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/6.0/sys/kern/kern_fork.c 147730 2005-07-01 16:28:32Z ssouhlal $");
   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 
   76 #ifndef _SYS_SYSPROTO_H_
   77 struct fork_args {
   78         int     dummy;
   79 };
   80 #endif
   81 
   82 static int forksleep; /* Place for fork1() to sleep on. */
   83 
   84 /*
   85  * MPSAFE
   86  */
   87 /* ARGSUSED */
   88 int
   89 fork(td, uap)
   90         struct thread *td;
   91         struct fork_args *uap;
   92 {
   93         int error;
   94         struct proc *p2;
   95 
   96         error = fork1(td, RFFDG | RFPROC, 0, &p2);
   97         if (error == 0) {
   98                 td->td_retval[0] = p2->p_pid;
   99                 td->td_retval[1] = 0;
  100         }
  101         return (error);
  102 }
  103 
  104 /*
  105  * MPSAFE
  106  */
  107 /* ARGSUSED */
  108 int
  109 vfork(td, uap)
  110         struct thread *td;
  111         struct vfork_args *uap;
  112 {
  113         int error;
  114         struct proc *p2;
  115 
  116         error = fork1(td, RFFDG | RFPROC | RFPPWAIT | RFMEM, 0, &p2);
  117         if (error == 0) {
  118                 td->td_retval[0] = p2->p_pid;
  119                 td->td_retval[1] = 0;
  120         }
  121         return (error);
  122 }
  123 
  124 /*
  125  * MPSAFE
  126  */
  127 int
  128 rfork(td, uap)
  129         struct thread *td;
  130         struct rfork_args *uap;
  131 {
  132         struct proc *p2;
  133         int error;
  134 
  135         /* Don't allow kernel-only flags. */
  136         if ((uap->flags & RFKERNELONLY) != 0)
  137                 return (EINVAL);
  138 
  139         error = fork1(td, uap->flags, 0, &p2);
  140         if (error == 0) {
  141                 td->td_retval[0] = p2 ? p2->p_pid : 0;
  142                 td->td_retval[1] = 0;
  143         }
  144         return (error);
  145 }
  146 
  147 int     nprocs = 1;             /* process 0 */
  148 int     lastpid = 0;
  149 SYSCTL_INT(_kern, OID_AUTO, lastpid, CTLFLAG_RD, &lastpid, 0, 
  150     "Last used PID");
  151 
  152 /*
  153  * Random component to lastpid generation.  We mix in a random factor to make
  154  * it a little harder to predict.  We sanity check the modulus value to avoid
  155  * doing it in critical paths.  Don't let it be too small or we pointlessly
  156  * waste randomness entropy, and don't let it be impossibly large.  Using a
  157  * modulus that is too big causes a LOT more process table scans and slows
  158  * down fork processing as the pidchecked caching is defeated.
  159  */
  160 static int randompid = 0;
  161 
  162 static int
  163 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
  164 {
  165         int error, pid;
  166 
  167         error = sysctl_wire_old_buffer(req, sizeof(int));
  168         if (error != 0)
  169                 return(error);
  170         sx_xlock(&allproc_lock);
  171         pid = randompid;
  172         error = sysctl_handle_int(oidp, &pid, 0, req);
  173         if (error == 0 && req->newptr != NULL) {
  174                 if (pid < 0 || pid > PID_MAX - 100)     /* out of range */
  175                         pid = PID_MAX - 100;
  176                 else if (pid < 2)                       /* NOP */
  177                         pid = 0;
  178                 else if (pid < 100)                     /* Make it reasonable */
  179                         pid = 100;
  180                 randompid = pid;
  181         }
  182         sx_xunlock(&allproc_lock);
  183         return (error);
  184 }
  185 
  186 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
  187     0, 0, sysctl_kern_randompid, "I", "Random PID modulus");
  188 
  189 int
  190 fork1(td, flags, pages, procp)
  191         struct thread *td;
  192         int flags;
  193         int pages;
  194         struct proc **procp;
  195 {
  196         struct proc *p1, *p2, *pptr;
  197         uid_t uid;
  198         struct proc *newproc;
  199         int ok, trypid;
  200         static int curfail, pidchecked = 0;
  201         static struct timeval lastfail;
  202         struct filedesc *fd;
  203         struct filedesc_to_leader *fdtol;
  204         struct thread *td2;
  205         struct ksegrp *kg2;
  206         struct sigacts *newsigacts;
  207         int error;
  208 
  209         /* Can't copy and clear. */
  210         if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
  211                 return (EINVAL);
  212 
  213         p1 = td->td_proc;
  214 
  215         /*
  216          * Here we don't create a new process, but we divorce
  217          * certain parts of a process from itself.
  218          */
  219         if ((flags & RFPROC) == 0) {
  220                 vm_forkproc(td, NULL, NULL, flags);
  221 
  222                 /*
  223                  * Close all file descriptors.
  224                  */
  225                 if (flags & RFCFDG) {
  226                         struct filedesc *fdtmp;
  227                         fdtmp = fdinit(td->td_proc->p_fd);
  228                         fdfree(td);
  229                         p1->p_fd = fdtmp;
  230                 }
  231 
  232                 /*
  233                  * Unshare file descriptors (from parent).
  234                  */
  235                 if (flags & RFFDG) 
  236                         fdunshare(p1, td);
  237                 *procp = NULL;
  238                 return (0);
  239         }
  240 
  241         /*
  242          * Note 1:1 allows for forking with one thread coming out on the
  243          * other side with the expectation that the process is about to
  244          * exec.
  245          */
  246         if (p1->p_flag & P_HADTHREADS) {
  247                 /*
  248                  * Idle the other threads for a second.
  249                  * Since the user space is copied, it must remain stable.
  250                  * In addition, all threads (from the user perspective)
  251                  * need to either be suspended or in the kernel,
  252                  * where they will try restart in the parent and will
  253                  * be aborted in the child.
  254                  */
  255                 PROC_LOCK(p1);
  256                 if (thread_single(SINGLE_NO_EXIT)) {
  257                         /* Abort. Someone else is single threading before us. */
  258                         PROC_UNLOCK(p1);
  259                         return (ERESTART);
  260                 }
  261                 PROC_UNLOCK(p1);
  262                 /*
  263                  * All other activity in this process
  264                  * is now suspended at the user boundary,
  265                  * (or other safe places if we think of any).
  266                  */
  267         }
  268 
  269         /* Allocate new proc. */
  270         newproc = uma_zalloc(proc_zone, M_WAITOK);
  271 #ifdef MAC
  272         mac_init_proc(newproc);
  273 #endif
  274         knlist_init(&newproc->p_klist, &newproc->p_mtx, NULL, NULL, NULL);
  275 
  276         /* We have to lock the process tree while we look for a pid. */
  277         sx_slock(&proctree_lock);
  278 
  279         /*
  280          * Although process entries are dynamically created, we still keep
  281          * a global limit on the maximum number we will create.  Don't allow
  282          * a nonprivileged user to use the last ten processes; don't let root
  283          * exceed the limit. The variable nprocs is the current number of
  284          * processes, maxproc is the limit.
  285          */
  286         sx_xlock(&allproc_lock);
  287         uid = td->td_ucred->cr_ruid;
  288         if ((nprocs >= maxproc - 10 &&
  289             suser_cred(td->td_ucred, SUSER_RUID) != 0) ||
  290             nprocs >= maxproc) {
  291                 error = EAGAIN;
  292                 goto fail;
  293         }
  294 
  295         /*
  296          * Increment the count of procs running with this uid. Don't allow
  297          * a nonprivileged user to exceed their current limit.
  298          */
  299         PROC_LOCK(p1);
  300         ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1,
  301                 (uid != 0) ? lim_cur(p1, RLIMIT_NPROC) : 0);
  302         PROC_UNLOCK(p1);
  303         if (!ok) {
  304                 error = EAGAIN;
  305                 goto fail;
  306         }
  307 
  308         /*
  309          * Increment the nprocs resource before blocking can occur.  There
  310          * are hard-limits as to the number of processes that can run.
  311          */
  312         nprocs++;
  313 
  314         /*
  315          * Find an unused process ID.  We remember a range of unused IDs
  316          * ready to use (from lastpid+1 through pidchecked-1).
  317          *
  318          * If RFHIGHPID is set (used during system boot), do not allocate
  319          * low-numbered pids.
  320          */
  321         trypid = lastpid + 1;
  322         if (flags & RFHIGHPID) {
  323                 if (trypid < 10)
  324                         trypid = 10;
  325         } else {
  326                 if (randompid)
  327                         trypid += arc4random() % randompid;
  328         }
  329 retry:
  330         /*
  331          * If the process ID prototype has wrapped around,
  332          * restart somewhat above 0, as the low-numbered procs
  333          * tend to include daemons that don't exit.
  334          */
  335         if (trypid >= PID_MAX) {
  336                 trypid = trypid % PID_MAX;
  337                 if (trypid < 100)
  338                         trypid += 100;
  339                 pidchecked = 0;
  340         }
  341         if (trypid >= pidchecked) {
  342                 int doingzomb = 0;
  343 
  344                 pidchecked = PID_MAX;
  345                 /*
  346                  * Scan the active and zombie procs to check whether this pid
  347                  * is in use.  Remember the lowest pid that's greater
  348                  * than trypid, so we can avoid checking for a while.
  349                  */
  350                 p2 = LIST_FIRST(&allproc);
  351 again:
  352                 for (; p2 != NULL; p2 = LIST_NEXT(p2, p_list)) {
  353                         PROC_LOCK(p2);
  354                         while (p2->p_pid == trypid ||
  355                             (p2->p_pgrp != NULL &&
  356                             (p2->p_pgrp->pg_id == trypid ||
  357                             (p2->p_session != NULL &&
  358                             p2->p_session->s_sid == trypid)))) {
  359                                 trypid++;
  360                                 if (trypid >= pidchecked) {
  361                                         PROC_UNLOCK(p2);
  362                                         goto retry;
  363                                 }
  364                         }
  365                         if (p2->p_pid > trypid && pidchecked > p2->p_pid)
  366                                 pidchecked = p2->p_pid;
  367                         if (p2->p_pgrp != NULL) {
  368                                 if (p2->p_pgrp->pg_id > trypid &&
  369                                     pidchecked > p2->p_pgrp->pg_id)
  370                                         pidchecked = p2->p_pgrp->pg_id;
  371                                 if (p2->p_session != NULL &&
  372                                     p2->p_session->s_sid > trypid &&
  373                                     pidchecked > p2->p_session->s_sid)
  374                                         pidchecked = p2->p_session->s_sid;
  375                         }
  376                         PROC_UNLOCK(p2);
  377                 }
  378                 if (!doingzomb) {
  379                         doingzomb = 1;
  380                         p2 = LIST_FIRST(&zombproc);
  381                         goto again;
  382                 }
  383         }
  384         sx_sunlock(&proctree_lock);
  385 
  386         /*
  387          * RFHIGHPID does not mess with the lastpid counter during boot.
  388          */
  389         if (flags & RFHIGHPID)
  390                 pidchecked = 0;
  391         else
  392                 lastpid = trypid;
  393 
  394         p2 = newproc;
  395         p2->p_state = PRS_NEW;          /* protect against others */
  396         p2->p_pid = trypid;
  397         LIST_INSERT_HEAD(&allproc, p2, p_list);
  398         LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
  399         sx_xunlock(&allproc_lock);
  400 
  401         /*
  402          * Malloc things while we don't hold any locks.
  403          */
  404         if (flags & RFSIGSHARE)
  405                 newsigacts = NULL;
  406         else
  407                 newsigacts = sigacts_alloc();
  408 
  409         /*
  410          * Copy filedesc.
  411          */
  412         if (flags & RFCFDG) {
  413                 fd = fdinit(p1->p_fd);
  414                 fdtol = NULL;
  415         } else if (flags & RFFDG) {
  416                 fd = fdcopy(p1->p_fd);
  417                 fdtol = NULL;
  418         } else {
  419                 fd = fdshare(p1->p_fd);
  420                 if (p1->p_fdtol == NULL)
  421                         p1->p_fdtol =
  422                                 filedesc_to_leader_alloc(NULL,
  423                                                          NULL,
  424                                                          p1->p_leader);
  425                 if ((flags & RFTHREAD) != 0) {
  426                         /*
  427                          * Shared file descriptor table and
  428                          * shared process leaders.
  429                          */
  430                         fdtol = p1->p_fdtol;
  431                         FILEDESC_LOCK_FAST(p1->p_fd);
  432                         fdtol->fdl_refcount++;
  433                         FILEDESC_UNLOCK_FAST(p1->p_fd);
  434                 } else {
  435                         /* 
  436                          * Shared file descriptor table, and
  437                          * different process leaders 
  438                          */
  439                         fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
  440                                                          p1->p_fd,
  441                                                          p2);
  442                 }
  443         }
  444         /*
  445          * Make a proc table entry for the new process.
  446          * Start by zeroing the section of proc that is zero-initialized,
  447          * then copy the section that is copied directly from the parent.
  448          */
  449         td2 = FIRST_THREAD_IN_PROC(p2);
  450         kg2 = FIRST_KSEGRP_IN_PROC(p2);
  451 
  452         /* Allocate and switch to an alternate kstack if specified. */
  453         if (pages != 0)
  454                 vm_thread_new_altkstack(td2, pages);
  455 
  456         PROC_LOCK(p2);
  457         PROC_LOCK(p1);
  458 
  459         bzero(&p2->p_startzero,
  460             __rangeof(struct proc, p_startzero, p_endzero));
  461         bzero(&td2->td_startzero,
  462             __rangeof(struct thread, td_startzero, td_endzero));
  463         bzero(&kg2->kg_startzero,
  464             __rangeof(struct ksegrp, kg_startzero, kg_endzero));
  465 
  466         bcopy(&p1->p_startcopy, &p2->p_startcopy,
  467             __rangeof(struct proc, p_startcopy, p_endcopy));
  468         bcopy(&td->td_startcopy, &td2->td_startcopy,
  469             __rangeof(struct thread, td_startcopy, td_endcopy));
  470         bcopy(&td->td_ksegrp->kg_startcopy, &kg2->kg_startcopy,
  471             __rangeof(struct ksegrp, kg_startcopy, kg_endcopy));
  472 
  473         td2->td_sigstk = td->td_sigstk;
  474         td2->td_sigmask = td->td_sigmask;
  475 
  476         /*
  477          * Duplicate sub-structures as needed.
  478          * Increase reference counts on shared objects.
  479          */
  480         p2->p_flag = 0;
  481         if (p1->p_flag & P_PROFIL)
  482                 startprofclock(p2);
  483         mtx_lock_spin(&sched_lock);
  484         p2->p_sflag = PS_INMEM;
  485         /*
  486          * Allow the scheduler to adjust the priority of the child and
  487          * parent while we hold the sched_lock.
  488          */
  489         sched_fork(td, td2);
  490 
  491         mtx_unlock_spin(&sched_lock);
  492         p2->p_ucred = crhold(td->td_ucred);
  493         td2->td_ucred = crhold(p2->p_ucred);    /* XXXKSE */
  494 
  495         pargs_hold(p2->p_args);
  496 
  497         if (flags & RFSIGSHARE) {
  498                 p2->p_sigacts = sigacts_hold(p1->p_sigacts);
  499         } else {
  500                 sigacts_copy(newsigacts, p1->p_sigacts);
  501                 p2->p_sigacts = newsigacts;
  502         }
  503         if (flags & RFLINUXTHPN) 
  504                 p2->p_sigparent = SIGUSR1;
  505         else
  506                 p2->p_sigparent = SIGCHLD;
  507 
  508         p2->p_textvp = p1->p_textvp;
  509         p2->p_fd = fd;
  510         p2->p_fdtol = fdtol;
  511 
  512         /*
  513          * p_limit is copy-on-write.  Bump its refcount.
  514          */
  515         p2->p_limit = lim_hold(p1->p_limit);
  516 
  517         pstats_fork(p1->p_stats, p2->p_stats);
  518 
  519         PROC_UNLOCK(p1);
  520         PROC_UNLOCK(p2);
  521 
  522         /* Bump references to the text vnode (for procfs) */
  523         if (p2->p_textvp)
  524                 vref(p2->p_textvp);
  525 
  526         /*
  527          * Set up linkage for kernel based threading.
  528          */
  529         if ((flags & RFTHREAD) != 0) {
  530                 mtx_lock(&ppeers_lock);
  531                 p2->p_peers = p1->p_peers;
  532                 p1->p_peers = p2;
  533                 p2->p_leader = p1->p_leader;
  534                 mtx_unlock(&ppeers_lock);
  535                 PROC_LOCK(p1->p_leader);
  536                 if ((p1->p_leader->p_flag & P_WEXIT) != 0) {
  537                         PROC_UNLOCK(p1->p_leader);
  538                         /*
  539                          * The task leader is exiting, so process p1 is
  540                          * going to be killed shortly.  Since p1 obviously
  541                          * isn't dead yet, we know that the leader is either
  542                          * sending SIGKILL's to all the processes in this
  543                          * task or is sleeping waiting for all the peers to
  544                          * exit.  We let p1 complete the fork, but we need
  545                          * to go ahead and kill the new process p2 since
  546                          * the task leader may not get a chance to send
  547                          * SIGKILL to it.  We leave it on the list so that
  548                          * the task leader will wait for this new process
  549                          * to commit suicide.
  550                          */
  551                         PROC_LOCK(p2);
  552                         psignal(p2, SIGKILL);
  553                         PROC_UNLOCK(p2);
  554                 } else
  555                         PROC_UNLOCK(p1->p_leader);
  556         } else {
  557                 p2->p_peers = NULL;
  558                 p2->p_leader = p2;
  559         }
  560 
  561         sx_xlock(&proctree_lock);
  562         PGRP_LOCK(p1->p_pgrp);
  563         PROC_LOCK(p2);
  564         PROC_LOCK(p1);
  565 
  566         /*
  567          * Preserve some more flags in subprocess.  P_PROFIL has already
  568          * been preserved.
  569          */
  570         p2->p_flag |= p1->p_flag & P_SUGID;
  571         td2->td_pflags |= td->td_pflags & TDP_ALTSTACK;
  572         SESS_LOCK(p1->p_session);
  573         if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
  574                 p2->p_flag |= P_CONTROLT;
  575         SESS_UNLOCK(p1->p_session);
  576         if (flags & RFPPWAIT)
  577                 p2->p_flag |= P_PPWAIT;
  578 
  579         p2->p_pgrp = p1->p_pgrp;
  580         LIST_INSERT_AFTER(p1, p2, p_pglist);
  581         PGRP_UNLOCK(p1->p_pgrp);
  582         LIST_INIT(&p2->p_children);
  583 
  584         callout_init(&p2->p_itcallout, CALLOUT_MPSAFE);
  585 
  586 #ifdef KTRACE
  587         /*
  588          * Copy traceflag and tracefile if enabled.
  589          */
  590         mtx_lock(&ktrace_mtx);
  591         KASSERT(p2->p_tracevp == NULL, ("new process has a ktrace vnode"));
  592         if (p1->p_traceflag & KTRFAC_INHERIT) {
  593                 p2->p_traceflag = p1->p_traceflag;
  594                 if ((p2->p_tracevp = p1->p_tracevp) != NULL) {
  595                         VREF(p2->p_tracevp);
  596                         KASSERT(p1->p_tracecred != NULL,
  597                             ("ktrace vnode with no cred"));
  598                         p2->p_tracecred = crhold(p1->p_tracecred);
  599                 }
  600         }
  601         mtx_unlock(&ktrace_mtx);
  602 #endif
  603 
  604         /*
  605          * If PF_FORK is set, the child process inherits the
  606          * procfs ioctl flags from its parent.
  607          */
  608         if (p1->p_pfsflags & PF_FORK) {
  609                 p2->p_stops = p1->p_stops;
  610                 p2->p_pfsflags = p1->p_pfsflags;
  611         }
  612 
  613         /*
  614          * This begins the section where we must prevent the parent
  615          * from being swapped.
  616          */
  617         _PHOLD(p1);
  618         PROC_UNLOCK(p1);
  619 
  620         /*
  621          * Attach the new process to its parent.
  622          *
  623          * If RFNOWAIT is set, the newly created process becomes a child
  624          * of init.  This effectively disassociates the child from the
  625          * parent.
  626          */
  627         if (flags & RFNOWAIT)
  628                 pptr = initproc;
  629         else
  630                 pptr = p1;
  631         p2->p_pptr = pptr;
  632         LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
  633         sx_xunlock(&proctree_lock);
  634 
  635         /* Inform accounting that we have forked. */
  636         p2->p_acflag = AFORK;
  637         PROC_UNLOCK(p2);
  638 
  639         /*
  640          * Finish creating the child process.  It will return via a different
  641          * execution path later.  (ie: directly into user mode)
  642          */
  643         vm_forkproc(td, p2, td2, flags);
  644 
  645         if (flags == (RFFDG | RFPROC)) {
  646                 atomic_add_int(&cnt.v_forks, 1);
  647                 atomic_add_int(&cnt.v_forkpages, p2->p_vmspace->vm_dsize +
  648                     p2->p_vmspace->vm_ssize);
  649         } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
  650                 atomic_add_int(&cnt.v_vforks, 1);
  651                 atomic_add_int(&cnt.v_vforkpages, p2->p_vmspace->vm_dsize +
  652                     p2->p_vmspace->vm_ssize);
  653         } else if (p1 == &proc0) {
  654                 atomic_add_int(&cnt.v_kthreads, 1);
  655                 atomic_add_int(&cnt.v_kthreadpages, p2->p_vmspace->vm_dsize +
  656                     p2->p_vmspace->vm_ssize);
  657         } else {
  658                 atomic_add_int(&cnt.v_rforks, 1);
  659                 atomic_add_int(&cnt.v_rforkpages, p2->p_vmspace->vm_dsize +
  660                     p2->p_vmspace->vm_ssize);
  661         }
  662 
  663         /*
  664          * Both processes are set up, now check if any loadable modules want
  665          * to adjust anything.
  666          *   What if they have an error? XXX
  667          */
  668         EVENTHANDLER_INVOKE(process_fork, p1, p2, flags);
  669 
  670         /*
  671          * Set the child start time and mark the process as being complete.
  672          */
  673         microuptime(&p2->p_stats->p_start);
  674         mtx_lock_spin(&sched_lock);
  675         p2->p_state = PRS_NORMAL;
  676 
  677         /*
  678          * If RFSTOPPED not requested, make child runnable and add to
  679          * run queue.
  680          */
  681         if ((flags & RFSTOPPED) == 0) {
  682                 TD_SET_CAN_RUN(td2);
  683                 setrunqueue(td2, SRQ_BORING);
  684         }
  685         mtx_unlock_spin(&sched_lock);
  686 
  687         /*
  688          * Now can be swapped.
  689          */
  690         PROC_LOCK(p1);
  691         _PRELE(p1);
  692 
  693         /*
  694          * Tell any interested parties about the new process.
  695          */
  696         KNOTE_LOCKED(&p1->p_klist, NOTE_FORK | p2->p_pid);
  697 
  698         PROC_UNLOCK(p1);
  699 
  700         /*
  701          * Preserve synchronization semantics of vfork.  If waiting for
  702          * child to exec or exit, set P_PPWAIT on child, and sleep on our
  703          * proc (in case of exit).
  704          */
  705         PROC_LOCK(p2);
  706         while (p2->p_flag & P_PPWAIT)
  707                 msleep(p1, &p2->p_mtx, PWAIT, "ppwait", 0);
  708         PROC_UNLOCK(p2);
  709 
  710         /*
  711          * If other threads are waiting, let them continue now.
  712          */
  713         if (p1->p_flag & P_HADTHREADS) {
  714                 PROC_LOCK(p1);
  715                 thread_single_end();
  716                 PROC_UNLOCK(p1);
  717         }
  718 
  719         /*
  720          * Return child proc pointer to parent.
  721          */
  722         *procp = p2;
  723         return (0);
  724 fail:
  725         sx_sunlock(&proctree_lock);
  726         if (ppsratecheck(&lastfail, &curfail, 1))
  727                 printf("maxproc limit exceeded by uid %i, please see tuning(7) and login.conf(5).\n",
  728                         uid);
  729         sx_xunlock(&allproc_lock);
  730 #ifdef MAC
  731         mac_destroy_proc(newproc);
  732 #endif
  733         uma_zfree(proc_zone, newproc);
  734         if (p1->p_flag & P_HADTHREADS) {
  735                 PROC_LOCK(p1);
  736                 thread_single_end();
  737                 PROC_UNLOCK(p1);
  738         }
  739         tsleep(&forksleep, PUSER, "fork", hz / 2);
  740         return (error);
  741 }
  742 
  743 /*
  744  * Handle the return of a child process from fork1().  This function
  745  * is called from the MD fork_trampoline() entry point.
  746  */
  747 void
  748 fork_exit(callout, arg, frame)
  749         void (*callout)(void *, struct trapframe *);
  750         void *arg;
  751         struct trapframe *frame;
  752 {
  753         struct proc *p;
  754         struct thread *td;
  755 
  756         /*
  757          * Finish setting up thread glue so that it begins execution in a
  758          * non-nested critical section with sched_lock held but not recursed.
  759          */
  760         td = curthread;
  761         p = td->td_proc;
  762         td->td_oncpu = PCPU_GET(cpuid);
  763         KASSERT(p->p_state == PRS_NORMAL, ("executing process is still new"));
  764 
  765         sched_lock.mtx_lock = (uintptr_t)td;
  766         mtx_assert(&sched_lock, MA_OWNED | MA_NOTRECURSED);
  767         CTR4(KTR_PROC, "fork_exit: new thread %p (kse %p, pid %d, %s)",
  768                 td, td->td_sched, p->p_pid, p->p_comm);
  769 
  770         /*
  771          * Processes normally resume in mi_switch() after being
  772          * cpu_switch()'ed to, but when children start up they arrive here
  773          * instead, so we must do much the same things as mi_switch() would.
  774          */
  775 
  776         if ((td = PCPU_GET(deadthread))) {
  777                 PCPU_SET(deadthread, NULL);
  778                 thread_stash(td);
  779         }
  780         td = curthread;
  781         mtx_unlock_spin(&sched_lock);
  782 
  783         /*
  784          * cpu_set_fork_handler intercepts this function call to
  785          * have this call a non-return function to stay in kernel mode.
  786          * initproc has its own fork handler, but it does return.
  787          */
  788         KASSERT(callout != NULL, ("NULL callout in fork_exit"));
  789         callout(arg, frame);
  790 
  791         /*
  792          * Check if a kernel thread misbehaved and returned from its main
  793          * function.
  794          */
  795         PROC_LOCK(p);
  796         if (p->p_flag & P_KTHREAD) {
  797                 PROC_UNLOCK(p);
  798                 printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
  799                     p->p_comm, p->p_pid);
  800                 kthread_exit(0);
  801         }
  802         PROC_UNLOCK(p);
  803         mtx_assert(&Giant, MA_NOTOWNED);
  804 }
  805 
  806 /*
  807  * Simplified back end of syscall(), used when returning from fork()
  808  * directly into user mode.  Giant is not held on entry, and must not
  809  * be held on return.  This function is passed in to fork_exit() as the
  810  * first parameter and is called when returning to a new userland process.
  811  */
  812 void
  813 fork_return(td, frame)
  814         struct thread *td;
  815         struct trapframe *frame;
  816 {
  817 
  818         userret(td, frame, 0);
  819 #ifdef KTRACE
  820         if (KTRPOINT(td, KTR_SYSRET))
  821                 ktrsysret(SYS_fork, 0, 0);
  822 #endif
  823         mtx_assert(&Giant, MA_NOTOWNED);
  824 }

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