The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_fork.c

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    1 /*-
    2  * Copyright (c) 1982, 1986, 1989, 1991, 1993
    3  *      The Regents of the University of California.  All rights reserved.
    4  * (c) UNIX System Laboratories, Inc.
    5  * All or some portions of this file are derived from material licensed
    6  * to the University of California by American Telephone and Telegraph
    7  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
    8  * the permission of UNIX System Laboratories, Inc.
    9  *
   10  * Redistribution and use in source and binary forms, with or without
   11  * modification, are permitted provided that the following conditions
   12  * are met:
   13  * 1. Redistributions of source code must retain the above copyright
   14  *    notice, this list of conditions and the following disclaimer.
   15  * 2. Redistributions in binary form must reproduce the above copyright
   16  *    notice, this list of conditions and the following disclaimer in the
   17  *    documentation and/or other materials provided with the distribution.
   18  * 4. Neither the name of the University nor the names of its contributors
   19  *    may be used to endorse or promote products derived from this software
   20  *    without specific prior written permission.
   21  *
   22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   32  * SUCH DAMAGE.
   33  *
   34  *      @(#)kern_fork.c 8.6 (Berkeley) 4/8/94
   35  */
   36 
   37 #include <sys/cdefs.h>
   38 __FBSDID("$FreeBSD$");
   39 
   40 #include "opt_kdtrace.h"
   41 #include "opt_ktrace.h"
   42 #include "opt_mac.h"
   43 
   44 #include <sys/param.h>
   45 #include <sys/systm.h>
   46 #include <sys/sysproto.h>
   47 #include <sys/eventhandler.h>
   48 #include <sys/filedesc.h>
   49 #include <sys/kernel.h>
   50 #include <sys/kthread.h>
   51 #include <sys/sysctl.h>
   52 #include <sys/lock.h>
   53 #include <sys/malloc.h>
   54 #include <sys/mutex.h>
   55 #include <sys/priv.h>
   56 #include <sys/proc.h>
   57 #include <sys/pioctl.h>
   58 #include <sys/resourcevar.h>
   59 #include <sys/sched.h>
   60 #include <sys/syscall.h>
   61 #include <sys/vmmeter.h>
   62 #include <sys/vnode.h>
   63 #include <sys/acct.h>
   64 #include <sys/ktr.h>
   65 #include <sys/ktrace.h>
   66 #include <sys/unistd.h> 
   67 #include <sys/sdt.h>
   68 #include <sys/sx.h>
   69 #include <sys/signalvar.h>
   70 
   71 #include <security/audit/audit.h>
   72 #include <security/mac/mac_framework.h>
   73 
   74 #include <vm/vm.h>
   75 #include <vm/pmap.h>
   76 #include <vm/vm_map.h>
   77 #include <vm/vm_extern.h>
   78 #include <vm/uma.h>
   79 
   80 #ifdef KDTRACE_HOOKS
   81 #include <sys/dtrace_bsd.h>
   82 dtrace_fork_func_t      dtrace_fasttrap_fork;
   83 #endif
   84 
   85 SDT_PROVIDER_DECLARE(proc);
   86 SDT_PROBE_DEFINE(proc, kernel, , create);
   87 SDT_PROBE_ARGTYPE(proc, kernel, , create, 0, "struct proc *");
   88 SDT_PROBE_ARGTYPE(proc, kernel, , create, 1, "struct proc *");
   89 SDT_PROBE_ARGTYPE(proc, kernel, , create, 2, "int");
   90 
   91 #ifndef _SYS_SYSPROTO_H_
   92 struct fork_args {
   93         int     dummy;
   94 };
   95 #endif
   96 
   97 /* ARGSUSED */
   98 int
   99 fork(td, uap)
  100         struct thread *td;
  101         struct fork_args *uap;
  102 {
  103         int error;
  104         struct proc *p2;
  105 
  106         error = fork1(td, RFFDG | RFPROC, 0, &p2);
  107         if (error == 0) {
  108                 td->td_retval[0] = p2->p_pid;
  109                 td->td_retval[1] = 0;
  110         }
  111         return (error);
  112 }
  113 
  114 /* ARGSUSED */
  115 int
  116 vfork(td, uap)
  117         struct thread *td;
  118         struct vfork_args *uap;
  119 {
  120         int error;
  121         struct proc *p2;
  122 
  123         error = fork1(td, RFFDG | RFPROC | RFPPWAIT | RFMEM, 0, &p2);
  124         if (error == 0) {
  125                 td->td_retval[0] = p2->p_pid;
  126                 td->td_retval[1] = 0;
  127         }
  128         return (error);
  129 }
  130 
  131 int
  132 rfork(td, uap)
  133         struct thread *td;
  134         struct rfork_args *uap;
  135 {
  136         struct proc *p2;
  137         int error;
  138 
  139         /* Don't allow kernel-only flags. */
  140         if ((uap->flags & RFKERNELONLY) != 0)
  141                 return (EINVAL);
  142 
  143         AUDIT_ARG(fflags, uap->flags);
  144         error = fork1(td, uap->flags, 0, &p2);
  145         if (error == 0) {
  146                 td->td_retval[0] = p2 ? p2->p_pid : 0;
  147                 td->td_retval[1] = 0;
  148         }
  149         return (error);
  150 }
  151 
  152 int     nprocs = 1;             /* process 0 */
  153 int     lastpid = 0;
  154 SYSCTL_INT(_kern, OID_AUTO, lastpid, CTLFLAG_RD, &lastpid, 0, 
  155     "Last used PID");
  156 
  157 /*
  158  * Random component to lastpid generation.  We mix in a random factor to make
  159  * it a little harder to predict.  We sanity check the modulus value to avoid
  160  * doing it in critical paths.  Don't let it be too small or we pointlessly
  161  * waste randomness entropy, and don't let it be impossibly large.  Using a
  162  * modulus that is too big causes a LOT more process table scans and slows
  163  * down fork processing as the pidchecked caching is defeated.
  164  */
  165 static int randompid = 0;
  166 
  167 static int
  168 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
  169 {
  170         int error, pid;
  171 
  172         error = sysctl_wire_old_buffer(req, sizeof(int));
  173         if (error != 0)
  174                 return(error);
  175         sx_xlock(&allproc_lock);
  176         pid = randompid;
  177         error = sysctl_handle_int(oidp, &pid, 0, req);
  178         if (error == 0 && req->newptr != NULL) {
  179                 if (pid < 0 || pid > PID_MAX - 100)     /* out of range */
  180                         pid = PID_MAX - 100;
  181                 else if (pid < 2)                       /* NOP */
  182                         pid = 0;
  183                 else if (pid < 100)                     /* Make it reasonable */
  184                         pid = 100;
  185                 randompid = pid;
  186         }
  187         sx_xunlock(&allproc_lock);
  188         return (error);
  189 }
  190 
  191 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
  192     0, 0, sysctl_kern_randompid, "I", "Random PID modulus");
  193 
  194 int
  195 fork1(td, flags, pages, procp)
  196         struct thread *td;
  197         int flags;
  198         int pages;
  199         struct proc **procp;
  200 {
  201         struct proc *p1, *p2, *pptr;
  202         struct proc *newproc;
  203         int ok, trypid;
  204         static int curfail, pidchecked = 0;
  205         static struct timeval lastfail;
  206         struct filedesc *fd;
  207         struct filedesc_to_leader *fdtol;
  208         struct thread *td2;
  209         struct sigacts *newsigacts;
  210         struct vmspace *vm2;
  211         int error;
  212 
  213         /* Can't copy and clear. */
  214         if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
  215                 return (EINVAL);
  216 
  217         p1 = td->td_proc;
  218 
  219         /*
  220          * Here we don't create a new process, but we divorce
  221          * certain parts of a process from itself.
  222          */
  223         if ((flags & RFPROC) == 0) {
  224                 if ((p1->p_flag & P_HADTHREADS) &&
  225                     (flags & (RFCFDG | RFFDG))) {
  226                         PROC_LOCK(p1);
  227                         if (thread_single(SINGLE_BOUNDARY)) {
  228                                 PROC_UNLOCK(p1);
  229                                 return (ERESTART);
  230                         }
  231                         PROC_UNLOCK(p1);
  232                 }
  233 
  234                 error = vm_forkproc(td, NULL, NULL, NULL, flags);
  235                 if (error)
  236                         goto norfproc_fail;
  237 
  238                 /*
  239                  * Close all file descriptors.
  240                  */
  241                 if (flags & RFCFDG) {
  242                         struct filedesc *fdtmp;
  243                         fdtmp = fdinit(td->td_proc->p_fd);
  244                         fdfree(td);
  245                         p1->p_fd = fdtmp;
  246                 }
  247 
  248                 /*
  249                  * Unshare file descriptors (from parent).
  250                  */
  251                 if (flags & RFFDG) 
  252                         fdunshare(p1, td);
  253 
  254 norfproc_fail:
  255                 if ((p1->p_flag & P_HADTHREADS) &&
  256                     (flags & (RFCFDG | RFFDG))) {
  257                         PROC_LOCK(p1);
  258                         thread_single_end();
  259                         PROC_UNLOCK(p1);
  260                 }
  261                 *procp = NULL;
  262                 return (error);
  263         }
  264 
  265         vm2 = NULL;
  266         /* Allocate new proc. */
  267         newproc = uma_zalloc(proc_zone, M_WAITOK);
  268         if (TAILQ_EMPTY(&newproc->p_threads)) {
  269                 td2 = thread_alloc();
  270                 if (td2 == NULL) {
  271                         error = ENOMEM;
  272                         goto fail1;
  273                 }
  274                 proc_linkup(newproc, td2);
  275                 sched_newproc(newproc, td2);
  276         } else
  277                 td2 = FIRST_THREAD_IN_PROC(newproc);
  278 
  279         /* Allocate and switch to an alternate kstack if specified. */
  280         if (pages != 0) {
  281                 if (!vm_thread_new_altkstack(td2, pages)) {
  282                         error = ENOMEM;
  283                         goto fail1;
  284                 }
  285         }
  286         if ((flags & RFMEM) == 0) {
  287                 vm2 = vmspace_fork(p1->p_vmspace);
  288                 if (vm2 == NULL) {
  289                         error = ENOMEM;
  290                         goto fail1;
  291                 }
  292         }
  293 #ifdef MAC
  294         mac_init_proc(newproc);
  295 #endif
  296         knlist_init(&newproc->p_klist, &newproc->p_mtx, NULL, NULL, NULL);
  297         STAILQ_INIT(&newproc->p_ktr);
  298 
  299         /* We have to lock the process tree while we look for a pid. */
  300         sx_slock(&proctree_lock);
  301 
  302         /*
  303          * Although process entries are dynamically created, we still keep
  304          * a global limit on the maximum number we will create.  Don't allow
  305          * a nonprivileged user to use the last ten processes; don't let root
  306          * exceed the limit. The variable nprocs is the current number of
  307          * processes, maxproc is the limit.
  308          */
  309         sx_xlock(&allproc_lock);
  310         if ((nprocs >= maxproc - 10 && priv_check_cred(td->td_ucred,
  311             PRIV_MAXPROC, 0) != 0) || nprocs >= maxproc) {
  312                 error = EAGAIN;
  313                 goto fail;
  314         }
  315 
  316         /*
  317          * Increment the count of procs running with this uid. Don't allow
  318          * a nonprivileged user to exceed their current limit.
  319          *
  320          * XXXRW: Can we avoid privilege here if it's not needed?
  321          */
  322         error = priv_check_cred(td->td_ucred, PRIV_PROC_LIMIT, 0);
  323         if (error == 0)
  324                 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1, 0);
  325         else {
  326                 PROC_LOCK(p1);
  327                 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1,
  328                     lim_cur(p1, RLIMIT_NPROC));
  329                 PROC_UNLOCK(p1);
  330         }
  331         if (!ok) {
  332                 error = EAGAIN;
  333                 goto fail;
  334         }
  335 
  336         /*
  337          * Increment the nprocs resource before blocking can occur.  There
  338          * are hard-limits as to the number of processes that can run.
  339          */
  340         nprocs++;
  341 
  342         /*
  343          * Find an unused process ID.  We remember a range of unused IDs
  344          * ready to use (from lastpid+1 through pidchecked-1).
  345          *
  346          * If RFHIGHPID is set (used during system boot), do not allocate
  347          * low-numbered pids.
  348          */
  349         trypid = lastpid + 1;
  350         if (flags & RFHIGHPID) {
  351                 if (trypid < 10)
  352                         trypid = 10;
  353         } else {
  354                 if (randompid)
  355                         trypid += arc4random() % randompid;
  356         }
  357 retry:
  358         /*
  359          * If the process ID prototype has wrapped around,
  360          * restart somewhat above 0, as the low-numbered procs
  361          * tend to include daemons that don't exit.
  362          */
  363         if (trypid >= PID_MAX) {
  364                 trypid = trypid % PID_MAX;
  365                 if (trypid < 100)
  366                         trypid += 100;
  367                 pidchecked = 0;
  368         }
  369         if (trypid >= pidchecked) {
  370                 int doingzomb = 0;
  371 
  372                 pidchecked = PID_MAX;
  373                 /*
  374                  * Scan the active and zombie procs to check whether this pid
  375                  * is in use.  Remember the lowest pid that's greater
  376                  * than trypid, so we can avoid checking for a while.
  377                  */
  378                 p2 = LIST_FIRST(&allproc);
  379 again:
  380                 for (; p2 != NULL; p2 = LIST_NEXT(p2, p_list)) {
  381                         while (p2->p_pid == trypid ||
  382                             (p2->p_pgrp != NULL &&
  383                             (p2->p_pgrp->pg_id == trypid ||
  384                             (p2->p_session != NULL &&
  385                             p2->p_session->s_sid == trypid)))) {
  386                                 trypid++;
  387                                 if (trypid >= pidchecked)
  388                                         goto retry;
  389                         }
  390                         if (p2->p_pid > trypid && pidchecked > p2->p_pid)
  391                                 pidchecked = p2->p_pid;
  392                         if (p2->p_pgrp != NULL) {
  393                                 if (p2->p_pgrp->pg_id > trypid &&
  394                                     pidchecked > p2->p_pgrp->pg_id)
  395                                         pidchecked = p2->p_pgrp->pg_id;
  396                                 if (p2->p_session != NULL &&
  397                                     p2->p_session->s_sid > trypid &&
  398                                     pidchecked > p2->p_session->s_sid)
  399                                         pidchecked = p2->p_session->s_sid;
  400                         }
  401                 }
  402                 if (!doingzomb) {
  403                         doingzomb = 1;
  404                         p2 = LIST_FIRST(&zombproc);
  405                         goto again;
  406                 }
  407         }
  408         sx_sunlock(&proctree_lock);
  409 
  410         /*
  411          * RFHIGHPID does not mess with the lastpid counter during boot.
  412          */
  413         if (flags & RFHIGHPID)
  414                 pidchecked = 0;
  415         else
  416                 lastpid = trypid;
  417 
  418         p2 = newproc;
  419         p2->p_state = PRS_NEW;          /* protect against others */
  420         p2->p_pid = trypid;
  421         /*
  422          * Allow the scheduler to initialize the child.
  423          */
  424         thread_lock(td);
  425         sched_fork(td, td2);
  426         thread_unlock(td);
  427         AUDIT_ARG(pid, p2->p_pid);
  428         LIST_INSERT_HEAD(&allproc, p2, p_list);
  429         LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
  430 
  431         PROC_LOCK(p2);
  432         PROC_LOCK(p1);
  433 
  434         sx_xunlock(&allproc_lock);
  435 
  436         bcopy(&p1->p_startcopy, &p2->p_startcopy,
  437             __rangeof(struct proc, p_startcopy, p_endcopy));
  438         pargs_hold(p2->p_args);
  439         PROC_UNLOCK(p1);
  440 
  441         bzero(&p2->p_startzero,
  442             __rangeof(struct proc, p_startzero, p_endzero));
  443 
  444         p2->p_ucred = crhold(td->td_ucred);
  445         PROC_UNLOCK(p2);
  446 
  447         /*
  448          * Malloc things while we don't hold any locks.
  449          */
  450         if (flags & RFSIGSHARE)
  451                 newsigacts = NULL;
  452         else
  453                 newsigacts = sigacts_alloc();
  454 
  455         /*
  456          * Copy filedesc.
  457          */
  458         if (flags & RFCFDG) {
  459                 fd = fdinit(p1->p_fd);
  460                 fdtol = NULL;
  461         } else if (flags & RFFDG) {
  462                 fd = fdcopy(p1->p_fd);
  463                 fdtol = NULL;
  464         } else {
  465                 fd = fdshare(p1->p_fd);
  466                 if (p1->p_fdtol == NULL)
  467                         p1->p_fdtol =
  468                                 filedesc_to_leader_alloc(NULL,
  469                                                          NULL,
  470                                                          p1->p_leader);
  471                 if ((flags & RFTHREAD) != 0) {
  472                         /*
  473                          * Shared file descriptor table and
  474                          * shared process leaders.
  475                          */
  476                         fdtol = p1->p_fdtol;
  477                         FILEDESC_XLOCK(p1->p_fd);
  478                         fdtol->fdl_refcount++;
  479                         FILEDESC_XUNLOCK(p1->p_fd);
  480                 } else {
  481                         /* 
  482                          * Shared file descriptor table, and
  483                          * different process leaders 
  484                          */
  485                         fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
  486                                                          p1->p_fd,
  487                                                          p2);
  488                 }
  489         }
  490         /*
  491          * Make a proc table entry for the new process.
  492          * Start by zeroing the section of proc that is zero-initialized,
  493          * then copy the section that is copied directly from the parent.
  494          */
  495 
  496         PROC_LOCK(p2);
  497         PROC_LOCK(p1);
  498 
  499         bzero(&td2->td_startzero,
  500             __rangeof(struct thread, td_startzero, td_endzero));
  501 
  502         bcopy(&td->td_startcopy, &td2->td_startcopy,
  503             __rangeof(struct thread, td_startcopy, td_endcopy));
  504 
  505         td2->td_sigstk = td->td_sigstk;
  506         td2->td_sigmask = td->td_sigmask;
  507         td2->td_flags = TDF_INMEM;
  508 
  509         /*
  510          * Duplicate sub-structures as needed.
  511          * Increase reference counts on shared objects.
  512          */
  513         p2->p_flag = P_INMEM;
  514         p2->p_swtick = ticks;
  515         if (p1->p_flag & P_PROFIL)
  516                 startprofclock(p2);
  517         td2->td_ucred = crhold(p2->p_ucred);
  518 
  519         if (flags & RFSIGSHARE) {
  520                 p2->p_sigacts = sigacts_hold(p1->p_sigacts);
  521         } else {
  522                 sigacts_copy(newsigacts, p1->p_sigacts);
  523                 p2->p_sigacts = newsigacts;
  524         }
  525         if (flags & RFLINUXTHPN) 
  526                 p2->p_sigparent = SIGUSR1;
  527         else
  528                 p2->p_sigparent = SIGCHLD;
  529 
  530         p2->p_textvp = p1->p_textvp;
  531         p2->p_fd = fd;
  532         p2->p_fdtol = fdtol;
  533 
  534         /*
  535          * p_limit is copy-on-write.  Bump its refcount.
  536          */
  537         lim_fork(p1, p2);
  538 
  539         pstats_fork(p1->p_stats, p2->p_stats);
  540 
  541         PROC_UNLOCK(p1);
  542         PROC_UNLOCK(p2);
  543 
  544         /* Bump references to the text vnode (for procfs) */
  545         if (p2->p_textvp)
  546                 vref(p2->p_textvp);
  547 
  548         /*
  549          * Set up linkage for kernel based threading.
  550          */
  551         if ((flags & RFTHREAD) != 0) {
  552                 mtx_lock(&ppeers_lock);
  553                 p2->p_peers = p1->p_peers;
  554                 p1->p_peers = p2;
  555                 p2->p_leader = p1->p_leader;
  556                 mtx_unlock(&ppeers_lock);
  557                 PROC_LOCK(p1->p_leader);
  558                 if ((p1->p_leader->p_flag & P_WEXIT) != 0) {
  559                         PROC_UNLOCK(p1->p_leader);
  560                         /*
  561                          * The task leader is exiting, so process p1 is
  562                          * going to be killed shortly.  Since p1 obviously
  563                          * isn't dead yet, we know that the leader is either
  564                          * sending SIGKILL's to all the processes in this
  565                          * task or is sleeping waiting for all the peers to
  566                          * exit.  We let p1 complete the fork, but we need
  567                          * to go ahead and kill the new process p2 since
  568                          * the task leader may not get a chance to send
  569                          * SIGKILL to it.  We leave it on the list so that
  570                          * the task leader will wait for this new process
  571                          * to commit suicide.
  572                          */
  573                         PROC_LOCK(p2);
  574                         psignal(p2, SIGKILL);
  575                         PROC_UNLOCK(p2);
  576                 } else
  577                         PROC_UNLOCK(p1->p_leader);
  578         } else {
  579                 p2->p_peers = NULL;
  580                 p2->p_leader = p2;
  581         }
  582 
  583         sx_xlock(&proctree_lock);
  584         PGRP_LOCK(p1->p_pgrp);
  585         PROC_LOCK(p2);
  586         PROC_LOCK(p1);
  587 
  588         /*
  589          * Preserve some more flags in subprocess.  P_PROFIL has already
  590          * been preserved.
  591          */
  592         p2->p_flag |= p1->p_flag & P_SUGID;
  593         td2->td_pflags |= td->td_pflags & TDP_ALTSTACK;
  594         SESS_LOCK(p1->p_session);
  595         if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
  596                 p2->p_flag |= P_CONTROLT;
  597         SESS_UNLOCK(p1->p_session);
  598         if (flags & RFPPWAIT)
  599                 p2->p_flag |= P_PPWAIT;
  600 
  601         p2->p_pgrp = p1->p_pgrp;
  602         LIST_INSERT_AFTER(p1, p2, p_pglist);
  603         PGRP_UNLOCK(p1->p_pgrp);
  604         LIST_INIT(&p2->p_children);
  605 
  606         callout_init(&p2->p_itcallout, CALLOUT_MPSAFE);
  607 
  608 #ifdef KTRACE
  609         /*
  610          * Copy traceflag and tracefile if enabled.
  611          */
  612         mtx_lock(&ktrace_mtx);
  613         KASSERT(p2->p_tracevp == NULL, ("new process has a ktrace vnode"));
  614         if (p1->p_traceflag & KTRFAC_INHERIT) {
  615                 p2->p_traceflag = p1->p_traceflag;
  616                 if ((p2->p_tracevp = p1->p_tracevp) != NULL) {
  617                         VREF(p2->p_tracevp);
  618                         KASSERT(p1->p_tracecred != NULL,
  619                             ("ktrace vnode with no cred"));
  620                         p2->p_tracecred = crhold(p1->p_tracecred);
  621                 }
  622         }
  623         mtx_unlock(&ktrace_mtx);
  624 #endif
  625 
  626         /*
  627          * If PF_FORK is set, the child process inherits the
  628          * procfs ioctl flags from its parent.
  629          */
  630         if (p1->p_pfsflags & PF_FORK) {
  631                 p2->p_stops = p1->p_stops;
  632                 p2->p_pfsflags = p1->p_pfsflags;
  633         }
  634 
  635 #ifdef KDTRACE_HOOKS
  636         /*
  637          * Tell the DTrace fasttrap provider about the new process
  638          * if it has registered an interest.
  639          */
  640         if (dtrace_fasttrap_fork)
  641                 dtrace_fasttrap_fork(p1, p2);
  642 #endif
  643 
  644         /*
  645          * This begins the section where we must prevent the parent
  646          * from being swapped.
  647          */
  648         _PHOLD(p1);
  649         PROC_UNLOCK(p1);
  650 
  651         /*
  652          * Attach the new process to its parent.
  653          *
  654          * If RFNOWAIT is set, the newly created process becomes a child
  655          * of init.  This effectively disassociates the child from the
  656          * parent.
  657          */
  658         if (flags & RFNOWAIT)
  659                 pptr = initproc;
  660         else
  661                 pptr = p1;
  662         p2->p_pptr = pptr;
  663         LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
  664         sx_xunlock(&proctree_lock);
  665 
  666         /* Inform accounting that we have forked. */
  667         p2->p_acflag = AFORK;
  668         PROC_UNLOCK(p2);
  669 
  670         /*
  671          * Finish creating the child process.  It will return via a different
  672          * execution path later.  (ie: directly into user mode)
  673          */
  674         vm_forkproc(td, p2, td2, vm2, flags);
  675 
  676         if (flags == (RFFDG | RFPROC)) {
  677                 PCPU_INC(cnt.v_forks);
  678                 PCPU_ADD(cnt.v_forkpages, p2->p_vmspace->vm_dsize +
  679                     p2->p_vmspace->vm_ssize);
  680         } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
  681                 PCPU_INC(cnt.v_vforks);
  682                 PCPU_ADD(cnt.v_vforkpages, p2->p_vmspace->vm_dsize +
  683                     p2->p_vmspace->vm_ssize);
  684         } else if (p1 == &proc0) {
  685                 PCPU_INC(cnt.v_kthreads);
  686                 PCPU_ADD(cnt.v_kthreadpages, p2->p_vmspace->vm_dsize +
  687                     p2->p_vmspace->vm_ssize);
  688         } else {
  689                 PCPU_INC(cnt.v_rforks);
  690                 PCPU_ADD(cnt.v_rforkpages, p2->p_vmspace->vm_dsize +
  691                     p2->p_vmspace->vm_ssize);
  692         }
  693 
  694         /*
  695          * Both processes are set up, now check if any loadable modules want
  696          * to adjust anything.
  697          *   What if they have an error? XXX
  698          */
  699         EVENTHANDLER_INVOKE(process_fork, p1, p2, flags);
  700 
  701         /*
  702          * Set the child start time and mark the process as being complete.
  703          */
  704         microuptime(&p2->p_stats->p_start);
  705         PROC_SLOCK(p2);
  706         p2->p_state = PRS_NORMAL;
  707         PROC_SUNLOCK(p2);
  708 
  709         /*
  710          * If RFSTOPPED not requested, make child runnable and add to
  711          * run queue.
  712          */
  713         if ((flags & RFSTOPPED) == 0) {
  714                 thread_lock(td2);
  715                 TD_SET_CAN_RUN(td2);
  716                 sched_add(td2, SRQ_BORING);
  717                 thread_unlock(td2);
  718         }
  719 
  720         /*
  721          * Now can be swapped.
  722          */
  723         PROC_LOCK(p1);
  724         _PRELE(p1);
  725         PROC_UNLOCK(p1);
  726 
  727         /*
  728          * Tell any interested parties about the new process.
  729          */
  730         knote_fork(&p1->p_klist, p2->p_pid);
  731         SDT_PROBE(proc, kernel, , create, p2, p1, flags, 0, 0);
  732 
  733         /*
  734          * Preserve synchronization semantics of vfork.  If waiting for
  735          * child to exec or exit, set P_PPWAIT on child, and sleep on our
  736          * proc (in case of exit).
  737          */
  738         PROC_LOCK(p2);
  739         while (p2->p_flag & P_PPWAIT)
  740                 msleep(p1, &p2->p_mtx, PWAIT, "ppwait", 0);
  741         PROC_UNLOCK(p2);
  742 
  743         /*
  744          * Return child proc pointer to parent.
  745          */
  746         *procp = p2;
  747         return (0);
  748 fail:
  749         sx_sunlock(&proctree_lock);
  750         if (ppsratecheck(&lastfail, &curfail, 1))
  751                 printf("maxproc limit exceeded by uid %i, please see tuning(7) and login.conf(5).\n",
  752                     td->td_ucred->cr_ruid);
  753         sx_xunlock(&allproc_lock);
  754 #ifdef MAC
  755         mac_destroy_proc(newproc);
  756 #endif
  757 fail1:
  758         if (vm2 != NULL)
  759                 vmspace_free(vm2);
  760         uma_zfree(proc_zone, newproc);
  761         pause("fork", hz / 2);
  762         return (error);
  763 }
  764 
  765 /*
  766  * Handle the return of a child process from fork1().  This function
  767  * is called from the MD fork_trampoline() entry point.
  768  */
  769 void
  770 fork_exit(callout, arg, frame)
  771         void (*callout)(void *, struct trapframe *);
  772         void *arg;
  773         struct trapframe *frame;
  774 {
  775         struct proc *p;
  776         struct thread *td;
  777         struct thread *dtd;
  778 
  779         td = curthread;
  780         p = td->td_proc;
  781         KASSERT(p->p_state == PRS_NORMAL, ("executing process is still new"));
  782 
  783         CTR4(KTR_PROC, "fork_exit: new thread %p (kse %p, pid %d, %s)",
  784                 td, td->td_sched, p->p_pid, p->p_comm);
  785 
  786         sched_fork_exit(td);
  787         /*
  788         * Processes normally resume in mi_switch() after being
  789         * cpu_switch()'ed to, but when children start up they arrive here
  790         * instead, so we must do much the same things as mi_switch() would.
  791         */
  792         if ((dtd = PCPU_GET(deadthread))) {
  793                 PCPU_SET(deadthread, NULL);
  794                 thread_stash(dtd);
  795         }
  796         thread_unlock(td);
  797 
  798         /*
  799          * cpu_set_fork_handler intercepts this function call to
  800          * have this call a non-return function to stay in kernel mode.
  801          * initproc has its own fork handler, but it does return.
  802          */
  803         KASSERT(callout != NULL, ("NULL callout in fork_exit"));
  804         callout(arg, frame);
  805 
  806         /*
  807          * Check if a kernel thread misbehaved and returned from its main
  808          * function.
  809          */
  810         if (p->p_flag & P_KTHREAD) {
  811                 printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
  812                     p->p_comm, p->p_pid);
  813                 kthread_exit(0);
  814         }
  815         mtx_assert(&Giant, MA_NOTOWNED);
  816 
  817         EVENTHANDLER_INVOKE(schedtail, p);
  818 }
  819 
  820 /*
  821  * Simplified back end of syscall(), used when returning from fork()
  822  * directly into user mode.  Giant is not held on entry, and must not
  823  * be held on return.  This function is passed in to fork_exit() as the
  824  * first parameter and is called when returning to a new userland process.
  825  */
  826 void
  827 fork_return(td, frame)
  828         struct thread *td;
  829         struct trapframe *frame;
  830 {
  831 
  832         userret(td, frame);
  833 #ifdef KTRACE
  834         if (KTRPOINT(td, KTR_SYSRET))
  835                 ktrsysret(SYS_fork, 0, 0);
  836 #endif
  837         mtx_assert(&Giant, MA_NOTOWNED);
  838 }

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