp->lwp_proc;
243 * Kill the remaining LWPs. We must send the signal before setting
244 * LWP_WEXIT. The setting of WEXIT is optional but helps reduce
245 * races. tlp must be held across the call as it might block and
246 * allow the target lwp to rip itself out from under our loop.
248 FOREACH_LWP_IN_PROC(tlp, p) {
250 if ((tlp->lwp_flag & LWP_WEXIT) == 0) {
251 lwpsignal(p, tlp, SIGKILL);
252 tlp->lwp_flag |= LWP_WEXIT;
258 * Wait for everything to clear out.
260 while (p->p_nthreads > 1) {
261 tsleep(&p->p_nthreads, 0, "killlwps", 0);
266 * Exit: deallocate address space and other resources, change proc state
267 * to zombie, and unlink proc from allproc and parent's lists. Save exit
268 * status and rusage for wait(). Check for child processes and orphan them.
273 struct thread *td = curthread;
274 struct proc *p = td->td_proc;
275 struct lwp *lp = td->td_lwp;
282 lwkt_gettoken(&p->p_token);
285 kprintf("init died (signal %d, exit %d)\n",
286 WTERMSIG(rv), WEXITSTATUS(rv));
287 panic("Going nowhere without my init!");
289 varsymset_clean(&p->p_varsymset);
290 lockuninit(&p->p_varsymset.vx_lock);
292 * Kill all lwps associated with the current process, return an
293 * error if we race another thread trying to do the same thing
296 error = killalllwps(0);
302 caps_exit(lp->lwp_thread);
304 /* are we a task leader? */
305 if (p == p->p_leader) {
306 struct kill_args killArgs;
307 killArgs.signum = SIGKILL;
310 killArgs.pid = q->p_pid;
312 * The interface for kill is better
313 * than the internal signal
320 tsleep((caddr_t)p, 0, "exit1", 0);
326 STOPEVENT(p, S_EXIT, rv);
327 wakeup(&p->p_stype); /* Wakeup anyone in procfs' PIOCWAIT */
330 * Check if any loadable modules need anything done at process exit.
331 * e.g. SYSV IPC stuff
332 * XXX what if one of these generates an error?
335 EVENTHANDLER_INVOKE(process_exit, p);
338 * XXX: imho, the eventhandler stuff is much cleaner than this.
339 * Maybe we should move everything to use eventhandler.
341 TAILQ_FOREACH(ep, &exit_list, next)
344 if (p->p_flag & P_PROFIL)
347 * If parent is waiting for us to exit or exec,
348 * P_PPWAIT is set; we will wakeup the parent below.
350 p->p_flag &= ~(P_TRACED | P_PPWAIT);
351 SIGEMPTYSET(p->p_siglist);
352 SIGEMPTYSET(lp->lwp_siglist);
353 if (timevalisset(&p->p_realtimer.it_value))
354 callout_stop(&p->p_ithandle);
357 * Reset any sigio structures pointing to us as a result of
358 * F_SETOWN with our pid.
360 funsetownlst(&p->p_sigiolst);
363 * Close open files and release open-file table.
368 if(p->p_leader->p_peers) {
370 while(q->p_peers != p)
372 q->p_peers = p->p_peers;
373 wakeup((caddr_t)p->p_leader);
377 * XXX Shutdown SYSV semaphores
381 KKASSERT(p->p_numposixlocks == 0);
383 /* The next two chunks should probably be moved to vmspace_exit. */
387 * Release upcalls associated with this process
393 * Clean up data related to virtual kernel operation. Clean up
394 * any vkernel context related to the current lwp now so we can
398 vkernel_lwp_exit(lp);
403 * Release user portion of address space.
404 * This releases references to vnodes,
405 * which could cause I/O if the file has been unlinked.
406 * Need to do this early enough that we can still sleep.
407 * Can't free the entire vmspace as the kernel stack
408 * may be mapped within that space also.
410 * Processes sharing the same vmspace may exit in one order, and
411 * get cleaned up by vmspace_exit() in a different order. The
412 * last exiting process to reach this point releases as much of
413 * the environment as it can, and the last process cleaned up
414 * by vmspace_exit() (which decrements exitingcnt) cleans up the
417 vmspace_exitbump(vm);
418 sysref_put(&vm->vm_sysref);
420 if (SESS_LEADER(p)) {
421 struct session *sp = p->p_session;
425 * We are the controlling process. Signal the
426 * foreground process group, drain the controlling
427 * terminal, and revoke access to the controlling
430 * NOTE: while waiting for the process group to exit
431 * it is possible that one of the processes in the
432 * group will revoke the tty, so the ttyclosesession()
433 * function will re-check sp->s_ttyvp.
435 if (sp->s_ttyp && (sp->s_ttyp->t_session == sp)) {
436 if (sp->s_ttyp->t_pgrp)
437 pgsignal(sp->s_ttyp->t_pgrp, SIGHUP, 1);
439 ttyclosesession(sp, 1); /* also revoke */
442 * Release the tty. If someone has it open via
443 * /dev/tty then close it (since they no longer can
444 * once we've NULL'd it out).
446 ttyclosesession(sp, 0);
449 * s_ttyp is not zero'd; we use this to indicate
450 * that the session once had a controlling terminal.
451 * (for logging and informational purposes)
456 fixjobc(p, p->p_pgrp, 0);
457 (void)acct_process(p);
463 ktrdestroy(&p->p_tracenode);
467 * Release reference to text vnode
469 if ((vtmp = p->p_textvp) != NULL) {
474 /* Release namecache handle to text file */
475 if (p->p_textnch.ncp)
476 cache_drop(&p->p_textnch);
479 * Move the process to the zombie list. This will block
480 * until the process p_lock count reaches 0. The process will
481 * not be reaped until TDF_EXITING is set by cpu_thread_exit(),
482 * which is called from cpu_proc_exit().
484 proc_move_allproc_zombie(p);
487 * Reparent all of this process's children to the init process.
488 * We must hold initproc->p_token in order to mess with
489 * initproc->p_children. We already hold p->p_token (to remove
490 * the children from our list).
492 q = LIST_FIRST(&p->p_children);
494 lwkt_gettoken(&initproc->p_token);
496 nq = LIST_NEXT(q, p_sibling);
497 LIST_REMOVE(q, p_sibling);
498 LIST_INSERT_HEAD(&initproc->p_children, q, p_sibling);
499 q->p_pptr = initproc;
500 q->p_sigparent = SIGCHLD;
502 * Traced processes are killed
503 * since their existence means someone is screwing up.
505 if (q->p_flag & P_TRACED) {
506 q->p_flag &= ~P_TRACED;
511 lwkt_reltoken(&initproc->p_token);
516 * Save exit status and final rusage info, adding in child rusage
517 * info and self times.
519 calcru_proc(p, &p->p_ru);
520 ruadd(&p->p_ru, &p->p_cru);
523 * notify interested parties of our demise.
525 KNOTE(&p->p_klist, NOTE_EXIT);
528 * Notify parent that we're gone. If parent has the PS_NOCLDWAIT
529 * flag set, notify process 1 instead (and hope it will handle
532 if (p->p_pptr->p_sigacts->ps_flag & PS_NOCLDWAIT) {
533 struct proc *pp = p->p_pptr;
536 proc_reparent(p, initproc);
539 * If this was the last child of our parent, notify
540 * parent, so in case he was wait(2)ing, he will
541 * continue. This function interlocks with pptr->p_token.
543 if (LIST_EMPTY(&pp->p_children))
548 /* lwkt_gettoken(&proc_token); */
551 if (p->p_sigparent && q != initproc) {
552 ksignal(q, p->p_sigparent);
558 /* lwkt_reltoken(&proc_token); */
559 /* NOTE: p->p_pptr can get ripped out */
561 * cpu_exit is responsible for clearing curproc, since
562 * it is heavily integrated with the thread/switching sequence.
564 * Other substructures are freed from wait().
569 * Release the current user process designation on the process so
570 * the userland scheduler can work in someone else.
572 p->p_usched->release_curproc(lp);
575 * Finally, call machine-dependent code to release as many of the
576 * lwp's resources as we can and halt execution of this thread.
582 * Eventually called by every exiting LWP
584 * p->p_token must be held. mplock may be held and will be released.
587 lwp_exit(int masterexit)
589 struct thread *td = curthread;
590 struct lwp *lp = td->td_lwp;
591 struct proc *p = lp->lwp_proc;
594 * lwp_exit() may be called without setting LWP_WEXIT, so
595 * make sure it is set here.
597 ASSERT_LWKT_TOKEN_HELD(&p->p_token);
598 lp->lwp_flag |= LWP_WEXIT;
601 * Clean up any virtualization
604 vkernel_lwp_exit(lp);
607 * Clean up select/poll support
609 kqueue_terminate(&lp->lwp_kqueue);
612 * Clean up any syscall-cached ucred
615 crfree(td->td_ucred);
620 * Nobody actually wakes us when the lock
621 * count reaches zero, so just wait one tick.
623 while (lp->lwp_lock > 0)
624 tsleep(lp, 0, "lwpexit", 1);
626 /* Hand down resource usage to our proc */
627 ruadd(&p->p_ru, &lp->lwp_ru);
630 * If we don't hold the process until the LWP is reaped wait*()
631 * may try to dispose of its vmspace before all the LWPs have
632 * actually terminated.
637 * Do any remaining work that might block on us. We should be
638 * coded such that further blocking is ok after decrementing
639 * p_nthreads but don't take the chance.
641 dsched_exit_thread(td);
642 biosched_done(curthread);
645 * We have to use the reaper for all the LWPs except the one doing
646 * the master exit. The LWP doing the master exit can just be
647 * left on p_lwps and the process reaper will deal with it
648 * synchronously, which is much faster.
650 * Wakeup anyone waiting on p_nthreads to drop to 1 or 0.
652 if (masterexit == 0) {
653 lwp_rb_tree_RB_REMOVE(&p->p_lwp_tree, lp);
655 if (p->p_nthreads <= 1)
656 wakeup(&p->p_nthreads);
657 lwkt_gettoken(&deadlwp_token);
658 LIST_INSERT_HEAD(&deadlwp_list[mycpuid], lp, u.lwp_reap_entry);
659 taskqueue_enqueue(taskqueue_thread[mycpuid],
660 deadlwp_task[mycpuid]);
661 lwkt_reltoken(&deadlwp_token);
664 if (p->p_nthreads <= 1)
665 wakeup(&p->p_nthreads);
669 * Release p_token. The mp_token may also be held and we depend on
670 * the lwkt_switch() code to clean it up.
672 lwkt_reltoken(&p->p_token);
677 * Wait until a lwp is completely dead.
679 * If the thread is still executing, which can't be waited upon,
680 * return failure. The caller is responsible of waiting a little
681 * bit and checking again.
684 * while (!lwp_wait(lp))
685 * tsleep(lp, 0, "lwpwait", 1);
688 lwp_wait(struct lwp *lp)
690 struct thread *td = lp->lwp_thread;;
692 KKASSERT(lwkt_preempted_proc() != lp);
694 while (lp->lwp_lock > 0)
695 tsleep(lp, 0, "lwpwait1", 1);
700 * The lwp's thread may still be in the middle
701 * of switching away, we can't rip its stack out from
702 * under it until TDF_EXITING is set and both
703 * TDF_RUNNING and TDF_PREEMPT_LOCK are clear.
704 * TDF_PREEMPT_LOCK must be checked because TDF_RUNNING
705 * will be cleared temporarily if a thread gets
708 * YYY no wakeup occurs, so we simply return failure
709 * and let the caller deal with sleeping and calling
712 if ((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
713 TDF_EXITING|TDF_RUNQ)) != TDF_EXITING) {
716 KASSERT((td->td_flags & TDF_TSLEEPQ) == 0,
717 ("lwp_wait: td %p (%s) still on sleep queue", td, td->td_comm));
722 * Release the resources associated with a lwp.
723 * The lwp must be completely dead.
726 lwp_dispose(struct lwp *lp)
728 struct thread *td = lp->lwp_thread;;
730 KKASSERT(lwkt_preempted_proc() != lp);
731 KKASSERT(td->td_refs == 0);
732 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|TDF_EXITING)) ==
740 lp->lwp_thread = NULL;
741 lwkt_free_thread(td);
750 sys_wait4(struct wait_args *uap)
752 struct rusage rusage;
755 error = kern_wait(uap->pid, (uap->status ? &status : NULL),
756 uap->options, (uap->rusage ? &rusage : NULL),
757 &uap->sysmsg_result);
759 if (error == 0 && uap->status)
760 error = copyout(&status, uap->status, sizeof(*uap->status));
761 if (error == 0 && uap->rusage)
762 error = copyout(&rusage, uap->rusage, sizeof(*uap->rusage));
769 * wait_args(int pid, int *status, int options, struct rusage *rusage)
774 kern_wait(pid_t pid, int *status, int options, struct rusage *rusage, int *res)
776 struct thread *td = curthread;
778 struct proc *q = td->td_proc;
786 if (options &~ (WUNTRACED|WNOHANG|WCONTINUED|WLINUXCLONE))
789 lwkt_gettoken(&q->p_token);
792 * All sorts of things can change due to blocking so we have to loop
793 * all the way back up here.
795 * The problem is that if a process group is stopped and the parent
796 * is doing a wait*(..., WUNTRACED, ...), it will see the STOP
797 * of the child and then stop itself when it tries to return from the
798 * system call. When the process group is resumed the parent will
799 * then get the STOP status even though the child has now resumed
800 * (a followup wait*() will get the CONT status).
802 * Previously the CONT would overwrite the STOP because the tstop
803 * was handled within tsleep(), and the parent would only see
804 * the CONT when both are stopped and continued together. This little
805 * two-line hack restores this effect.
807 while (q->p_stat == SSTOP)
812 LIST_FOREACH(p, &q->p_children, p_sibling) {
813 if (pid != WAIT_ANY &&
814 p->p_pid != pid && p->p_pgid != -pid) {
819 * This special case handles a kthread spawned by linux_clone
820 * (see linux_misc.c). The linux_wait4 and linux_waitpid
821 * functions need to be able to distinguish between waiting
822 * on a process and waiting on a thread. It is a thread if
823 * p_sigparent is not SIGCHLD, and the WLINUXCLONE option
824 * signifies we want to wait for threads and not processes.
826 if ((p->p_sigparent != SIGCHLD) ^
827 ((options & WLINUXCLONE) != 0)) {
832 if (p->p_stat == SZOMB) {
834 * We may go into SZOMB with threads still present.
835 * We must wait for them to exit before we can reap
836 * the master thread, otherwise we may race reaping
837 * non-master threads.
839 lwkt_gettoken(&p->p_token);
840 while (p->p_nthreads > 0) {
841 tsleep(&p->p_nthreads, 0, "lwpzomb", hz);
845 * Reap any LWPs left in p->p_lwps. This is usually
846 * just the last LWP. This must be done before
847 * we loop on p_lock since the lwps hold a ref on
848 * it as a vmspace interlock.
850 * Once that is accomplished p_nthreads had better
853 while ((lp = RB_ROOT(&p->p_lwp_tree)) != NULL) {
854 lwp_rb_tree_RB_REMOVE(&p->p_lwp_tree, lp);
857 KKASSERT(p->p_nthreads == 0);
858 lwkt_reltoken(&p->p_token);
861 * Don't do anything really bad until all references
862 * to the process go away. This may include other
863 * LWPs which are still in the process of being
864 * reaped. We can't just pull the rug out from under
865 * them because they may still be using the VM space.
867 * Certain kernel facilities such as /proc will also
868 * put a hold on the process for short periods of
872 tsleep(p, 0, "reap3", hz);
874 /* Take care of our return values. */
876 p->p_usched->heuristic_exiting(td->td_lwp, p);
879 *status = p->p_xstat;
883 * If we got the child via a ptrace 'attach',
884 * we need to give it back to the old parent.
886 if (p->p_oppid && (t = pfind(p->p_oppid)) != NULL) {
897 * Unlink the proc from its process group so that
898 * the following operations won't lead to an
899 * inconsistent state for processes running down
902 KKASSERT(p->p_lock == 0);
903 proc_remove_zombie(p);
907 ruadd(&q->p_cru, &p->p_ru);
910 * Decrement the count of procs running with this uid.
912 chgproccnt(p->p_ucred->cr_ruidinfo, -1, 0);
915 * Free up credentials.
921 * Remove unused arguments
925 if (pa && refcount_release(&pa->ar_ref)) {
932 if (ps && refcount_release(&ps->ps_refcnt)) {
933 kfree(ps, M_SUBPROC);
943 if (p->p_stat == SSTOP && (p->p_flag & P_WAITED) == 0 &&
944 (p->p_flag & P_TRACED || options & WUNTRACED)) {
945 p->p_flag |= P_WAITED;
948 p->p_usched->heuristic_exiting(td->td_lwp, p);
950 *status = W_STOPCODE(p->p_xstat);
951 /* Zero rusage so we get something consistent. */
953 bzero(rusage, sizeof(rusage));
957 if (options & WCONTINUED && (p->p_flag & P_CONTINUED)) {
959 p->p_usched->heuristic_exiting(td->td_lwp, p);
960 p->p_flag &= ~P_CONTINUED;
972 if (options & WNOHANG) {
979 * Wait for signal - interlocked using q->p_token.
981 error = tsleep(q, PCATCH, "wait", 0);
984 lwkt_reltoken(&q->p_token);
991 * Make process 'parent' the new parent of process 'child'.
993 * p_children/p_sibling requires the parent's token, and
994 * changing pptr requires the child's token, so we have to
995 * get three tokens to do this operation.
998 proc_reparent(struct proc *child, struct proc *parent)
1000 struct proc *opp = child->p_pptr;
1006 lwkt_gettoken(&opp->p_token);
1007 lwkt_gettoken(&child->p_token);
1008 lwkt_gettoken(&parent->p_token);
1009 KKASSERT(child->p_pptr == opp);
1010 LIST_REMOVE(child, p_sibling);
1011 LIST_INSERT_HEAD(&parent->p_children, child, p_sibling);
1012 child->p_pptr = parent;
1013 lwkt_reltoken(&parent->p_token);
1014 lwkt_reltoken(&child->p_token);
1015 lwkt_reltoken(&opp->p_token);
1021 * The next two functions are to handle adding/deleting items on the
1025 * Take the arguments given and put them onto the exit callout list,
1026 * However first make sure that it's not already there.
1027 * returns 0 on success.
1031 at_exit(exitlist_fn function)
1033 struct exitlist *ep;
1036 /* Be noisy if the programmer has lost track of things */
1037 if (rm_at_exit(function))
1038 kprintf("WARNING: exit callout entry (%p) already present\n",
1041 ep = kmalloc(sizeof(*ep), M_ATEXIT, M_NOWAIT);
1044 ep->function = function;
1045 TAILQ_INSERT_TAIL(&exit_list, ep, next);
1050 * Scan the exit callout list for the given item and remove it.
1051 * Returns the number of items removed (0 or 1)
1054 rm_at_exit(exitlist_fn function)
1056 struct exitlist *ep;
1058 TAILQ_FOREACH(ep, &exit_list, next) {
1059 if (ep->function == function) {
1060 TAILQ_REMOVE(&exit_list, ep, next);
1061 kfree(ep, M_ATEXIT);
1069 * LWP reaper related code.
1072 reaplwps(void *context, int dummy)
1074 struct lwplist *lwplist = context;
1077 lwkt_gettoken(&deadlwp_token);
1078 while ((lp = LIST_FIRST(lwplist))) {
1079 LIST_REMOVE(lp, u.lwp_reap_entry);
1082 lwkt_reltoken(&deadlwp_token);
1086 reaplwp(struct lwp *lp)
1088 while (lwp_wait(lp) == 0)
1089 tsleep(lp, 0, "lwpreap", 1);
1098 for (cpu = 0; cpu < ncpus; cpu++) {
1099 LIST_INIT(&deadlwp_list[cpu]);
1100 deadlwp_task[cpu] = kmalloc(sizeof(*deadlwp_task[cpu]), M_DEVBUF, M_WAITOK);
1101 TASK_INIT(deadlwp_task[cpu], 0, reaplwps, &deadlwp_list[cpu]);
1105 SYSINIT(deadlwpinit, SI_SUB_CONFIGURE, SI_ORDER_ANY, deadlwp_init, NULL);