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: releng/5.4/sys/kern/kern_fork.c 145645 2005-04-28 23:37:19Z davidxu $");
   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 <vm/vm.h>
   70 #include <vm/pmap.h>
   71 #include <vm/vm_map.h>
   72 #include <vm/vm_extern.h>
   73 #include <vm/uma.h>
   74 
   75 #include <machine/critical.h>
   76 
   77 #ifndef _SYS_SYSPROTO_H_
   78 struct fork_args {
   79         int     dummy;
   80 };
   81 #endif
   82 
   83 static int forksleep; /* Place for fork1() to sleep on. */
   84 
   85 /*
   86  * MPSAFE
   87  */
   88 /* ARGSUSED */
   89 int
   90 fork(td, uap)
   91         struct thread *td;
   92         struct fork_args *uap;
   93 {
   94         int error;
   95         struct proc *p2;
   96 
   97         error = fork1(td, RFFDG | RFPROC, 0, &p2);
   98         if (error == 0) {
   99                 td->td_retval[0] = p2->p_pid;
  100                 td->td_retval[1] = 0;
  101         }
  102         return (error);
  103 }
  104 
  105 /*
  106  * MPSAFE
  107  */
  108 /* ARGSUSED */
  109 int
  110 vfork(td, uap)
  111         struct thread *td;
  112         struct vfork_args *uap;
  113 {
  114         int error;
  115         struct proc *p2;
  116 
  117         error = fork1(td, RFFDG | RFPROC | RFPPWAIT | RFMEM, 0, &p2);
  118         if (error == 0) {
  119                 td->td_retval[0] = p2->p_pid;
  120                 td->td_retval[1] = 0;
  121         }
  122         return (error);
  123 }
  124 
  125 /*
  126  * MPSAFE
  127  */
  128 int
  129 rfork(td, uap)
  130         struct thread *td;
  131         struct rfork_args *uap;
  132 {
  133         struct proc *p2;
  134         int error;
  135 
  136         /* Don't allow kernel-only flags. */
  137         if ((uap->flags & RFKERNELONLY) != 0)
  138                 return (EINVAL);
  139 
  140         error = fork1(td, uap->flags, 0, &p2);
  141         if (error == 0) {
  142                 td->td_retval[0] = p2 ? p2->p_pid : 0;
  143                 td->td_retval[1] = 0;
  144         }
  145         return (error);
  146 }
  147 
  148 int     nprocs = 1;             /* process 0 */
  149 int     lastpid = 0;
  150 SYSCTL_INT(_kern, OID_AUTO, lastpid, CTLFLAG_RD, &lastpid, 0, 
  151     "Last used PID");
  152 
  153 /*
  154  * Random component to lastpid generation.  We mix in a random factor to make
  155  * it a little harder to predict.  We sanity check the modulus value to avoid
  156  * doing it in critical paths.  Don't let it be too small or we pointlessly
  157  * waste randomness entropy, and don't let it be impossibly large.  Using a
  158  * modulus that is too big causes a LOT more process table scans and slows
  159  * down fork processing as the pidchecked caching is defeated.
  160  */
  161 static int randompid = 0;
  162 
  163 static int
  164 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
  165 {
  166         int error, pid;
  167 
  168         error = sysctl_wire_old_buffer(req, sizeof(int));
  169         if (error != 0)
  170                 return(error);
  171         sx_xlock(&allproc_lock);
  172         pid = randompid;
  173         error = sysctl_handle_int(oidp, &pid, 0, req);
  174         if (error == 0 && req->newptr != NULL) {
  175                 if (pid < 0 || pid > PID_MAX - 100)     /* out of range */
  176                         pid = PID_MAX - 100;
  177                 else if (pid < 2)                       /* NOP */
  178                         pid = 0;
  179                 else if (pid < 100)                     /* Make it reasonable */
  180                         pid = 100;
  181                 randompid = pid;
  182         }
  183         sx_xunlock(&allproc_lock);
  184         return (error);
  185 }
  186 
  187 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
  188     0, 0, sysctl_kern_randompid, "I", "Random PID modulus");
  189 
  190 int
  191 fork1(td, flags, pages, procp)
  192         struct thread *td;
  193         int flags;
  194         int pages;
  195         struct proc **procp;
  196 {
  197         struct proc *p1, *p2, *pptr;
  198         uid_t uid;
  199         struct proc *newproc;
  200         int ok, trypid;
  201         static int curfail, pidchecked = 0;
  202         static struct timeval lastfail;
  203         struct filedesc *fd;
  204         struct filedesc_to_leader *fdtol;
  205         struct thread *td2;
  206         struct ksegrp *kg2;
  207         struct sigacts *newsigacts;
  208         int error;
  209 
  210         /* Can't copy and clear. */
  211         if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
  212                 return (EINVAL);
  213 
  214         p1 = td->td_proc;
  215 
  216         /*
  217          * Here we don't create a new process, but we divorce
  218          * certain parts of a process from itself.
  219          */
  220         if ((flags & RFPROC) == 0) {
  221                 vm_forkproc(td, NULL, NULL, flags);
  222 
  223                 /*
  224                  * Close all file descriptors.
  225                  */
  226                 if (flags & RFCFDG) {
  227                         struct filedesc *fdtmp;
  228                         fdtmp = fdinit(td->td_proc->p_fd);
  229                         fdfree(td);
  230                         p1->p_fd = fdtmp;
  231                 }
  232 
  233                 /*
  234                  * Unshare file descriptors (from parent).
  235                  */
  236                 if (flags & RFFDG) 
  237                         fdunshare(p1, td);
  238                 *procp = NULL;
  239                 return (0);
  240         }
  241 
  242         /*
  243          * Note 1:1 allows for forking with one thread coming out on the
  244          * other side with the expectation that the process is about to
  245          * exec.
  246          */
  247         if (p1->p_flag & P_HADTHREADS) {
  248                 /*
  249                  * Idle the other threads for a second.
  250                  * Since the user space is copied, it must remain stable.
  251                  * In addition, all threads (from the user perspective)
  252                  * need to either be suspended or in the kernel,
  253                  * where they will try restart in the parent and will
  254                  * be aborted in the child.
  255                  */
  256                 PROC_LOCK(p1);
  257                 if (thread_single(SINGLE_NO_EXIT)) {
  258                         /* Abort. Someone else is single threading before us. */
  259                         PROC_UNLOCK(p1);
  260                         return (ERESTART);
  261                 }
  262                 PROC_UNLOCK(p1);
  263                 /*
  264                  * All other activity in this process
  265                  * is now suspended at the user boundary,
  266                  * (or other safe places if we think of any).
  267                  */
  268         }
  269 
  270         /* Allocate new proc. */
  271         newproc = uma_zalloc(proc_zone, M_WAITOK);
  272 #ifdef MAC
  273         mac_init_proc(newproc);
  274 #endif
  275         knlist_init(&newproc->p_klist, &newproc->p_mtx);
  276 
  277         /* We have to lock the process tree while we look for a pid. */
  278         sx_slock(&proctree_lock);
  279 
  280         /*
  281          * Although process entries are dynamically created, we still keep
  282          * a global limit on the maximum number we will create.  Don't allow
  283          * a nonprivileged user to use the last ten processes; don't let root
  284          * exceed the limit. The variable nprocs is the current number of
  285          * processes, maxproc is the limit.
  286          */
  287         sx_xlock(&allproc_lock);
  288         uid = td->td_ucred->cr_ruid;
  289         if ((nprocs >= maxproc - 10 &&
  290             suser_cred(td->td_ucred, SUSER_RUID) != 0) ||
  291             nprocs >= maxproc) {
  292                 error = EAGAIN;
  293                 goto fail;
  294         }
  295 
  296         /*
  297          * Increment the count of procs running with this uid. Don't allow
  298          * a nonprivileged user to exceed their current limit.
  299          */
  300         PROC_LOCK(p1);
  301         ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1,
  302                 (uid != 0) ? lim_cur(p1, RLIMIT_NPROC) : 0);
  303         PROC_UNLOCK(p1);
  304         if (!ok) {
  305                 error = EAGAIN;
  306                 goto fail;
  307         }
  308 
  309         /*
  310          * Increment the nprocs resource before blocking can occur.  There
  311          * are hard-limits as to the number of processes that can run.
  312          */
  313         nprocs++;
  314 
  315         /*
  316          * Find an unused process ID.  We remember a range of unused IDs
  317          * ready to use (from lastpid+1 through pidchecked-1).
  318          *
  319          * If RFHIGHPID is set (used during system boot), do not allocate
  320          * low-numbered pids.
  321          */
  322         trypid = lastpid + 1;
  323         if (flags & RFHIGHPID) {
  324                 if (trypid < 10)
  325                         trypid = 10;
  326         } else {
  327                 if (randompid)
  328                         trypid += arc4random() % randompid;
  329         }
  330 retry:
  331         /*
  332          * If the process ID prototype has wrapped around,
  333          * restart somewhat above 0, as the low-numbered procs
  334          * tend to include daemons that don't exit.
  335          */
  336         if (trypid >= PID_MAX) {
  337                 trypid = trypid % PID_MAX;
  338                 if (trypid < 100)
  339                         trypid += 100;
  340                 pidchecked = 0;
  341         }
  342         if (trypid >= pidchecked) {
  343                 int doingzomb = 0;
  344 
  345                 pidchecked = PID_MAX;
  346                 /*
  347                  * Scan the active and zombie procs to check whether this pid
  348                  * is in use.  Remember the lowest pid that's greater
  349                  * than trypid, so we can avoid checking for a while.
  350                  */
  351                 p2 = LIST_FIRST(&allproc);
  352 again:
  353                 for (; p2 != NULL; p2 = LIST_NEXT(p2, p_list)) {
  354                         PROC_LOCK(p2);
  355                         while (p2->p_pid == trypid ||
  356                             (p2->p_pgrp != NULL &&
  357                             (p2->p_pgrp->pg_id == trypid ||
  358                             (p2->p_session != NULL &&
  359                             p2->p_session->s_sid == trypid)))) {
  360                                 trypid++;
  361                                 if (trypid >= pidchecked) {
  362                                         PROC_UNLOCK(p2);
  363                                         goto retry;
  364                                 }
  365                         }
  366                         if (p2->p_pid > trypid && pidchecked > p2->p_pid)
  367                                 pidchecked = p2->p_pid;
  368                         if (p2->p_pgrp != NULL) {
  369                                 if (p2->p_pgrp->pg_id > trypid &&
  370                                     pidchecked > p2->p_pgrp->pg_id)
  371                                         pidchecked = p2->p_pgrp->pg_id;
  372                                 if (p2->p_session != NULL &&
  373                                     p2->p_session->s_sid > trypid &&
  374                                     pidchecked > p2->p_session->s_sid)
  375                                         pidchecked = p2->p_session->s_sid;
  376                         }
  377                         PROC_UNLOCK(p2);
  378                 }
  379                 if (!doingzomb) {
  380                         doingzomb = 1;
  381                         p2 = LIST_FIRST(&zombproc);
  382                         goto again;
  383                 }
  384         }
  385         sx_sunlock(&proctree_lock);
  386 
  387         /*
  388          * RFHIGHPID does not mess with the lastpid counter during boot.
  389          */
  390         if (flags & RFHIGHPID)
  391                 pidchecked = 0;
  392         else
  393                 lastpid = trypid;
  394 
  395         p2 = newproc;
  396         p2->p_state = PRS_NEW;          /* protect against others */
  397         p2->p_pid = trypid;
  398         LIST_INSERT_HEAD(&allproc, p2, p_list);
  399         LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
  400         sx_xunlock(&allproc_lock);
  401 
  402         /*
  403          * Malloc things while we don't hold any locks.
  404          */
  405         if (flags & RFSIGSHARE)
  406                 newsigacts = NULL;
  407         else
  408                 newsigacts = sigacts_alloc();
  409 
  410         /*
  411          * Copy filedesc.
  412          */
  413         if (flags & RFCFDG) {
  414                 fd = fdinit(p1->p_fd);
  415                 fdtol = NULL;
  416         } else if (flags & RFFDG) {
  417                 fd = fdcopy(p1->p_fd);
  418                 fdtol = NULL;
  419         } else {
  420                 fd = fdshare(p1->p_fd);
  421                 if (p1->p_fdtol == NULL)
  422                         p1->p_fdtol =
  423                                 filedesc_to_leader_alloc(NULL,
  424                                                          NULL,
  425                                                          p1->p_leader);
  426                 if ((flags & RFTHREAD) != 0) {
  427                         /*
  428                          * Shared file descriptor table and
  429                          * shared process leaders.
  430                          */
  431                         fdtol = p1->p_fdtol;
  432                         FILEDESC_LOCK_FAST(p1->p_fd);
  433                         fdtol->fdl_refcount++;
  434                         FILEDESC_UNLOCK_FAST(p1->p_fd);
  435                 } else {
  436                         /* 
  437                          * Shared file descriptor table, and
  438                          * different process leaders 
  439                          */
  440                         fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
  441                                                          p1->p_fd,
  442                                                          p2);
  443                 }
  444         }
  445         /*
  446          * Make a proc table entry for the new process.
  447          * Start by zeroing the section of proc that is zero-initialized,
  448          * then copy the section that is copied directly from the parent.
  449          */
  450         td2 = FIRST_THREAD_IN_PROC(p2);
  451         kg2 = FIRST_KSEGRP_IN_PROC(p2);
  452 
  453         /* Allocate and switch to an alternate kstack if specified. */
  454         if (pages != 0)
  455                 vm_thread_new_altkstack(td2, pages);
  456 
  457         PROC_LOCK(p2);
  458         PROC_LOCK(p1);
  459 
  460         bzero(&p2->p_startzero,
  461             __rangeof(struct proc, p_startzero, p_endzero));
  462         bzero(&td2->td_startzero,
  463             __rangeof(struct thread, td_startzero, td_endzero));
  464         bzero(&kg2->kg_startzero,
  465             __rangeof(struct ksegrp, kg_startzero, kg_endzero));
  466 
  467         bcopy(&p1->p_startcopy, &p2->p_startcopy,
  468             __rangeof(struct proc, p_startcopy, p_endcopy));
  469         bcopy(&td->td_startcopy, &td2->td_startcopy,
  470             __rangeof(struct thread, td_startcopy, td_endcopy));
  471         bcopy(&td->td_ksegrp->kg_startcopy, &kg2->kg_startcopy,
  472             __rangeof(struct ksegrp, kg_startcopy, kg_endcopy));
  473 
  474         td2->td_sigstk = td->td_sigstk;
  475         td2->td_sigmask = td->td_sigmask;
  476 
  477         /*
  478          * Duplicate sub-structures as needed.
  479          * Increase reference counts on shared objects.
  480          */
  481         p2->p_flag = 0;
  482         if (p1->p_flag & P_PROFIL)
  483                 startprofclock(p2);
  484         mtx_lock_spin(&sched_lock);
  485         p2->p_sflag = PS_INMEM;
  486         /*
  487          * Allow the scheduler to adjust the priority of the child and
  488          * parent while we hold the sched_lock.
  489          */
  490         sched_fork(td, td2);
  491 
  492         mtx_unlock_spin(&sched_lock);
  493         p2->p_ucred = crhold(td->td_ucred);
  494         td2->td_ucred = crhold(p2->p_ucred);    /* XXXKSE */
  495 
  496         pargs_hold(p2->p_args);
  497 
  498         if (flags & RFSIGSHARE) {
  499                 p2->p_sigacts = sigacts_hold(p1->p_sigacts);
  500         } else {
  501                 sigacts_copy(newsigacts, p1->p_sigacts);
  502                 p2->p_sigacts = newsigacts;
  503         }
  504         if (flags & RFLINUXTHPN) 
  505                 p2->p_sigparent = SIGUSR1;
  506         else
  507                 p2->p_sigparent = SIGCHLD;
  508 
  509         p2->p_textvp = p1->p_textvp;
  510         p2->p_fd = fd;
  511         p2->p_fdtol = fdtol;
  512 
  513         /*
  514          * p_limit is copy-on-write.  Bump its refcount.
  515          */
  516         p2->p_limit = lim_hold(p1->p_limit);
  517 
  518         pstats_fork(p1->p_stats, p2->p_stats);
  519 
  520         PROC_UNLOCK(p1);
  521         PROC_UNLOCK(p2);
  522 
  523         /* Bump references to the text vnode (for procfs) */
  524         if (p2->p_textvp)
  525                 vref(p2->p_textvp);
  526 
  527         /*
  528          * Set up linkage for kernel based threading.
  529          */
  530         if ((flags & RFTHREAD) != 0) {
  531                 mtx_lock(&ppeers_lock);
  532                 p2->p_peers = p1->p_peers;
  533                 p1->p_peers = p2;
  534                 p2->p_leader = p1->p_leader;
  535                 mtx_unlock(&ppeers_lock);
  536                 PROC_LOCK(p1->p_leader);
  537                 if ((p1->p_leader->p_flag & P_WEXIT) != 0) {
  538                         PROC_UNLOCK(p1->p_leader);
  539                         /*
  540                          * The task leader is exiting, so process p1 is
  541                          * going to be killed shortly.  Since p1 obviously
  542                          * isn't dead yet, we know that the leader is either
  543                          * sending SIGKILL's to all the processes in this
  544                          * task or is sleeping waiting for all the peers to
  545                          * exit.  We let p1 complete the fork, but we need
  546                          * to go ahead and kill the new process p2 since
  547                          * the task leader may not get a chance to send
  548                          * SIGKILL to it.  We leave it on the list so that
  549                          * the task leader will wait for this new process
  550                          * to commit suicide.
  551                          */
  552                         PROC_LOCK(p2);
  553                         psignal(p2, SIGKILL);
  554                         PROC_UNLOCK(p2);
  555                 } else
  556                         PROC_UNLOCK(p1->p_leader);
  557         } else {
  558                 p2->p_peers = NULL;
  559                 p2->p_leader = p2;
  560         }
  561 
  562         sx_xlock(&proctree_lock);
  563         PGRP_LOCK(p1->p_pgrp);
  564         PROC_LOCK(p2);
  565         PROC_LOCK(p1);
  566 
  567         /*
  568          * Preserve some more flags in subprocess.  P_PROFIL has already
  569          * been preserved.
  570          */
  571         p2->p_flag |= p1->p_flag & P_SUGID;
  572         td2->td_pflags |= td->td_pflags & TDP_ALTSTACK;
  573         SESS_LOCK(p1->p_session);
  574         if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
  575                 p2->p_flag |= P_CONTROLT;
  576         SESS_UNLOCK(p1->p_session);
  577         if (flags & RFPPWAIT)
  578                 p2->p_flag |= P_PPWAIT;
  579 
  580         p2->p_pgrp = p1->p_pgrp;
  581         LIST_INSERT_AFTER(p1, p2, p_pglist);
  582         PGRP_UNLOCK(p1->p_pgrp);
  583         LIST_INIT(&p2->p_children);
  584 
  585         callout_init(&p2->p_itcallout, CALLOUT_MPSAFE);
  586 
  587 #ifdef KTRACE
  588         /*
  589          * Copy traceflag and tracefile if enabled.
  590          */
  591         mtx_lock(&ktrace_mtx);
  592         KASSERT(p2->p_tracevp == NULL, ("new process has a ktrace vnode"));
  593         if (p1->p_traceflag & KTRFAC_INHERIT) {
  594                 p2->p_traceflag = p1->p_traceflag;
  595                 if ((p2->p_tracevp = p1->p_tracevp) != NULL) {
  596                         VREF(p2->p_tracevp);
  597                         KASSERT(p1->p_tracecred != NULL,
  598                             ("ktrace vnode with no cred"));
  599                         p2->p_tracecred = crhold(p1->p_tracecred);
  600                 }
  601         }
  602         mtx_unlock(&ktrace_mtx);
  603 #endif
  604 
  605         /*
  606          * If PF_FORK is set, the child process inherits the
  607          * procfs ioctl flags from its parent.
  608          */
  609         if (p1->p_pfsflags & PF_FORK) {
  610                 p2->p_stops = p1->p_stops;
  611                 p2->p_pfsflags = p1->p_pfsflags;
  612         }
  613 
  614         /*
  615          * This begins the section where we must prevent the parent
  616          * from being swapped.
  617          */
  618         _PHOLD(p1);
  619         PROC_UNLOCK(p1);
  620 
  621         /*
  622          * Attach the new process to its parent.
  623          *
  624          * If RFNOWAIT is set, the newly created process becomes a child
  625          * of init.  This effectively disassociates the child from the
  626          * parent.
  627          */
  628         if (flags & RFNOWAIT)
  629                 pptr = initproc;
  630         else
  631                 pptr = p1;
  632         p2->p_pptr = pptr;
  633         LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
  634         sx_xunlock(&proctree_lock);
  635 
  636         /* Inform accounting that we have forked. */
  637         p2->p_acflag = AFORK;
  638         PROC_UNLOCK(p2);
  639 
  640         /*
  641          * Finish creating the child process.  It will return via a different
  642          * execution path later.  (ie: directly into user mode)
  643          */
  644         vm_forkproc(td, p2, td2, flags);
  645 
  646         if (flags == (RFFDG | RFPROC)) {
  647                 atomic_add_int(&cnt.v_forks, 1);
  648                 atomic_add_int(&cnt.v_forkpages, p2->p_vmspace->vm_dsize +
  649                     p2->p_vmspace->vm_ssize);
  650         } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
  651                 atomic_add_int(&cnt.v_vforks, 1);
  652                 atomic_add_int(&cnt.v_vforkpages, p2->p_vmspace->vm_dsize +
  653                     p2->p_vmspace->vm_ssize);
  654         } else if (p1 == &proc0) {
  655                 atomic_add_int(&cnt.v_kthreads, 1);
  656                 atomic_add_int(&cnt.v_kthreadpages, p2->p_vmspace->vm_dsize +
  657                     p2->p_vmspace->vm_ssize);
  658         } else {
  659                 atomic_add_int(&cnt.v_rforks, 1);
  660                 atomic_add_int(&cnt.v_rforkpages, p2->p_vmspace->vm_dsize +
  661                     p2->p_vmspace->vm_ssize);
  662         }
  663 
  664         /*
  665          * Both processes are set up, now check if any loadable modules want
  666          * to adjust anything.
  667          *   What if they have an error? XXX
  668          */
  669         EVENTHANDLER_INVOKE(process_fork, p1, p2, flags);
  670 
  671         /*
  672          * Set the child start time and mark the process as being complete.
  673          */
  674         microuptime(&p2->p_stats->p_start);
  675         mtx_lock_spin(&sched_lock);
  676         p2->p_state = PRS_NORMAL;
  677 
  678         /*
  679          * If RFSTOPPED not requested, make child runnable and add to
  680          * run queue.
  681          */
  682         if ((flags & RFSTOPPED) == 0) {
  683                 TD_SET_CAN_RUN(td2);
  684                 setrunqueue(td2, SRQ_BORING);
  685         }
  686         mtx_unlock_spin(&sched_lock);
  687 
  688         /*
  689          * Now can be swapped.
  690          */
  691         PROC_LOCK(p1);
  692         _PRELE(p1);
  693 
  694         /*
  695          * Tell any interested parties about the new process.
  696          */
  697         KNOTE_LOCKED(&p1->p_klist, NOTE_FORK | p2->p_pid);
  698 
  699         PROC_UNLOCK(p1);
  700 
  701         /*
  702          * Preserve synchronization semantics of vfork.  If waiting for
  703          * child to exec or exit, set P_PPWAIT on child, and sleep on our
  704          * proc (in case of exit).
  705          */
  706         PROC_LOCK(p2);
  707         while (p2->p_flag & P_PPWAIT)
  708                 msleep(p1, &p2->p_mtx, PWAIT, "ppwait", 0);
  709         PROC_UNLOCK(p2);
  710 
  711         /*
  712          * If other threads are waiting, let them continue now.
  713          */
  714         if (p1->p_flag & P_HADTHREADS) {
  715                 PROC_LOCK(p1);
  716                 thread_single_end();
  717                 PROC_UNLOCK(p1);
  718         }
  719 
  720         /*
  721          * Return child proc pointer to parent.
  722          */
  723         *procp = p2;
  724         return (0);
  725 fail:
  726         sx_sunlock(&proctree_lock);
  727         if (ppsratecheck(&lastfail, &curfail, 1))
  728                 printf("maxproc limit exceeded by uid %i, please see tuning(7) and login.conf(5).\n",
  729                         uid);
  730         sx_xunlock(&allproc_lock);
  731 #ifdef MAC
  732         mac_destroy_proc(newproc);
  733 #endif
  734         uma_zfree(proc_zone, newproc);
  735         if (p1->p_flag & P_HADTHREADS) {
  736                 PROC_LOCK(p1);
  737                 thread_single_end();
  738                 PROC_UNLOCK(p1);
  739         }
  740         tsleep(&forksleep, PUSER, "fork", hz / 2);
  741         return (error);
  742 }
  743 
  744 /*
  745  * Handle the return of a child process from fork1().  This function
  746  * is called from the MD fork_trampoline() entry point.
  747  */
  748 void
  749 fork_exit(callout, arg, frame)
  750         void (*callout)(void *, struct trapframe *);
  751         void *arg;
  752         struct trapframe *frame;
  753 {
  754         struct proc *p;
  755         struct thread *td;
  756 
  757         /*
  758          * Finish setting up thread glue so that it begins execution in a
  759          * non-nested critical section with sched_lock held but not recursed.
  760          */
  761         td = curthread;
  762         p = td->td_proc;
  763         td->td_oncpu = PCPU_GET(cpuid);
  764         KASSERT(p->p_state == PRS_NORMAL, ("executing process is still new"));
  765 
  766         sched_lock.mtx_lock = (uintptr_t)td;
  767         mtx_assert(&sched_lock, MA_OWNED | MA_NOTRECURSED);
  768         cpu_critical_fork_exit();
  769         CTR4(KTR_PROC, "fork_exit: new thread %p (kse %p, pid %d, %s)",
  770                 td, td->td_sched, p->p_pid, p->p_comm);
  771 
  772         /*
  773          * Processes normally resume in mi_switch() after being
  774          * cpu_switch()'ed to, but when children start up they arrive here
  775          * instead, so we must do much the same things as mi_switch() would.
  776          */
  777 
  778         if ((td = PCPU_GET(deadthread))) {
  779                 PCPU_SET(deadthread, NULL);
  780                 thread_stash(td);
  781         }
  782         td = curthread;
  783         mtx_unlock_spin(&sched_lock);
  784 
  785         /*
  786          * cpu_set_fork_handler intercepts this function call to
  787          * have this call a non-return function to stay in kernel mode.
  788          * initproc has its own fork handler, but it does return.
  789          */
  790         KASSERT(callout != NULL, ("NULL callout in fork_exit"));
  791         callout(arg, frame);
  792 
  793         /*
  794          * Check if a kernel thread misbehaved and returned from its main
  795          * function.
  796          */
  797         PROC_LOCK(p);
  798         if (p->p_flag & P_KTHREAD) {
  799                 PROC_UNLOCK(p);
  800                 printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
  801                     p->p_comm, p->p_pid);
  802                 kthread_exit(0);
  803         }
  804         PROC_UNLOCK(p);
  805         mtx_assert(&Giant, MA_NOTOWNED);
  806 }
  807 
  808 /*
  809  * Simplified back end of syscall(), used when returning from fork()
  810  * directly into user mode.  Giant is not held on entry, and must not
  811  * be held on return.  This function is passed in to fork_exit() as the
  812  * first parameter and is called when returning to a new userland process.
  813  */
  814 void
  815 fork_return(td, frame)
  816         struct thread *td;
  817         struct trapframe *frame;
  818 {
  819 
  820         userret(td, frame, 0);
  821 #ifdef KTRACE
  822         if (KTRPOINT(td, KTR_SYSRET))
  823                 ktrsysret(SYS_fork, 0, 0);
  824 #endif
  825         mtx_assert(&Giant, MA_NOTOWNED);
  826 }

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