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  * 3. All advertising materials mentioning features or use of this software
   19  *    must display the following acknowledgement:
   20  *      This product includes software developed by the University of
   21  *      California, Berkeley and its contributors.
   22  * 4. Neither the name of the University nor the names of its contributors
   23  *    may be used to endorse or promote products derived from this software
   24  *    without specific prior written permission.
   25  *
   26  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   27  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   28  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   29  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   30  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   31  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   32  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   33  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   34  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   35  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   36  * SUCH DAMAGE.
   37  *
   38  *      @(#)kern_fork.c 8.6 (Berkeley) 4/8/94
   39  */
   40 
   41 #include <sys/cdefs.h>
   42 __FBSDID("$FreeBSD: releng/5.2/sys/kern/kern_fork.c 121688 2003-10-29 15:23:09Z bde $");
   43 
   44 #include "opt_ktrace.h"
   45 #include "opt_mac.h"
   46 
   47 #include <sys/param.h>
   48 #include <sys/systm.h>
   49 #include <sys/sysproto.h>
   50 #include <sys/eventhandler.h>
   51 #include <sys/filedesc.h>
   52 #include <sys/kernel.h>
   53 #include <sys/kthread.h>
   54 #include <sys/sysctl.h>
   55 #include <sys/lock.h>
   56 #include <sys/malloc.h>
   57 #include <sys/mutex.h>
   58 #include <sys/proc.h>
   59 #include <sys/pioctl.h>
   60 #include <sys/resourcevar.h>
   61 #include <sys/sched.h>
   62 #include <sys/syscall.h>
   63 #include <sys/vmmeter.h>
   64 #include <sys/vnode.h>
   65 #include <sys/acct.h>
   66 #include <sys/mac.h>
   67 #include <sys/ktr.h>
   68 #include <sys/ktrace.h>
   69 #include <sys/unistd.h> 
   70 #include <sys/jail.h>
   71 #include <sys/sx.h>
   72 
   73 #include <vm/vm.h>
   74 #include <vm/pmap.h>
   75 #include <vm/vm_map.h>
   76 #include <vm/vm_extern.h>
   77 #include <vm/uma.h>
   78 
   79 #include <sys/user.h>
   80 #include <machine/critical.h>
   81 
   82 #ifndef _SYS_SYSPROTO_H_
   83 struct fork_args {
   84         int     dummy;
   85 };
   86 #endif
   87 
   88 static int forksleep; /* Place for fork1() to sleep on. */
   89 
   90 /*
   91  * MPSAFE
   92  */
   93 /* ARGSUSED */
   94 int
   95 fork(td, uap)
   96         struct thread *td;
   97         struct fork_args *uap;
   98 {
   99         int error;
  100         struct proc *p2;
  101 
  102         error = fork1(td, RFFDG | RFPROC, 0, &p2);
  103         if (error == 0) {
  104                 td->td_retval[0] = p2->p_pid;
  105                 td->td_retval[1] = 0;
  106         }
  107         return (error);
  108 }
  109 
  110 /*
  111  * MPSAFE
  112  */
  113 /* ARGSUSED */
  114 int
  115 vfork(td, uap)
  116         struct thread *td;
  117         struct vfork_args *uap;
  118 {
  119         int error;
  120         struct proc *p2;
  121 
  122         error = fork1(td, RFFDG | RFPROC | RFPPWAIT | RFMEM, 0, &p2);
  123         if (error == 0) {
  124                 td->td_retval[0] = p2->p_pid;
  125                 td->td_retval[1] = 0;
  126         }
  127         return (error);
  128 }
  129 
  130 /*
  131  * MPSAFE
  132  */
  133 int
  134 rfork(td, uap)
  135         struct thread *td;
  136         struct rfork_args *uap;
  137 {
  138         int error;
  139         struct proc *p2;
  140 
  141         /* Don't allow kernel only flags. */
  142         if ((uap->flags & RFKERNELONLY) != 0)
  143                 return (EINVAL);
  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         sysctl_wire_old_buffer(req, sizeof(int));
  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         uid_t uid;
  201         struct proc *newproc;
  202         int ok, trypid;
  203         static int curfail, pidchecked = 0;
  204         static struct timeval lastfail;
  205         struct filedesc *fd;
  206         struct filedesc_to_leader *fdtol;
  207         struct thread *td2;
  208         struct kse *ke2;
  209         struct ksegrp *kg2;
  210         struct sigacts *newsigacts;
  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         mtx_lock(&Giant);
  219 
  220         /*
  221          * Here we don't create a new process, but we divorce
  222          * certain parts of a process from itself.
  223          */
  224         if ((flags & RFPROC) == 0) {
  225                 vm_forkproc(td, NULL, NULL, flags);
  226 
  227                 /*
  228                  * Close all file descriptors.
  229                  */
  230                 if (flags & RFCFDG) {
  231                         struct filedesc *fdtmp;
  232                         fdtmp = fdinit(td->td_proc->p_fd);
  233                         fdfree(td);
  234                         p1->p_fd = fdtmp;
  235                 }
  236 
  237                 /*
  238                  * Unshare file descriptors (from parent.)
  239                  */
  240                 if (flags & RFFDG) {
  241                         FILEDESC_LOCK(p1->p_fd);
  242                         if (p1->p_fd->fd_refcnt > 1) {
  243                                 struct filedesc *newfd;
  244 
  245                                 newfd = fdcopy(td->td_proc->p_fd);
  246                                 FILEDESC_UNLOCK(p1->p_fd);
  247                                 fdfree(td);
  248                                 p1->p_fd = newfd;
  249                         } else
  250                                 FILEDESC_UNLOCK(p1->p_fd);
  251                 }
  252                 mtx_unlock(&Giant);
  253                 *procp = NULL;
  254                 return (0);
  255         }
  256 
  257         /*
  258          * Note 1:1 allows for forking with one thread coming out on the
  259          * other side with the expectation that the process is about to
  260          * exec.
  261          */
  262         if (p1->p_flag & P_SA) {
  263                 /*
  264                  * Idle the other threads for a second.
  265                  * Since the user space is copied, it must remain stable.
  266                  * In addition, all threads (from the user perspective)
  267                  * need to either be suspended or in the kernel,
  268                  * where they will try restart in the parent and will
  269                  * be aborted in the child.
  270                  */
  271                 PROC_LOCK(p1);
  272                 if (thread_single(SINGLE_NO_EXIT)) {
  273                         /* Abort.. someone else is single threading before us */
  274                         PROC_UNLOCK(p1);
  275                         mtx_unlock(&Giant);
  276                         return (ERESTART);
  277                 }
  278                 PROC_UNLOCK(p1);
  279                 /*
  280                  * All other activity in this process
  281                  * is now suspended at the user boundary,
  282                  * (or other safe places if we think of any).
  283                  */
  284         }
  285 
  286         /* Allocate new proc. */
  287         newproc = uma_zalloc(proc_zone, M_WAITOK);
  288 #ifdef MAC
  289         mac_init_proc(newproc);
  290 #endif
  291 
  292         /*
  293          * Although process entries are dynamically created, we still keep
  294          * a global limit on the maximum number we will create.  Don't allow
  295          * a nonprivileged user to use the last ten processes; don't let root
  296          * exceed the limit. The variable nprocs is the current number of
  297          * processes, maxproc is the limit.
  298          */
  299         sx_xlock(&allproc_lock);
  300         uid = td->td_ucred->cr_ruid;
  301         if ((nprocs >= maxproc - 10 && uid != 0) || nprocs >= maxproc) {
  302                 error = EAGAIN;
  303                 goto fail;
  304         }
  305 
  306         /*
  307          * Increment the count of procs running with this uid. Don't allow
  308          * a nonprivileged user to exceed their current limit.
  309          */
  310         PROC_LOCK(p1);
  311         ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1,
  312                 (uid != 0) ? p1->p_rlimit[RLIMIT_NPROC].rlim_cur : 0);
  313         PROC_UNLOCK(p1);
  314         if (!ok) {
  315                 error = EAGAIN;
  316                 goto fail;
  317         }
  318 
  319         /*
  320          * Increment the nprocs resource before blocking can occur.  There
  321          * are hard-limits as to the number of processes that can run.
  322          */
  323         nprocs++;
  324 
  325         /*
  326          * Find an unused process ID.  We remember a range of unused IDs
  327          * ready to use (from lastpid+1 through pidchecked-1).
  328          *
  329          * If RFHIGHPID is set (used during system boot), do not allocate
  330          * low-numbered pids.
  331          */
  332         trypid = lastpid + 1;
  333         if (flags & RFHIGHPID) {
  334                 if (trypid < 10)
  335                         trypid = 10;
  336         } else {
  337                 if (randompid)
  338                         trypid += arc4random() % randompid;
  339         }
  340 retry:
  341         /*
  342          * If the process ID prototype has wrapped around,
  343          * restart somewhat above 0, as the low-numbered procs
  344          * tend to include daemons that don't exit.
  345          */
  346         if (trypid >= PID_MAX) {
  347                 trypid = trypid % PID_MAX;
  348                 if (trypid < 100)
  349                         trypid += 100;
  350                 pidchecked = 0;
  351         }
  352         if (trypid >= pidchecked) {
  353                 int doingzomb = 0;
  354 
  355                 pidchecked = PID_MAX;
  356                 /*
  357                  * Scan the active and zombie procs to check whether this pid
  358                  * is in use.  Remember the lowest pid that's greater
  359                  * than trypid, so we can avoid checking for a while.
  360                  */
  361                 p2 = LIST_FIRST(&allproc);
  362 again:
  363                 for (; p2 != NULL; p2 = LIST_NEXT(p2, p_list)) {
  364                         PROC_LOCK(p2);
  365                         while (p2->p_pid == trypid ||
  366                             p2->p_pgrp->pg_id == trypid ||
  367                             p2->p_session->s_sid == trypid) {
  368                                 trypid++;
  369                                 if (trypid >= pidchecked) {
  370                                         PROC_UNLOCK(p2);
  371                                         goto retry;
  372                                 }
  373                         }
  374                         if (p2->p_pid > trypid && pidchecked > p2->p_pid)
  375                                 pidchecked = p2->p_pid;
  376                         if (p2->p_pgrp->pg_id > trypid &&
  377                             pidchecked > p2->p_pgrp->pg_id)
  378                                 pidchecked = p2->p_pgrp->pg_id;
  379                         if (p2->p_session->s_sid > trypid &&
  380                             pidchecked > p2->p_session->s_sid)
  381                                 pidchecked = p2->p_session->s_sid;
  382                         PROC_UNLOCK(p2);
  383                 }
  384                 if (!doingzomb) {
  385                         doingzomb = 1;
  386                         p2 = LIST_FIRST(&zombproc);
  387                         goto again;
  388                 }
  389         }
  390 
  391         /*
  392          * RFHIGHPID does not mess with the lastpid counter during boot.
  393          */
  394         if (flags & RFHIGHPID)
  395                 pidchecked = 0;
  396         else
  397                 lastpid = trypid;
  398 
  399         p2 = newproc;
  400         p2->p_state = PRS_NEW;          /* protect against others */
  401         p2->p_pid = trypid;
  402         LIST_INSERT_HEAD(&allproc, p2, p_list);
  403         LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
  404         sx_xunlock(&allproc_lock);
  405 
  406         /*
  407          * Malloc things while we don't hold any locks.
  408          */
  409         if (flags & RFSIGSHARE)
  410                 newsigacts = NULL;
  411         else
  412                 newsigacts = sigacts_alloc();
  413 
  414         /*
  415          * Copy filedesc.
  416          */
  417         if (flags & RFCFDG) {
  418                 fd = fdinit(td->td_proc->p_fd);
  419                 fdtol = NULL;
  420         } else if (flags & RFFDG) {
  421                 FILEDESC_LOCK(p1->p_fd);
  422                 fd = fdcopy(td->td_proc->p_fd);
  423                 FILEDESC_UNLOCK(p1->p_fd);
  424                 fdtol = NULL;
  425         } else {
  426                 fd = fdshare(p1->p_fd);
  427                 if (p1->p_fdtol == NULL)
  428                         p1->p_fdtol =
  429                                 filedesc_to_leader_alloc(NULL,
  430                                                          NULL,
  431                                                          p1->p_leader);
  432                 if ((flags & RFTHREAD) != 0) {
  433                         /*
  434                          * Shared file descriptor table and
  435                          * shared process leaders.
  436                          */
  437                         fdtol = p1->p_fdtol;
  438                         FILEDESC_LOCK(p1->p_fd);
  439                         fdtol->fdl_refcount++;
  440                         FILEDESC_UNLOCK(p1->p_fd);
  441                 } else {
  442                         /* 
  443                          * Shared file descriptor table, and
  444                          * different process leaders 
  445                          */
  446                         fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
  447                                                          p1->p_fd,
  448                                                          p2);
  449                 }
  450         }
  451         /*
  452          * Make a proc table entry for the new process.
  453          * Start by zeroing the section of proc that is zero-initialized,
  454          * then copy the section that is copied directly from the parent.
  455          */
  456         td2 = FIRST_THREAD_IN_PROC(p2);
  457         kg2 = FIRST_KSEGRP_IN_PROC(p2);
  458         ke2 = FIRST_KSE_IN_KSEGRP(kg2);
  459 
  460         /* Allocate and switch to an alternate kstack if specified */
  461         if (pages != 0)
  462                 vm_thread_new_altkstack(td2, pages);
  463 
  464         PROC_LOCK(p2);
  465         PROC_LOCK(p1);
  466 
  467 #define RANGEOF(type, start, end) (offsetof(type, end) - offsetof(type, start))
  468 
  469         bzero(&p2->p_startzero,
  470             (unsigned) RANGEOF(struct proc, p_startzero, p_endzero));
  471         bzero(&ke2->ke_startzero,
  472             (unsigned) RANGEOF(struct kse, ke_startzero, ke_endzero));
  473         bzero(&td2->td_startzero,
  474             (unsigned) RANGEOF(struct thread, td_startzero, td_endzero));
  475         bzero(&kg2->kg_startzero,
  476             (unsigned) RANGEOF(struct ksegrp, kg_startzero, kg_endzero));
  477 
  478         bcopy(&p1->p_startcopy, &p2->p_startcopy,
  479             (unsigned) RANGEOF(struct proc, p_startcopy, p_endcopy));
  480         bcopy(&td->td_startcopy, &td2->td_startcopy,
  481             (unsigned) RANGEOF(struct thread, td_startcopy, td_endcopy));
  482         bcopy(&td->td_ksegrp->kg_startcopy, &kg2->kg_startcopy,
  483             (unsigned) RANGEOF(struct ksegrp, kg_startcopy, kg_endcopy));
  484 #undef RANGEOF
  485 
  486         /* Set up the thread as an active thread (as if runnable). */
  487         ke2->ke_state = KES_THREAD;
  488         ke2->ke_thread = td2;
  489         td2->td_kse = ke2;
  490 
  491         /*
  492          * Duplicate sub-structures as needed.
  493          * Increase reference counts on shared objects.
  494          * The p_stats substruct is set in vm_forkproc.
  495          */
  496         p2->p_flag = 0;
  497         if (p1->p_flag & P_PROFIL)
  498                 startprofclock(p2);
  499         mtx_lock_spin(&sched_lock);
  500         p2->p_sflag = PS_INMEM;
  501         /*
  502          * Allow the scheduler to adjust the priority of the child and
  503          * parent while we hold the sched_lock.
  504          */
  505         sched_fork(p1, p2);
  506 
  507         mtx_unlock_spin(&sched_lock);
  508         p2->p_ucred = crhold(td->td_ucred);
  509         td2->td_ucred = crhold(p2->p_ucred);    /* XXXKSE */
  510 
  511         pargs_hold(p2->p_args);
  512 
  513         if (flags & RFSIGSHARE) {
  514                 p2->p_sigacts = sigacts_hold(p1->p_sigacts);
  515         } else {
  516                 sigacts_copy(newsigacts, p1->p_sigacts);
  517                 p2->p_sigacts = newsigacts;
  518         }
  519         if (flags & RFLINUXTHPN) 
  520                 p2->p_sigparent = SIGUSR1;
  521         else
  522                 p2->p_sigparent = SIGCHLD;
  523 
  524         /* Bump references to the text vnode (for procfs) */
  525         p2->p_textvp = p1->p_textvp;
  526         if (p2->p_textvp)
  527                 VREF(p2->p_textvp);
  528         p2->p_fd = fd;
  529         p2->p_fdtol = fdtol;
  530         PROC_UNLOCK(p1);
  531         PROC_UNLOCK(p2);
  532 
  533         /*
  534          * p_limit is copy-on-write, bump refcnt,
  535          */
  536         p2->p_limit = p1->p_limit;
  537         p2->p_limit->p_refcnt++;
  538 
  539         /*
  540          * Setup linkage for kernel based threading
  541          */
  542         if((flags & RFTHREAD) != 0) {
  543                 mtx_lock(&ppeers_lock);
  544                 p2->p_peers = p1->p_peers;
  545                 p1->p_peers = p2;
  546                 p2->p_leader = p1->p_leader;
  547                 mtx_unlock(&ppeers_lock);
  548                 PROC_LOCK(p1->p_leader);
  549                 if ((p1->p_leader->p_flag & P_WEXIT) != 0) {
  550                         PROC_UNLOCK(p1->p_leader);
  551                         /*
  552                          * The task leader is exiting, so process p1 is
  553                          * going to be killed shortly.  Since p1 obviously
  554                          * isn't dead yet, we know that the leader is either
  555                          * sending SIGKILL's to all the processes in this
  556                          * task or is sleeping waiting for all the peers to
  557                          * exit.  We let p1 complete the fork, but we need
  558                          * to go ahead and kill the new process p2 since
  559                          * the task leader may not get a chance to send
  560                          * SIGKILL to it.  We leave it on the list so that
  561                          * the task leader will wait for this new process
  562                          * to commit suicide.
  563                          */
  564                         PROC_LOCK(p2);
  565                         psignal(p2, SIGKILL);
  566                         PROC_UNLOCK(p2);
  567                 } else
  568                         PROC_UNLOCK(p1->p_leader);
  569         } else {
  570                 p2->p_peers = NULL;
  571                 p2->p_leader = p2;
  572         }
  573 
  574         sx_xlock(&proctree_lock);
  575         PGRP_LOCK(p1->p_pgrp);
  576         PROC_LOCK(p2);
  577         PROC_LOCK(p1);
  578 
  579         /*
  580          * Preserve some more flags in subprocess.  P_PROFIL has already
  581          * been preserved.
  582          */
  583         p2->p_flag |= p1->p_flag & (P_ALTSTACK | P_SUGID);
  584         SESS_LOCK(p1->p_session);
  585         if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
  586                 p2->p_flag |= P_CONTROLT;
  587         SESS_UNLOCK(p1->p_session);
  588         if (flags & RFPPWAIT)
  589                 p2->p_flag |= P_PPWAIT;
  590 
  591         LIST_INSERT_AFTER(p1, p2, p_pglist);
  592         PGRP_UNLOCK(p1->p_pgrp);
  593         LIST_INIT(&p2->p_children);
  594 
  595         callout_init(&p2->p_itcallout, CALLOUT_MPSAFE);
  596 
  597 #ifdef KTRACE
  598         /*
  599          * Copy traceflag and tracefile if enabled.
  600          */
  601         mtx_lock(&ktrace_mtx);
  602         KASSERT(p2->p_tracevp == NULL, ("new process has a ktrace vnode"));
  603         if (p1->p_traceflag & KTRFAC_INHERIT) {
  604                 p2->p_traceflag = p1->p_traceflag;
  605                 if ((p2->p_tracevp = p1->p_tracevp) != NULL) {
  606                         VREF(p2->p_tracevp);
  607                         KASSERT(p1->p_tracecred != NULL,
  608                             ("ktrace vnode with no cred"));
  609                         p2->p_tracecred = crhold(p1->p_tracecred);
  610                 }
  611         }
  612         mtx_unlock(&ktrace_mtx);
  613 #endif
  614 
  615         /*
  616          * If PF_FORK is set, the child process inherits the
  617          * procfs ioctl flags from its parent.
  618          */
  619         if (p1->p_pfsflags & PF_FORK) {
  620                 p2->p_stops = p1->p_stops;
  621                 p2->p_pfsflags = p1->p_pfsflags;
  622         }
  623 
  624         /*
  625          * This begins the section where we must prevent the parent
  626          * from being swapped.
  627          */
  628         _PHOLD(p1);
  629         PROC_UNLOCK(p1);
  630 
  631         /*
  632          * Attach the new process to its parent.
  633          *
  634          * If RFNOWAIT is set, the newly created process becomes a child
  635          * of init.  This effectively disassociates the child from the
  636          * parent.
  637          */
  638         if (flags & RFNOWAIT)
  639                 pptr = initproc;
  640         else
  641                 pptr = p1;
  642         p2->p_pptr = pptr;
  643         LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
  644         sx_xunlock(&proctree_lock);
  645 
  646         /* Inform accounting that we have forked. */
  647         p2->p_acflag = AFORK;
  648         PROC_UNLOCK(p2);
  649 
  650         /*
  651          * Finish creating the child process.  It will return via a different
  652          * execution path later.  (ie: directly into user mode)
  653          */
  654         vm_forkproc(td, p2, td2, flags);
  655 
  656         if (flags == (RFFDG | RFPROC)) {
  657                 cnt.v_forks++;
  658                 cnt.v_forkpages += p2->p_vmspace->vm_dsize +
  659                     p2->p_vmspace->vm_ssize;
  660         } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
  661                 cnt.v_vforks++;
  662                 cnt.v_vforkpages += p2->p_vmspace->vm_dsize +
  663                     p2->p_vmspace->vm_ssize;
  664         } else if (p1 == &proc0) {
  665                 cnt.v_kthreads++;
  666                 cnt.v_kthreadpages += p2->p_vmspace->vm_dsize +
  667                     p2->p_vmspace->vm_ssize;
  668         } else {
  669                 cnt.v_rforks++;
  670                 cnt.v_rforkpages += p2->p_vmspace->vm_dsize +
  671                     p2->p_vmspace->vm_ssize;
  672         }
  673 
  674         /*
  675          * Both processes are set up, now check if any loadable modules want
  676          * to adjust anything.
  677          *   What if they have an error? XXX
  678          */
  679         EVENTHANDLER_INVOKE(process_fork, p1, p2, flags);
  680 
  681         /*
  682          * If RFSTOPPED not requested, make child runnable and add to
  683          * run queue.
  684          */
  685         microuptime(&p2->p_stats->p_start);
  686         if ((flags & RFSTOPPED) == 0) {
  687                 mtx_lock_spin(&sched_lock);
  688                 p2->p_state = PRS_NORMAL;
  689                 TD_SET_CAN_RUN(td2);
  690                 setrunqueue(td2);
  691                 mtx_unlock_spin(&sched_lock);
  692         }
  693 
  694         /*
  695          * Now can be swapped.
  696          */
  697         PROC_LOCK(p1);
  698         _PRELE(p1);
  699 
  700         /*
  701          * Tell any interested parties about the new process.
  702          */
  703         KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid);
  704 
  705         PROC_UNLOCK(p1);
  706 
  707         /*
  708          * Preserve synchronization semantics of vfork.  If waiting for
  709          * child to exec or exit, set P_PPWAIT on child, and sleep on our
  710          * proc (in case of exit).
  711          */
  712         PROC_LOCK(p2);
  713         while (p2->p_flag & P_PPWAIT)
  714                 msleep(p1, &p2->p_mtx, PWAIT, "ppwait", 0);
  715         PROC_UNLOCK(p2);
  716 
  717         /*
  718          * If other threads are waiting, let them continue now
  719          */
  720         if (p1->p_flag & P_SA) {
  721                 PROC_LOCK(p1);
  722                 thread_single_end();
  723                 PROC_UNLOCK(p1);
  724         }
  725 
  726         /*
  727          * Return child proc pointer to parent.
  728          */
  729         mtx_unlock(&Giant);
  730         *procp = p2;
  731         return (0);
  732 fail:
  733         if (ppsratecheck(&lastfail, &curfail, 1))
  734                 printf("maxproc limit exceeded by uid %i, please see tuning(7) and login.conf(5).\n",
  735                         uid);
  736         sx_xunlock(&allproc_lock);
  737         uma_zfree(proc_zone, newproc);
  738         if (p1->p_flag & P_SA) {
  739                 PROC_LOCK(p1);
  740                 thread_single_end();
  741                 PROC_UNLOCK(p1);
  742         }
  743         tsleep(&forksleep, PUSER, "fork", hz / 2);
  744         mtx_unlock(&Giant);
  745         return (error);
  746 }
  747 
  748 /*
  749  * Handle the return of a child process from fork1().  This function
  750  * is called from the MD fork_trampoline() entry point.
  751  */
  752 void
  753 fork_exit(callout, arg, frame)
  754         void (*callout)(void *, struct trapframe *);
  755         void *arg;
  756         struct trapframe *frame;
  757 {
  758         struct proc *p;
  759         struct thread *td;
  760 
  761         /*
  762          * Processes normally resume in mi_switch() after being
  763          * cpu_switch()'ed to, but when children start up they arrive here
  764          * instead, so we must do much the same things as mi_switch() would.
  765          */
  766 
  767         if ((td = PCPU_GET(deadthread))) {
  768                 PCPU_SET(deadthread, NULL);
  769                 thread_stash(td);
  770         }
  771         td = curthread;
  772         p = td->td_proc;
  773         td->td_oncpu = PCPU_GET(cpuid);
  774         p->p_state = PRS_NORMAL;
  775 
  776         /*
  777          * Finish setting up thread glue so that it begins execution in a
  778          * non-nested critical section with sched_lock held but not recursed.
  779          */
  780         sched_lock.mtx_lock = (uintptr_t)td;
  781         mtx_assert(&sched_lock, MA_OWNED | MA_NOTRECURSED);
  782         cpu_critical_fork_exit();
  783         CTR3(KTR_PROC, "fork_exit: new thread %p (pid %d, %s)", td, p->p_pid,
  784             p->p_comm);
  785         mtx_unlock_spin(&sched_lock);
  786 
  787         /*
  788          * cpu_set_fork_handler intercepts this function call to
  789          * have this call a non-return function to stay in kernel mode.
  790          * initproc has its own fork handler, but it does return.
  791          */
  792         KASSERT(callout != NULL, ("NULL callout in fork_exit"));
  793         callout(arg, frame);
  794 
  795         /*
  796          * Check if a kernel thread misbehaved and returned from its main
  797          * function.
  798          */
  799         PROC_LOCK(p);
  800         if (p->p_flag & P_KTHREAD) {
  801                 PROC_UNLOCK(p);
  802                 mtx_lock(&Giant);
  803                 printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
  804                     p->p_comm, p->p_pid);
  805                 kthread_exit(0);
  806         }
  807         PROC_UNLOCK(p);
  808 #ifdef DIAGNOSTIC
  809         cred_free_thread(td);
  810 #endif
  811         mtx_assert(&Giant, MA_NOTOWNED);
  812 }
  813 
  814 /*
  815  * Simplified back end of syscall(), used when returning from fork()
  816  * directly into user mode.  Giant is not held on entry, and must not
  817  * be held on return.  This function is passed in to fork_exit() as the
  818  * first parameter and is called when returning to a new userland process.
  819  */
  820 void
  821 fork_return(td, frame)
  822         struct thread *td;
  823         struct trapframe *frame;
  824 {
  825 
  826         userret(td, frame, 0);
  827 #ifdef KTRACE
  828         if (KTRPOINT(td, KTR_SYSRET))
  829                 ktrsysret(SYS_fork, 0, 0);
  830 #endif
  831         mtx_assert(&Giant, MA_NOTOWNED);
  832 }

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