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_ktrace.h"
   41 #include "opt_mac.h"
   42 
   43 #include <sys/param.h>
   44 #include <sys/systm.h>
   45 #include <sys/sysproto.h>
   46 #include <sys/eventhandler.h>
   47 #include <sys/filedesc.h>
   48 #include <sys/kernel.h>
   49 #include <sys/kthread.h>
   50 #include <sys/sysctl.h>
   51 #include <sys/lock.h>
   52 #include <sys/malloc.h>
   53 #include <sys/mutex.h>
   54 #include <sys/proc.h>
   55 #include <sys/pioctl.h>
   56 #include <sys/resourcevar.h>
   57 #include <sys/sched.h>
   58 #include <sys/syscall.h>
   59 #include <sys/vmmeter.h>
   60 #include <sys/vnode.h>
   61 #include <sys/acct.h>
   62 #include <sys/mac.h>
   63 #include <sys/ktr.h>
   64 #include <sys/ktrace.h>
   65 #include <sys/unistd.h> 
   66 #include <sys/sx.h>
   67 #include <sys/signalvar.h>
   68 
   69 #include <security/audit/audit.h>
   70 
   71 #include <vm/vm.h>
   72 #include <vm/pmap.h>
   73 #include <vm/vm_map.h>
   74 #include <vm/vm_extern.h>
   75 #include <vm/uma.h>
   76 
   77 
   78 #ifndef _SYS_SYSPROTO_H_
   79 struct fork_args {
   80         int     dummy;
   81 };
   82 #endif
   83 
   84 static int forksleep; /* Place for fork1() to sleep on. */
   85 
   86 /*
   87  * MPSAFE
   88  */
   89 /* ARGSUSED */
   90 int
   91 fork(td, uap)
   92         struct thread *td;
   93         struct fork_args *uap;
   94 {
   95         int error;
   96         struct proc *p2;
   97 
   98         error = fork1(td, RFFDG | RFPROC, 0, &p2);
   99         if (error == 0) {
  100                 td->td_retval[0] = p2->p_pid;
  101                 td->td_retval[1] = 0;
  102         }
  103         return (error);
  104 }
  105 
  106 /*
  107  * MPSAFE
  108  */
  109 /* ARGSUSED */
  110 int
  111 vfork(td, uap)
  112         struct thread *td;
  113         struct vfork_args *uap;
  114 {
  115         int error;
  116         struct proc *p2;
  117 
  118         error = fork1(td, RFFDG | RFPROC | RFPPWAIT | RFMEM, 0, &p2);
  119         if (error == 0) {
  120                 td->td_retval[0] = p2->p_pid;
  121                 td->td_retval[1] = 0;
  122         }
  123         return (error);
  124 }
  125 
  126 /*
  127  * MPSAFE
  128  */
  129 int
  130 rfork(td, uap)
  131         struct thread *td;
  132         struct rfork_args *uap;
  133 {
  134         struct proc *p2;
  135         int error;
  136 
  137         /* Don't allow kernel-only flags. */
  138         if ((uap->flags & RFKERNELONLY) != 0)
  139                 return (EINVAL);
  140 
  141         AUDIT_ARG(fflags, uap->flags);
  142         error = fork1(td, uap->flags, 0, &p2);
  143         if (error == 0) {
  144                 td->td_retval[0] = p2 ? p2->p_pid : 0;
  145                 td->td_retval[1] = 0;
  146         }
  147         return (error);
  148 }
  149 
  150 int     nprocs = 1;             /* process 0 */
  151 int     lastpid = 0;
  152 SYSCTL_INT(_kern, OID_AUTO, lastpid, CTLFLAG_RD, &lastpid, 0, 
  153     "Last used PID");
  154 
  155 /*
  156  * Random component to lastpid generation.  We mix in a random factor to make
  157  * it a little harder to predict.  We sanity check the modulus value to avoid
  158  * doing it in critical paths.  Don't let it be too small or we pointlessly
  159  * waste randomness entropy, and don't let it be impossibly large.  Using a
  160  * modulus that is too big causes a LOT more process table scans and slows
  161  * down fork processing as the pidchecked caching is defeated.
  162  */
  163 static int randompid = 0;
  164 
  165 static int
  166 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
  167 {
  168         int error, pid;
  169 
  170         error = sysctl_wire_old_buffer(req, sizeof(int));
  171         if (error != 0)
  172                 return(error);
  173         sx_xlock(&allproc_lock);
  174         pid = randompid;
  175         error = sysctl_handle_int(oidp, &pid, 0, req);
  176         if (error == 0 && req->newptr != NULL) {
  177                 if (pid < 0 || pid > PID_MAX - 100)     /* out of range */
  178                         pid = PID_MAX - 100;
  179                 else if (pid < 2)                       /* NOP */
  180                         pid = 0;
  181                 else if (pid < 100)                     /* Make it reasonable */
  182                         pid = 100;
  183                 randompid = pid;
  184         }
  185         sx_xunlock(&allproc_lock);
  186         return (error);
  187 }
  188 
  189 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
  190     0, 0, sysctl_kern_randompid, "I", "Random PID modulus");
  191 
  192 int
  193 fork1(td, flags, pages, procp)
  194         struct thread *td;
  195         int flags;
  196         int pages;
  197         struct proc **procp;
  198 {
  199         struct proc *p1, *p2, *pptr;
  200         struct proc *newproc;
  201         int ok, trypid;
  202         static int curfail, pidchecked = 0;
  203         static struct timeval lastfail;
  204         struct filedesc *fd;
  205         struct filedesc_to_leader *fdtol;
  206         struct thread *td2;
  207         struct ksegrp *kg2;
  208         struct sigacts *newsigacts;
  209         int error;
  210 
  211         /* Can't copy and clear. */
  212         if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
  213                 return (EINVAL);
  214 
  215         p1 = td->td_proc;
  216 
  217         /*
  218          * Here we don't create a new process, but we divorce
  219          * certain parts of a process from itself.
  220          */
  221         if ((flags & RFPROC) == 0) {
  222                 if ((p1->p_flag & P_HADTHREADS) &&
  223                     (flags & (RFCFDG | RFFDG))) {
  224                         PROC_LOCK(p1);
  225                         if (thread_single(SINGLE_BOUNDARY)) {
  226                                 PROC_UNLOCK(p1);
  227                                 return (ERESTART);
  228                         }
  229                         PROC_UNLOCK(p1);
  230                 }
  231 
  232                 vm_forkproc(td, NULL, NULL, flags);
  233                 /*
  234                  * Close all file descriptors.
  235                  */
  236                 if (flags & RFCFDG) {
  237                         struct filedesc *fdtmp;
  238                         fdtmp = fdinit(td->td_proc->p_fd);
  239                         fdfree(td);
  240                         p1->p_fd = fdtmp;
  241                 }
  242 
  243                 /*
  244                  * Unshare file descriptors (from parent).
  245                  */
  246                 if (flags & RFFDG) 
  247                         fdunshare(p1, td);
  248 
  249                 if ((p1->p_flag & P_HADTHREADS) &&
  250                     (flags & (RFCFDG | RFFDG))) {
  251                         PROC_LOCK(p1);
  252                         thread_single_end();
  253                         PROC_UNLOCK(p1);
  254                 }
  255                 *procp = NULL;
  256                 return (0);
  257         }
  258 
  259         /* Allocate new proc. */
  260         newproc = uma_zalloc(proc_zone, M_WAITOK);
  261 #ifdef MAC
  262         mac_init_proc(newproc);
  263 #endif
  264 #ifdef AUDIT
  265         audit_proc_alloc(newproc);
  266 #endif
  267         knlist_init(&newproc->p_klist, &newproc->p_mtx, NULL, NULL, NULL);
  268         STAILQ_INIT(&newproc->p_ktr);
  269 
  270         /* We have to lock the process tree while we look for a pid. */
  271         sx_slock(&proctree_lock);
  272 
  273         /*
  274          * Although process entries are dynamically created, we still keep
  275          * a global limit on the maximum number we will create.  Don't allow
  276          * a nonprivileged user to use the last ten processes; don't let root
  277          * exceed the limit. The variable nprocs is the current number of
  278          * processes, maxproc is the limit.
  279          */
  280         sx_xlock(&allproc_lock);
  281         if ((nprocs >= maxproc - 10 &&
  282             suser_cred(td->td_ucred, SUSER_RUID) != 0) ||
  283             nprocs >= maxproc) {
  284                 error = EAGAIN;
  285                 goto fail;
  286         }
  287 
  288         /*
  289          * Increment the count of procs running with this uid. Don't allow
  290          * a nonprivileged user to exceed their current limit.
  291          */
  292         error = suser_cred(td->td_ucred, SUSER_RUID | SUSER_ALLOWJAIL);
  293         if (error == 0)
  294                 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1, 0);
  295         else {
  296                 PROC_LOCK(p1);
  297                 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1,
  298                     lim_cur(p1, RLIMIT_NPROC));
  299                 PROC_UNLOCK(p1);
  300         }
  301         if (!ok) {
  302                 error = EAGAIN;
  303                 goto fail;
  304         }
  305 
  306         /*
  307          * Increment the nprocs resource before blocking can occur.  There
  308          * are hard-limits as to the number of processes that can run.
  309          */
  310         nprocs++;
  311 
  312         /*
  313          * Find an unused process ID.  We remember a range of unused IDs
  314          * ready to use (from lastpid+1 through pidchecked-1).
  315          *
  316          * If RFHIGHPID is set (used during system boot), do not allocate
  317          * low-numbered pids.
  318          */
  319         trypid = lastpid + 1;
  320         if (flags & RFHIGHPID) {
  321                 if (trypid < 10)
  322                         trypid = 10;
  323         } else {
  324                 if (randompid)
  325                         trypid += arc4random() % randompid;
  326         }
  327 retry:
  328         /*
  329          * If the process ID prototype has wrapped around,
  330          * restart somewhat above 0, as the low-numbered procs
  331          * tend to include daemons that don't exit.
  332          */
  333         if (trypid >= PID_MAX) {
  334                 trypid = trypid % PID_MAX;
  335                 if (trypid < 100)
  336                         trypid += 100;
  337                 pidchecked = 0;
  338         }
  339         if (trypid >= pidchecked) {
  340                 int doingzomb = 0;
  341 
  342                 pidchecked = PID_MAX;
  343                 /*
  344                  * Scan the active and zombie procs to check whether this pid
  345                  * is in use.  Remember the lowest pid that's greater
  346                  * than trypid, so we can avoid checking for a while.
  347                  */
  348                 p2 = LIST_FIRST(&allproc);
  349 again:
  350                 for (; p2 != NULL; p2 = LIST_NEXT(p2, p_list)) {
  351                         PROC_LOCK(p2);
  352                         while (p2->p_pid == trypid ||
  353                             (p2->p_pgrp != NULL &&
  354                             (p2->p_pgrp->pg_id == trypid ||
  355                             (p2->p_session != NULL &&
  356                             p2->p_session->s_sid == trypid)))) {
  357                                 trypid++;
  358                                 if (trypid >= pidchecked) {
  359                                         PROC_UNLOCK(p2);
  360                                         goto retry;
  361                                 }
  362                         }
  363                         if (p2->p_pid > trypid && pidchecked > p2->p_pid)
  364                                 pidchecked = p2->p_pid;
  365                         if (p2->p_pgrp != NULL) {
  366                                 if (p2->p_pgrp->pg_id > trypid &&
  367                                     pidchecked > p2->p_pgrp->pg_id)
  368                                         pidchecked = p2->p_pgrp->pg_id;
  369                                 if (p2->p_session != NULL &&
  370                                     p2->p_session->s_sid > trypid &&
  371                                     pidchecked > p2->p_session->s_sid)
  372                                         pidchecked = p2->p_session->s_sid;
  373                         }
  374                         PROC_UNLOCK(p2);
  375                 }
  376                 if (!doingzomb) {
  377                         doingzomb = 1;
  378                         p2 = LIST_FIRST(&zombproc);
  379                         goto again;
  380                 }
  381         }
  382         sx_sunlock(&proctree_lock);
  383 
  384         /*
  385          * RFHIGHPID does not mess with the lastpid counter during boot.
  386          */
  387         if (flags & RFHIGHPID)
  388                 pidchecked = 0;
  389         else
  390                 lastpid = trypid;
  391 
  392         p2 = newproc;
  393         p2->p_state = PRS_NEW;          /* protect against others */
  394         p2->p_pid = trypid;
  395         AUDIT_ARG(pid, p2->p_pid);
  396         LIST_INSERT_HEAD(&allproc, p2, p_list);
  397         LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
  398 
  399         PROC_LOCK(p2);
  400         PROC_LOCK(p1);
  401 
  402         sx_xunlock(&allproc_lock);
  403 
  404         bcopy(&p1->p_startcopy, &p2->p_startcopy,
  405             __rangeof(struct proc, p_startcopy, p_endcopy));
  406         PROC_UNLOCK(p1);
  407 
  408         bzero(&p2->p_startzero,
  409             __rangeof(struct proc, p_startzero, p_endzero));
  410 
  411         p2->p_ucred = crhold(td->td_ucred);
  412         PROC_UNLOCK(p2);
  413 
  414         /*
  415          * Malloc things while we don't hold any locks.
  416          */
  417         if (flags & RFSIGSHARE)
  418                 newsigacts = NULL;
  419         else
  420                 newsigacts = sigacts_alloc();
  421 
  422         /*
  423          * Copy filedesc.
  424          */
  425         if (flags & RFCFDG) {
  426                 fd = fdinit(p1->p_fd);
  427                 fdtol = NULL;
  428         } else if (flags & RFFDG) {
  429                 fd = fdcopy(p1->p_fd);
  430                 fdtol = NULL;
  431         } else {
  432                 fd = fdshare(p1->p_fd);
  433                 if (p1->p_fdtol == NULL)
  434                         p1->p_fdtol =
  435                                 filedesc_to_leader_alloc(NULL,
  436                                                          NULL,
  437                                                          p1->p_leader);
  438                 if ((flags & RFTHREAD) != 0) {
  439                         /*
  440                          * Shared file descriptor table and
  441                          * shared process leaders.
  442                          */
  443                         fdtol = p1->p_fdtol;
  444                         FILEDESC_LOCK_FAST(p1->p_fd);
  445                         fdtol->fdl_refcount++;
  446                         FILEDESC_UNLOCK_FAST(p1->p_fd);
  447                 } else {
  448                         /* 
  449                          * Shared file descriptor table, and
  450                          * different process leaders 
  451                          */
  452                         fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
  453                                                          p1->p_fd,
  454                                                          p2);
  455                 }
  456         }
  457         /*
  458          * Make a proc table entry for the new process.
  459          * Start by zeroing the section of proc that is zero-initialized,
  460          * then copy the section that is copied directly from the parent.
  461          */
  462         td2 = FIRST_THREAD_IN_PROC(p2);
  463         kg2 = FIRST_KSEGRP_IN_PROC(p2);
  464 
  465         /* Allocate and switch to an alternate kstack if specified. */
  466         if (pages != 0)
  467                 vm_thread_new_altkstack(td2, pages);
  468 
  469         PROC_LOCK(p2);
  470         PROC_LOCK(p1);
  471 
  472         bzero(&td2->td_startzero,
  473             __rangeof(struct thread, td_startzero, td_endzero));
  474         bzero(&kg2->kg_startzero,
  475             __rangeof(struct ksegrp, kg_startzero, kg_endzero));
  476 
  477         bcopy(&td->td_startcopy, &td2->td_startcopy,
  478             __rangeof(struct thread, td_startcopy, td_endcopy));
  479         bcopy(&td->td_ksegrp->kg_startcopy, &kg2->kg_startcopy,
  480             __rangeof(struct ksegrp, kg_startcopy, kg_endcopy));
  481 
  482         td2->td_sigstk = td->td_sigstk;
  483         td2->td_sigmask = td->td_sigmask;
  484 
  485         /*
  486          * Duplicate sub-structures as needed.
  487          * Increase reference counts on shared objects.
  488          */
  489         p2->p_flag = 0;
  490         if (p1->p_flag & P_PROFIL)
  491                 startprofclock(p2);
  492         mtx_lock_spin(&sched_lock);
  493         p2->p_sflag = PS_INMEM;
  494         /*
  495          * Allow the scheduler to adjust the priority of the child and
  496          * parent while we hold the sched_lock.
  497          */
  498         sched_fork(td, td2);
  499 
  500         mtx_unlock_spin(&sched_lock);
  501         td2->td_ucred = crhold(p2->p_ucred);    /* XXXKSE */
  502 #ifdef AUDIT
  503         audit_proc_fork(p1, p2);
  504 #endif
  505         pargs_hold(p2->p_args);
  506 
  507         if (flags & RFSIGSHARE) {
  508                 p2->p_sigacts = sigacts_hold(p1->p_sigacts);
  509         } else {
  510                 sigacts_copy(newsigacts, p1->p_sigacts);
  511                 p2->p_sigacts = newsigacts;
  512         }
  513         if (flags & RFLINUXTHPN) 
  514                 p2->p_sigparent = SIGUSR1;
  515         else
  516                 p2->p_sigparent = SIGCHLD;
  517 
  518         p2->p_textvp = p1->p_textvp;
  519         p2->p_fd = fd;
  520         p2->p_fdtol = fdtol;
  521 
  522         /*
  523          * p_limit is copy-on-write.  Bump its refcount.
  524          */
  525         p2->p_limit = lim_hold(p1->p_limit);
  526 
  527         pstats_fork(p1->p_stats, p2->p_stats);
  528 
  529         PROC_UNLOCK(p1);
  530         PROC_UNLOCK(p2);
  531 
  532         /* Bump references to the text vnode (for procfs) */
  533         if (p2->p_textvp)
  534                 vref(p2->p_textvp);
  535 
  536         /*
  537          * Set up linkage for kernel based threading.
  538          */
  539         if ((flags & RFTHREAD) != 0) {
  540                 mtx_lock(&ppeers_lock);
  541                 p2->p_peers = p1->p_peers;
  542                 p1->p_peers = p2;
  543                 p2->p_leader = p1->p_leader;
  544                 mtx_unlock(&ppeers_lock);
  545                 PROC_LOCK(p1->p_leader);
  546                 if ((p1->p_leader->p_flag & P_WEXIT) != 0) {
  547                         PROC_UNLOCK(p1->p_leader);
  548                         /*
  549                          * The task leader is exiting, so process p1 is
  550                          * going to be killed shortly.  Since p1 obviously
  551                          * isn't dead yet, we know that the leader is either
  552                          * sending SIGKILL's to all the processes in this
  553                          * task or is sleeping waiting for all the peers to
  554                          * exit.  We let p1 complete the fork, but we need
  555                          * to go ahead and kill the new process p2 since
  556                          * the task leader may not get a chance to send
  557                          * SIGKILL to it.  We leave it on the list so that
  558                          * the task leader will wait for this new process
  559                          * to commit suicide.
  560                          */
  561                         PROC_LOCK(p2);
  562                         psignal(p2, SIGKILL);
  563                         PROC_UNLOCK(p2);
  564                 } else
  565                         PROC_UNLOCK(p1->p_leader);
  566         } else {
  567                 p2->p_peers = NULL;
  568                 p2->p_leader = p2;
  569         }
  570 
  571         sx_xlock(&proctree_lock);
  572         PGRP_LOCK(p1->p_pgrp);
  573         PROC_LOCK(p2);
  574         PROC_LOCK(p1);
  575 
  576         /*
  577          * Preserve some more flags in subprocess.  P_PROFIL has already
  578          * been preserved.
  579          */
  580         p2->p_flag |= p1->p_flag & P_SUGID;
  581         td2->td_pflags |= td->td_pflags & TDP_ALTSTACK;
  582         SESS_LOCK(p1->p_session);
  583         if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
  584                 p2->p_flag |= P_CONTROLT;
  585         SESS_UNLOCK(p1->p_session);
  586         if (flags & RFPPWAIT)
  587                 p2->p_flag |= P_PPWAIT;
  588 
  589         p2->p_pgrp = p1->p_pgrp;
  590         LIST_INSERT_AFTER(p1, p2, p_pglist);
  591         PGRP_UNLOCK(p1->p_pgrp);
  592         LIST_INIT(&p2->p_children);
  593 
  594         callout_init(&p2->p_itcallout, CALLOUT_MPSAFE);
  595 
  596 #ifdef KTRACE
  597         /*
  598          * Copy traceflag and tracefile if enabled.
  599          */
  600         mtx_lock(&ktrace_mtx);
  601         KASSERT(p2->p_tracevp == NULL, ("new process has a ktrace vnode"));
  602         if (p1->p_traceflag & KTRFAC_INHERIT) {
  603                 p2->p_traceflag = p1->p_traceflag;
  604                 if ((p2->p_tracevp = p1->p_tracevp) != NULL) {
  605                         VREF(p2->p_tracevp);
  606                         KASSERT(p1->p_tracecred != NULL,
  607                             ("ktrace vnode with no cred"));
  608                         p2->p_tracecred = crhold(p1->p_tracecred);
  609                 }
  610         }
  611         mtx_unlock(&ktrace_mtx);
  612 #endif
  613 
  614         /*
  615          * If PF_FORK is set, the child process inherits the
  616          * procfs ioctl flags from its parent.
  617          */
  618         if (p1->p_pfsflags & PF_FORK) {
  619                 p2->p_stops = p1->p_stops;
  620                 p2->p_pfsflags = p1->p_pfsflags;
  621         }
  622 
  623         /*
  624          * This begins the section where we must prevent the parent
  625          * from being swapped.
  626          */
  627         _PHOLD(p1);
  628         PROC_UNLOCK(p1);
  629 
  630         /*
  631          * Attach the new process to its parent.
  632          *
  633          * If RFNOWAIT is set, the newly created process becomes a child
  634          * of init.  This effectively disassociates the child from the
  635          * parent.
  636          */
  637         if (flags & RFNOWAIT)
  638                 pptr = initproc;
  639         else
  640                 pptr = p1;
  641         p2->p_pptr = pptr;
  642         LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
  643         sx_xunlock(&proctree_lock);
  644 
  645         /* Inform accounting that we have forked. */
  646         p2->p_acflag = AFORK;
  647         PROC_UNLOCK(p2);
  648 
  649         /*
  650          * Finish creating the child process.  It will return via a different
  651          * execution path later.  (ie: directly into user mode)
  652          */
  653         vm_forkproc(td, p2, td2, flags);
  654 
  655         if (flags == (RFFDG | RFPROC)) {
  656                 atomic_add_int(&cnt.v_forks, 1);
  657                 atomic_add_int(&cnt.v_forkpages, p2->p_vmspace->vm_dsize +
  658                     p2->p_vmspace->vm_ssize);
  659         } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
  660                 atomic_add_int(&cnt.v_vforks, 1);
  661                 atomic_add_int(&cnt.v_vforkpages, p2->p_vmspace->vm_dsize +
  662                     p2->p_vmspace->vm_ssize);
  663         } else if (p1 == &proc0) {
  664                 atomic_add_int(&cnt.v_kthreads, 1);
  665                 atomic_add_int(&cnt.v_kthreadpages, p2->p_vmspace->vm_dsize +
  666                     p2->p_vmspace->vm_ssize);
  667         } else {
  668                 atomic_add_int(&cnt.v_rforks, 1);
  669                 atomic_add_int(&cnt.v_rforkpages, p2->p_vmspace->vm_dsize +
  670                     p2->p_vmspace->vm_ssize);
  671         }
  672 
  673         /*
  674          * Both processes are set up, now check if any loadable modules want
  675          * to adjust anything.
  676          *   What if they have an error? XXX
  677          */
  678         EVENTHANDLER_INVOKE(process_fork, p1, p2, flags);
  679 
  680         /*
  681          * Set the child start time and mark the process as being complete.
  682          */
  683         microuptime(&p2->p_stats->p_start);
  684         mtx_lock_spin(&sched_lock);
  685         p2->p_state = PRS_NORMAL;
  686 
  687         /*
  688          * If RFSTOPPED not requested, make child runnable and add to
  689          * run queue.
  690          */
  691         if ((flags & RFSTOPPED) == 0) {
  692                 TD_SET_CAN_RUN(td2);
  693                 setrunqueue(td2, SRQ_BORING);
  694         }
  695         mtx_unlock_spin(&sched_lock);
  696 
  697         /*
  698          * Now can be swapped.
  699          */
  700         PROC_LOCK(p1);
  701         _PRELE(p1);
  702         PROC_UNLOCK(p1);
  703 
  704         /*
  705          * Tell any interested parties about the new process.
  706          */
  707         knote_fork(&p1->p_klist, p2->p_pid);
  708         /*
  709          * Preserve synchronization semantics of vfork.  If waiting for
  710          * child to exec or exit, set P_PPWAIT on child, and sleep on our
  711          * proc (in case of exit).
  712          */
  713         PROC_LOCK(p2);
  714         while (p2->p_flag & P_PPWAIT)
  715                 msleep(p1, &p2->p_mtx, PWAIT, "ppwait", 0);
  716         PROC_UNLOCK(p2);
  717 
  718         /*
  719          * Return child proc pointer to parent.
  720          */
  721         *procp = p2;
  722         return (0);
  723 fail:
  724         sx_sunlock(&proctree_lock);
  725         if (ppsratecheck(&lastfail, &curfail, 1))
  726                 printf("maxproc limit exceeded by uid %i, please see tuning(7) and login.conf(5).\n",
  727                     td->td_ucred->cr_ruid);
  728         sx_xunlock(&allproc_lock);
  729 #ifdef MAC
  730         mac_destroy_proc(newproc);
  731 #endif
  732 #ifdef AUDIT
  733         audit_proc_free(newproc);
  734 #endif
  735         uma_zfree(proc_zone, newproc);
  736         tsleep(&forksleep, PUSER, "fork", hz / 2);
  737         return (error);
  738 }
  739 
  740 /*
  741  * Handle the return of a child process from fork1().  This function
  742  * is called from the MD fork_trampoline() entry point.
  743  */
  744 void
  745 fork_exit(callout, arg, frame)
  746         void (*callout)(void *, struct trapframe *);
  747         void *arg;
  748         struct trapframe *frame;
  749 {
  750         struct proc *p;
  751         struct thread *td;
  752 
  753         /*
  754          * Finish setting up thread glue so that it begins execution in a
  755          * non-nested critical section with sched_lock held but not recursed.
  756          */
  757         td = curthread;
  758         p = td->td_proc;
  759         td->td_oncpu = PCPU_GET(cpuid);
  760         KASSERT(p->p_state == PRS_NORMAL, ("executing process is still new"));
  761 
  762         sched_lock.mtx_lock = (uintptr_t)td;
  763         mtx_assert(&sched_lock, MA_OWNED | MA_NOTRECURSED);
  764         CTR4(KTR_PROC, "fork_exit: new thread %p (kse %p, pid %d, %s)",
  765                 td, td->td_sched, p->p_pid, p->p_comm);
  766 
  767         /*
  768          * Processes normally resume in mi_switch() after being
  769          * cpu_switch()'ed to, but when children start up they arrive here
  770          * instead, so we must do much the same things as mi_switch() would.
  771          */
  772 
  773         if ((td = PCPU_GET(deadthread))) {
  774                 PCPU_SET(deadthread, NULL);
  775                 thread_stash(td);
  776         }
  777         td = curthread;
  778         mtx_unlock_spin(&sched_lock);
  779 
  780         /*
  781          * cpu_set_fork_handler intercepts this function call to
  782          * have this call a non-return function to stay in kernel mode.
  783          * initproc has its own fork handler, but it does return.
  784          */
  785         KASSERT(callout != NULL, ("NULL callout in fork_exit"));
  786         callout(arg, frame);
  787 
  788         /*
  789          * Check if a kernel thread misbehaved and returned from its main
  790          * function.
  791          */
  792         PROC_LOCK(p);
  793         if (p->p_flag & P_KTHREAD) {
  794                 PROC_UNLOCK(p);
  795                 printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
  796                     p->p_comm, p->p_pid);
  797                 kthread_exit(0);
  798         }
  799         PROC_UNLOCK(p);
  800         mtx_assert(&Giant, MA_NOTOWNED);
  801 }
  802 
  803 /*
  804  * Simplified back end of syscall(), used when returning from fork()
  805  * directly into user mode.  Giant is not held on entry, and must not
  806  * be held on return.  This function is passed in to fork_exit() as the
  807  * first parameter and is called when returning to a new userland process.
  808  */
  809 void
  810 fork_return(td, frame)
  811         struct thread *td;
  812         struct trapframe *frame;
  813 {
  814 
  815         userret(td, frame, 0);
  816 #ifdef KTRACE
  817         if (KTRPOINT(td, KTR_SYSRET))
  818                 ktrsysret(SYS_fork, 0, 0);
  819 #endif
  820         mtx_assert(&Giant, MA_NOTOWNED);
  821 }

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