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34 * @(#)kern_fork.c 8.6 (Berkeley) 4/8/94
35 * $FreeBSD: src/sys/kern/kern_fork.c,v 1.72.2.14 2003/06/26 04:15:10 silby Exp $
38 #include "opt_ktrace.h"
40 #include <sys/param.h>
41 #include <sys/systm.h>
42 #include <sys/sysproto.h>
43 #include <sys/filedesc.h>
44 #include <sys/kernel.h>
45 #include <sys/sysctl.h>
46 #include <sys/malloc.h>
48 #include <sys/resourcevar.h>
49 #include <sys/vnode.h>
51 #include <sys/ktrace.h>
52 #include <sys/unistd.h>
58 #include <vm/vm_map.h>
59 #include <vm/vm_extern.h>
61 #include <sys/vmmeter.h>
62 #include <sys/refcount.h>
63 #include <sys/thread2.h>
64 #include <sys/signal2.h>
65 #include <sys/spinlock2.h>
67 #include <sys/dsched.h>
69 static MALLOC_DEFINE(M_ATFORK, "atfork", "atfork callback");
70 static MALLOC_DEFINE(M_REAPER, "reaper", "process reapers");
73 * These are the stuctures used to create a callout list for things to do
74 * when forking a process
78 TAILQ_ENTRY(forklist) next;
81 TAILQ_HEAD(forklist_head, forklist);
82 static struct forklist_head fork_list = TAILQ_HEAD_INITIALIZER(fork_list);
84 static struct lwp *lwp_fork(struct lwp *, struct proc *, int flags);
86 int forksleep; /* Place for fork1() to sleep on. */
89 * Red-Black tree support for LWPs
93 rb_lwp_compare(struct lwp *lp1, struct lwp *lp2)
95 if (lp1->lwp_tid < lp2->lwp_tid)
97 if (lp1->lwp_tid > lp2->lwp_tid)
102 RB_GENERATE2(lwp_rb_tree, lwp, u.lwp_rbnode, rb_lwp_compare, lwpid_t, lwp_tid);
108 sys_fork(struct fork_args *uap)
110 struct lwp *lp = curthread->td_lwp;
114 error = fork1(lp, RFFDG | RFPROC | RFPGLOCK, &p2);
117 start_forked_proc(lp, p2);
118 uap->sysmsg_fds[0] = p2->p_pid;
119 uap->sysmsg_fds[1] = 0;
126 * vfork() system call
129 sys_vfork(struct vfork_args *uap)
131 struct lwp *lp = curthread->td_lwp;
135 error = fork1(lp, RFFDG | RFPROC | RFPPWAIT | RFMEM | RFPGLOCK, &p2);
138 start_forked_proc(lp, p2);
139 uap->sysmsg_fds[0] = p2->p_pid;
140 uap->sysmsg_fds[1] = 0;
147 * Handle rforks. An rfork may (1) operate on the current process without
148 * creating a new, (2) create a new process that shared the current process's
149 * vmspace, signals, and/or descriptors, or (3) create a new process that does
150 * not share these things (normal fork).
152 * Note that we only call start_forked_proc() if a new process is actually
155 * rfork { int flags }
158 sys_rfork(struct rfork_args *uap)
160 struct lwp *lp = curthread->td_lwp;
164 if ((uap->flags & RFKERNELONLY) != 0)
167 error = fork1(lp, uap->flags | RFPGLOCK, &p2);
171 start_forked_proc(lp, p2);
172 uap->sysmsg_fds[0] = p2->p_pid;
173 uap->sysmsg_fds[1] = 0;
176 uap->sysmsg_fds[0] = 0;
177 uap->sysmsg_fds[1] = 0;
184 * Low level thread create used by pthreads.
187 sys_lwp_create(struct lwp_create_args *uap)
189 struct proc *p = curproc;
191 struct lwp_params params;
194 error = copyin(uap->params, ¶ms, sizeof(params));
198 lwkt_gettoken(&p->p_token);
199 plimit_lwp_fork(p); /* force exclusive access */
200 lp = lwp_fork(curthread->td_lwp, p, RFPROC);
201 error = cpu_prepare_lwp(lp, ¶ms);
204 if (params.lwp_tid1 != NULL &&
205 (error = copyout(&lp->lwp_tid, params.lwp_tid1, sizeof(lp->lwp_tid))))
207 if (params.lwp_tid2 != NULL &&
208 (error = copyout(&lp->lwp_tid, params.lwp_tid2, sizeof(lp->lwp_tid))))
212 * Now schedule the new lwp.
214 p->p_usched->resetpriority(lp);
216 lp->lwp_stat = LSRUN;
217 p->p_usched->setrunqueue(lp);
219 lwkt_reltoken(&p->p_token);
224 lwp_rb_tree_RB_REMOVE(&p->p_lwp_tree, lp);
226 /* lwp_dispose expects an exited lwp, and a held proc */
227 atomic_set_int(&lp->lwp_mpflags, LWP_MP_WEXIT);
228 lp->lwp_thread->td_flags |= TDF_EXITING;
229 lwkt_remove_tdallq(lp->lwp_thread);
231 biosched_done(lp->lwp_thread);
232 dsched_exit_thread(lp->lwp_thread);
234 lwkt_reltoken(&p->p_token);
239 int nprocs = 1; /* process 0 */
242 fork1(struct lwp *lp1, int flags, struct proc **procp)
244 struct proc *p1 = lp1->lwp_proc;
249 struct sysreaper *reap;
252 static int curfail = 0;
253 static struct timeval lastfail;
255 struct filedesc_to_leader *fdtol;
257 if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
260 lwkt_gettoken(&p1->p_token);
265 * Here we don't create a new process, but we divorce
266 * certain parts of a process from itself.
268 if ((flags & RFPROC) == 0) {
270 * This kind of stunt does not work anymore if
271 * there are native threads (lwps) running
273 if (p1->p_nthreads != 1) {
278 vm_fork(p1, 0, flags);
281 * Close all file descriptors.
283 if (flags & RFCFDG) {
284 struct filedesc *fdtmp;
290 * Unshare file descriptors (from parent.)
293 if (p1->p_fd->fd_refcnt > 1) {
294 struct filedesc *newfd;
295 error = fdcopy(p1, &newfd);
309 * Interlock against process group signal delivery. If signals
310 * are pending after the interlock is obtained we have to restart
311 * the system call to process the signals. If we don't the child
312 * can miss a pgsignal (such as ^C) sent during the fork.
314 * We can't use CURSIG() here because it will process any STOPs
315 * and cause the process group lock to be held indefinitely. If
316 * a STOP occurs, the fork will be restarted after the CONT.
319 if ((flags & RFPGLOCK) && (plkgrp = p1->p_pgrp) != NULL) {
321 lockmgr(&plkgrp->pg_lock, LK_SHARED);
322 if (CURSIG_NOBLOCK(lp1)) {
329 * Although process entries are dynamically created, we still keep
330 * a global limit on the maximum number we will create. Don't allow
331 * a nonprivileged user to use the last ten processes; don't let root
332 * exceed the limit. The variable nprocs is the current number of
333 * processes, maxproc is the limit.
335 uid = lp1->lwp_thread->td_ucred->cr_ruid;
336 if ((nprocs >= maxproc - 10 && uid != 0) || nprocs >= maxproc) {
337 if (ppsratecheck(&lastfail, &curfail, 1))
338 kprintf("maxproc limit exceeded by uid %d, please "
339 "see tuning(7) and login.conf(5).\n", uid);
340 tsleep(&forksleep, 0, "fork", hz / 2);
346 * Increment the nprocs resource before blocking can occur. There
347 * are hard-limits as to the number of processes that can run.
349 atomic_add_int(&nprocs, 1);
352 * Increment the count of procs running with this uid. Don't allow
353 * a nonprivileged user to exceed their current limit.
355 ok = chgproccnt(lp1->lwp_thread->td_ucred->cr_ruidinfo, 1,
356 (uid != 0) ? p1->p_rlimit[RLIMIT_NPROC].rlim_cur : 0);
359 * Back out the process count
361 atomic_add_int(&nprocs, -1);
362 if (ppsratecheck(&lastfail, &curfail, 1))
363 kprintf("maxproc limit exceeded by uid %d, please "
364 "see tuning(7) and login.conf(5).\n", uid);
365 tsleep(&forksleep, 0, "fork", hz / 2);
371 * Allocate a new process, don't get fancy: zero the structure.
373 p2 = kmalloc(sizeof(struct proc), M_PROC, M_WAITOK|M_ZERO);
376 * Core initialization. SIDL is a safety state that protects the
377 * partially initialized process once it starts getting hooked
378 * into system structures and becomes addressable.
380 * We must be sure to acquire p2->p_token as well, we must hold it
381 * once the process is on the allproc list to avoid things such
382 * as competing modifications to p_flags.
384 mycpu->gd_forkid += ncpus;
385 p2->p_forkid = mycpu->gd_forkid + mycpu->gd_cpuid;
386 p2->p_lasttid = -1; /* first tid will be 0 */
390 * NOTE: Process 0 will not have a reaper, but process 1 (init) and
391 * all other processes always will.
393 if ((reap = p1->p_reaper) != NULL) {
400 RB_INIT(&p2->p_lwp_tree);
401 spin_init(&p2->p_spin, "procfork1");
402 lwkt_token_init(&p2->p_token, "proc");
403 lwkt_gettoken(&p2->p_token);
406 * Setup linkage for kernel based threading XXX lwp. Also add the
407 * process to the allproclist.
409 * The process structure is addressable after this point.
411 if (flags & RFTHREAD) {
412 p2->p_peers = p1->p_peers;
414 p2->p_leader = p1->p_leader;
418 proc_add_allproc(p2);
421 * Initialize the section which is copied verbatim from the parent.
423 bcopy(&p1->p_startcopy, &p2->p_startcopy,
424 ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy));
427 * Duplicate sub-structures as needed. Increase reference counts
430 * NOTE: because we are now on the allproc list it is possible for
431 * other consumers to gain temporary references to p2
432 * (p2->p_lock can change).
434 if (p1->p_flags & P_PROFIL)
436 p2->p_ucred = crhold(lp1->lwp_thread->td_ucred);
438 if (jailed(p2->p_ucred))
439 p2->p_flags |= P_JAILED;
442 refcount_acquire(&p2->p_args->ar_ref);
444 p2->p_usched = p1->p_usched;
445 /* XXX: verify copy of the secondary iosched stuff */
448 if (flags & RFSIGSHARE) {
449 p2->p_sigacts = p1->p_sigacts;
450 refcount_acquire(&p2->p_sigacts->ps_refcnt);
452 p2->p_sigacts = kmalloc(sizeof(*p2->p_sigacts),
453 M_SUBPROC, M_WAITOK);
454 bcopy(p1->p_sigacts, p2->p_sigacts, sizeof(*p2->p_sigacts));
455 refcount_init(&p2->p_sigacts->ps_refcnt, 1);
457 if (flags & RFLINUXTHPN)
458 p2->p_sigparent = SIGUSR1;
460 p2->p_sigparent = SIGCHLD;
462 /* bump references to the text vnode (for procfs) */
463 p2->p_textvp = p1->p_textvp;
467 /* copy namecache handle to the text file */
468 if (p1->p_textnch.mount)
469 cache_copy(&p1->p_textnch, &p2->p_textnch);
472 * Handle file descriptors
474 if (flags & RFCFDG) {
475 p2->p_fd = fdinit(p1);
477 } else if (flags & RFFDG) {
478 error = fdcopy(p1, &p2->p_fd);
485 p2->p_fd = fdshare(p1);
486 if (p1->p_fdtol == NULL) {
487 p1->p_fdtol = filedesc_to_leader_alloc(NULL,
490 if ((flags & RFTHREAD) != 0) {
492 * Shared file descriptor table and
493 * shared process leaders.
496 fdtol->fdl_refcount++;
499 * Shared file descriptor table, and
500 * different process leaders
502 fdtol = filedesc_to_leader_alloc(p1->p_fdtol, p2);
506 p2->p_limit = plimit_fork(p1);
509 * Preserve some more flags in subprocess. P_PROFIL has already
512 p2->p_flags |= p1->p_flags & P_SUGID;
513 if (p1->p_session->s_ttyvp != NULL && (p1->p_flags & P_CONTROLT))
514 p2->p_flags |= P_CONTROLT;
515 if (flags & RFPPWAIT) {
516 p2->p_flags |= P_PPWAIT;
518 p1->p_upmap->invfork = 1;
523 * Inherit the virtual kernel structure (allows a virtual kernel
524 * to fork to simulate multiple cpus).
527 vkernel_inherit(p1, p2);
530 * Once we are on a pglist we may receive signals. XXX we might
531 * race a ^C being sent to the process group by not receiving it
532 * at all prior to this line.
535 lwkt_gettoken(&p1grp->pg_token);
536 LIST_INSERT_AFTER(p1, p2, p_pglist);
537 lwkt_reltoken(&p1grp->pg_token);
540 * Attach the new process to its parent.
542 * If RFNOWAIT is set, the newly created process becomes a child
543 * of the reaper (typically init). This effectively disassociates
544 * the child from the parent.
546 * Temporarily hold pptr for the RFNOWAIT case to avoid ripouts.
548 if (flags & RFNOWAIT) {
549 pptr = reaper_get(reap);
558 LIST_INIT(&p2->p_children);
560 lwkt_gettoken(&pptr->p_token);
561 LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
562 lwkt_reltoken(&pptr->p_token);
564 if (flags & RFNOWAIT)
567 varsymset_init(&p2->p_varsymset, &p1->p_varsymset);
568 callout_init_mp(&p2->p_ithandle);
572 * Copy traceflag and tracefile if enabled. If not inherited,
573 * these were zeroed above but we still could have a trace race
574 * so make sure p2's p_tracenode is NULL.
576 if ((p1->p_traceflag & KTRFAC_INHERIT) && p2->p_tracenode == NULL) {
577 p2->p_traceflag = p1->p_traceflag;
578 p2->p_tracenode = ktrinherit(p1->p_tracenode);
583 * This begins the section where we must prevent the parent
584 * from being swapped.
586 * Gets PRELE'd in the caller in start_forked_proc().
590 vm_fork(p1, p2, flags);
593 * Create the first lwp associated with the new proc.
594 * It will return via a different execution path later, directly
595 * into userland, after it was put on the runq by
596 * start_forked_proc().
598 lwp_fork(lp1, p2, flags);
600 if (flags == (RFFDG | RFPROC | RFPGLOCK)) {
601 mycpu->gd_cnt.v_forks++;
602 mycpu->gd_cnt.v_forkpages += p2->p_vmspace->vm_dsize +
603 p2->p_vmspace->vm_ssize;
604 } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM | RFPGLOCK)) {
605 mycpu->gd_cnt.v_vforks++;
606 mycpu->gd_cnt.v_vforkpages += p2->p_vmspace->vm_dsize +
607 p2->p_vmspace->vm_ssize;
608 } else if (p1 == &proc0) {
609 mycpu->gd_cnt.v_kthreads++;
610 mycpu->gd_cnt.v_kthreadpages += p2->p_vmspace->vm_dsize +
611 p2->p_vmspace->vm_ssize;
613 mycpu->gd_cnt.v_rforks++;
614 mycpu->gd_cnt.v_rforkpages += p2->p_vmspace->vm_dsize +
615 p2->p_vmspace->vm_ssize;
619 * Both processes are set up, now check if any loadable modules want
620 * to adjust anything.
621 * What if they have an error? XXX
623 TAILQ_FOREACH(ep, &fork_list, next) {
624 (*ep->function)(p1, p2, flags);
628 * Set the start time. Note that the process is not runnable. The
629 * caller is responsible for making it runnable.
631 microtime(&p2->p_start);
632 p2->p_acflag = AFORK;
635 * tell any interested parties about the new process
637 KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid);
640 * Return child proc pointer to parent.
646 lwkt_reltoken(&p2->p_token);
647 lwkt_reltoken(&p1->p_token);
649 lockmgr(&plkgrp->pg_lock, LK_RELEASE);
656 lwp_fork(struct lwp *origlp, struct proc *destproc, int flags)
658 globaldata_t gd = mycpu;
662 lp = kmalloc(sizeof(struct lwp), M_LWP, M_WAITOK|M_ZERO);
664 lp->lwp_proc = destproc;
665 lp->lwp_vmspace = destproc->p_vmspace;
666 lp->lwp_stat = LSRUN;
667 bcopy(&origlp->lwp_startcopy, &lp->lwp_startcopy,
668 (unsigned) ((caddr_t)&lp->lwp_endcopy -
669 (caddr_t)&lp->lwp_startcopy));
670 lp->lwp_flags |= origlp->lwp_flags & LWP_ALTSTACK;
672 * Set cpbase to the last timeout that occured (not the upcoming
675 * A critical section is required since a timer IPI can update
676 * scheduler specific data.
679 lp->lwp_cpbase = gd->gd_schedclock.time - gd->gd_schedclock.periodic;
680 destproc->p_usched->heuristic_forking(origlp, lp);
682 CPUMASK_ANDMASK(lp->lwp_cpumask, usched_mastermask);
683 lwkt_token_init(&lp->lwp_token, "lwp_token");
684 spin_init(&lp->lwp_spin, "lwptoken");
687 * Assign the thread to the current cpu to begin with so we
690 td = lwkt_alloc_thread(NULL, LWKT_THREAD_STACK, gd->gd_cpuid, 0);
692 td->td_ucred = crhold(destproc->p_ucred);
693 td->td_proc = destproc;
695 td->td_switch = cpu_heavy_switch;
696 #ifdef NO_LWKT_SPLIT_USERPRI
697 lwkt_setpri(td, TDPRI_USER_NORM);
699 lwkt_setpri(td, TDPRI_KERN_USER);
701 lwkt_set_comm(td, "%s", destproc->p_comm);
704 * cpu_fork will copy and update the pcb, set up the kernel stack,
705 * and make the child ready to run.
707 cpu_fork(origlp, lp, flags);
708 kqueue_init(&lp->lwp_kqueue, destproc->p_fd);
711 * Assign a TID to the lp. Loop until the insert succeeds (returns
714 lp->lwp_tid = destproc->p_lasttid;
716 if (++lp->lwp_tid < 0)
718 } while (lwp_rb_tree_RB_INSERT(&destproc->p_lwp_tree, lp) != NULL);
719 destproc->p_lasttid = lp->lwp_tid;
720 destproc->p_nthreads++;
723 * This flag is set and never cleared. It means that the process
724 * was threaded at some point. Used to improve exit performance.
726 destproc->p_flags |= P_MAYBETHREADED;
732 * The next two functionms are general routines to handle adding/deleting
733 * items on the fork callout list.
736 * Take the arguments given and put them onto the fork callout list,
737 * However first make sure that it's not already there.
738 * Returns 0 on success or a standard error number.
741 at_fork(forklist_fn function)
746 /* let the programmer know if he's been stupid */
747 if (rm_at_fork(function)) {
748 kprintf("WARNING: fork callout entry (%p) already present\n",
752 ep = kmalloc(sizeof(*ep), M_ATFORK, M_WAITOK|M_ZERO);
753 ep->function = function;
754 TAILQ_INSERT_TAIL(&fork_list, ep, next);
759 * Scan the exit callout list for the given item and remove it..
760 * Returns the number of items removed (0 or 1)
763 rm_at_fork(forklist_fn function)
767 TAILQ_FOREACH(ep, &fork_list, next) {
768 if (ep->function == function) {
769 TAILQ_REMOVE(&fork_list, ep, next);
778 * Add a forked process to the run queue after any remaining setup, such
779 * as setting the fork handler, has been completed.
781 * p2 is held by the caller.
784 start_forked_proc(struct lwp *lp1, struct proc *p2)
786 struct lwp *lp2 = ONLY_LWP_IN_PROC(p2);
790 * Move from SIDL to RUN queue, and activate the process's thread.
791 * Activation of the thread effectively makes the process "a"
792 * current process, so we do not setrunqueue().
794 * YYY setrunqueue works here but we should clean up the trampoline
795 * code so we just schedule the LWKT thread and let the trampoline
796 * deal with the userland scheduler on return to userland.
798 KASSERT(p2->p_stat == SIDL,
799 ("cannot start forked process, bad status: %p", p2));
800 p2->p_usched->resetpriority(lp2);
802 p2->p_stat = SACTIVE;
803 lp2->lwp_stat = LSRUN;
804 p2->p_usched->setrunqueue(lp2);
808 * Now can be swapped.
810 PRELE(lp1->lwp_proc);
813 * Preserve synchronization semantics of vfork. P_PPWAIT is set in
814 * the child until it has retired the parent's resources. The parent
815 * must wait for the flag to be cleared by the child.
817 * Interlock the flag/tsleep with atomic ops to avoid unnecessary
820 * XXX Is this use of an atomic op on a field that is not normally
821 * manipulated with atomic ops ok?
823 while ((pflags = p2->p_flags) & P_PPWAIT) {
825 tsleep_interlock(lp1->lwp_proc, 0);
826 if (atomic_cmpset_int(&p2->p_flags, pflags, pflags))
827 tsleep(lp1->lwp_proc, PINTERLOCKED, "ppwait", 0);
832 * procctl (idtype_t idtype, id_t id, int cmd, void *arg)
835 sys_procctl(struct procctl_args *uap)
837 struct proc *p = curproc;
839 struct sysreaper *reap;
840 union reaper_info udata;
843 if (uap->idtype != P_PID || uap->id != (id_t)p->p_pid)
847 case PROC_REAP_ACQUIRE:
848 lwkt_gettoken(&p->p_token);
849 reap = kmalloc(sizeof(*reap), M_REAPER, M_WAITOK|M_ZERO);
850 if (p->p_reaper == NULL || p->p_reaper->p != p) {
851 reaper_init(p, reap);
854 kfree(reap, M_REAPER);
857 lwkt_reltoken(&p->p_token);
859 case PROC_REAP_RELEASE:
860 lwkt_gettoken(&p->p_token);
863 KKASSERT(reap != NULL);
865 reaper_hold(reap); /* in case of thread race */
866 lockmgr(&reap->lock, LK_EXCLUSIVE);
868 lockmgr(&reap->lock, LK_RELEASE);
873 p->p_reaper = reap->parent;
875 reaper_hold(p->p_reaper);
876 lockmgr(&reap->lock, LK_RELEASE);
877 reaper_drop(reap); /* our ref */
878 reaper_drop(reap); /* old p_reaper ref */
883 lwkt_reltoken(&p->p_token);
885 case PROC_REAP_STATUS:
886 bzero(&udata, sizeof(udata));
887 lwkt_gettoken_shared(&p->p_token);
888 if ((reap = p->p_reaper) != NULL && reap->p == p) {
889 udata.status.flags = reap->flags;
890 udata.status.refs = reap->refs - 1; /* minus ours */
892 p2 = LIST_FIRST(&p->p_children);
893 udata.status.pid_head = p2 ? p2->p_pid : -1;
894 lwkt_reltoken(&p->p_token);
897 error = copyout(&udata, uap->data,
898 sizeof(udata.status));
911 * Bump ref on reaper, preventing destruction
914 reaper_hold(struct sysreaper *reap)
916 KKASSERT(reap->refs > 0);
917 refcount_acquire(&reap->refs);
921 * Drop ref on reaper, destroy the structure on the 1->0
922 * transition and loop on the parent.
925 reaper_drop(struct sysreaper *next)
927 struct sysreaper *reap;
929 while ((reap = next) != NULL) {
930 if (refcount_release(&reap->refs)) {
932 KKASSERT(reap->p == NULL);
934 kfree(reap, M_REAPER);
942 * Initialize a static or newly allocated reaper structure
945 reaper_init(struct proc *p, struct sysreaper *reap)
947 reap->parent = p->p_reaper;
950 reap->flags = REAPER_STAT_OWNED | REAPER_STAT_REALINIT;
953 reap->flags = REAPER_STAT_OWNED;
956 lockinit(&reap->lock, "subrp", 0, 0);
962 * Called with p->p_token held during exit.
964 * This is a bit simpler than RELEASE because there are no threads remaining
965 * to race. We only release if we own the reaper, the exit code will handle
966 * the final p_reaper release.
969 reaper_exit(struct proc *p)
971 struct sysreaper *reap;
974 * Release acquired reaper
976 if ((reap = p->p_reaper) != NULL && reap->p == p) {
977 lockmgr(&reap->lock, LK_EXCLUSIVE);
978 p->p_reaper = reap->parent;
980 reaper_hold(p->p_reaper);
982 lockmgr(&reap->lock, LK_RELEASE);
987 * Return and clear reaper (caller is holding p_token for us)
988 * (reap->p does not equal p). Caller must drop it.
990 if ((reap = p->p_reaper) != NULL) {
997 * Return a held (PHOLD) process representing the reaper for process (p).
998 * NULL should not normally be returned. Caller should PRELE() the returned
999 * reaper process when finished.
1001 * Remove dead internal nodes while we are at it.
1003 * Process (p)'s token must be held on call.
1004 * The returned process's token is NOT acquired by this routine.
1007 reaper_get(struct sysreaper *reap)
1009 struct sysreaper *next;
1010 struct proc *reproc;
1016 * Extra hold for loop
1021 lockmgr(&reap->lock, LK_SHARED);
1029 lockmgr(&reap->lock, LK_RELEASE);
1037 lockmgr(&reap->lock, LK_RELEASE);
1042 * Traverse upwards in the reaper topology, destroy
1043 * dead internal nodes when possible.
1045 * NOTE: Our ref on next means that a dead node should
1046 * have 2 (ours and reap->parent's).
1048 next = reap->parent;
1051 if (next->refs == 2 && next->p == NULL) {
1052 lockmgr(&reap->lock, LK_RELEASE);
1053 lockmgr(&reap->lock, LK_EXCLUSIVE);
1054 if (next->refs == 2 &&
1055 reap->parent == next &&
1058 * reap->parent inherits ref from next.
1060 reap->parent = next->parent;
1061 next->parent = NULL;
1062 reaper_drop(next); /* ours */
1063 reaper_drop(next); /* old parent */
1064 next = reap->parent;
1065 continue; /* possible chain */
1070 lockmgr(&reap->lock, LK_RELEASE);