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/8.1/sys/kern/kern_fork.c 207916 2010-05-11 13:18:41Z kib $");
   39 
   40 #include "opt_kdtrace.h"
   41 #include "opt_ktrace.h"
   42 #include "opt_kstack_pages.h"
   43 
   44 #include <sys/param.h>
   45 #include <sys/systm.h>
   46 #include <sys/sysproto.h>
   47 #include <sys/eventhandler.h>
   48 #include <sys/filedesc.h>
   49 #include <sys/jail.h>
   50 #include <sys/kernel.h>
   51 #include <sys/kthread.h>
   52 #include <sys/sysctl.h>
   53 #include <sys/lock.h>
   54 #include <sys/malloc.h>
   55 #include <sys/mutex.h>
   56 #include <sys/priv.h>
   57 #include <sys/proc.h>
   58 #include <sys/pioctl.h>
   59 #include <sys/resourcevar.h>
   60 #include <sys/sched.h>
   61 #include <sys/syscall.h>
   62 #include <sys/vmmeter.h>
   63 #include <sys/vnode.h>
   64 #include <sys/acct.h>
   65 #include <sys/ktr.h>
   66 #include <sys/ktrace.h>
   67 #include <sys/unistd.h> 
   68 #include <sys/sdt.h>
   69 #include <sys/sx.h>
   70 #include <sys/signalvar.h>
   71 
   72 #include <security/audit/audit.h>
   73 #include <security/mac/mac_framework.h>
   74 
   75 #include <vm/vm.h>
   76 #include <vm/pmap.h>
   77 #include <vm/vm_map.h>
   78 #include <vm/vm_extern.h>
   79 #include <vm/uma.h>
   80 
   81 #ifdef KDTRACE_HOOKS
   82 #include <sys/dtrace_bsd.h>
   83 dtrace_fork_func_t      dtrace_fasttrap_fork;
   84 #endif
   85 
   86 SDT_PROVIDER_DECLARE(proc);
   87 SDT_PROBE_DEFINE(proc, kernel, , create);
   88 SDT_PROBE_ARGTYPE(proc, kernel, , create, 0, "struct proc *");
   89 SDT_PROBE_ARGTYPE(proc, kernel, , create, 1, "struct proc *");
   90 SDT_PROBE_ARGTYPE(proc, kernel, , create, 2, "int");
   91 
   92 #ifndef _SYS_SYSPROTO_H_
   93 struct fork_args {
   94         int     dummy;
   95 };
   96 #endif
   97 
   98 /* ARGSUSED */
   99 int
  100 fork(td, uap)
  101         struct thread *td;
  102         struct fork_args *uap;
  103 {
  104         int error;
  105         struct proc *p2;
  106 
  107         error = fork1(td, RFFDG | RFPROC, 0, &p2);
  108         if (error == 0) {
  109                 td->td_retval[0] = p2->p_pid;
  110                 td->td_retval[1] = 0;
  111         }
  112         return (error);
  113 }
  114 
  115 /* ARGSUSED */
  116 int
  117 vfork(td, uap)
  118         struct thread *td;
  119         struct vfork_args *uap;
  120 {
  121         int error, flags;
  122         struct proc *p2;
  123 
  124 #ifdef XEN
  125         flags = RFFDG | RFPROC; /* validate that this is still an issue */
  126 #else
  127         flags = RFFDG | RFPROC | RFPPWAIT | RFMEM;
  128 #endif          
  129         error = fork1(td, flags, 0, &p2);
  130         if (error == 0) {
  131                 td->td_retval[0] = p2->p_pid;
  132                 td->td_retval[1] = 0;
  133         }
  134         return (error);
  135 }
  136 
  137 int
  138 rfork(td, uap)
  139         struct thread *td;
  140         struct rfork_args *uap;
  141 {
  142         struct proc *p2;
  143         int error;
  144 
  145         /* Don't allow kernel-only flags. */
  146         if ((uap->flags & RFKERNELONLY) != 0)
  147                 return (EINVAL);
  148 
  149         AUDIT_ARG_FFLAGS(uap->flags);
  150         error = fork1(td, uap->flags, 0, &p2);
  151         if (error == 0) {
  152                 td->td_retval[0] = p2 ? p2->p_pid : 0;
  153                 td->td_retval[1] = 0;
  154         }
  155         return (error);
  156 }
  157 
  158 int     nprocs = 1;             /* process 0 */
  159 int     lastpid = 0;
  160 SYSCTL_INT(_kern, OID_AUTO, lastpid, CTLFLAG_RD, &lastpid, 0, 
  161     "Last used PID");
  162 
  163 /*
  164  * Random component to lastpid generation.  We mix in a random factor to make
  165  * it a little harder to predict.  We sanity check the modulus value to avoid
  166  * doing it in critical paths.  Don't let it be too small or we pointlessly
  167  * waste randomness entropy, and don't let it be impossibly large.  Using a
  168  * modulus that is too big causes a LOT more process table scans and slows
  169  * down fork processing as the pidchecked caching is defeated.
  170  */
  171 static int randompid = 0;
  172 
  173 static int
  174 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
  175 {
  176         int error, pid;
  177 
  178         error = sysctl_wire_old_buffer(req, sizeof(int));
  179         if (error != 0)
  180                 return(error);
  181         sx_xlock(&allproc_lock);
  182         pid = randompid;
  183         error = sysctl_handle_int(oidp, &pid, 0, req);
  184         if (error == 0 && req->newptr != NULL) {
  185                 if (pid < 0 || pid > PID_MAX - 100)     /* out of range */
  186                         pid = PID_MAX - 100;
  187                 else if (pid < 2)                       /* NOP */
  188                         pid = 0;
  189                 else if (pid < 100)                     /* Make it reasonable */
  190                         pid = 100;
  191                 randompid = pid;
  192         }
  193         sx_xunlock(&allproc_lock);
  194         return (error);
  195 }
  196 
  197 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
  198     0, 0, sysctl_kern_randompid, "I", "Random PID modulus");
  199 
  200 int
  201 fork1(td, flags, pages, procp)
  202         struct thread *td;
  203         int flags;
  204         int pages;
  205         struct proc **procp;
  206 {
  207         struct proc *p1, *p2, *pptr;
  208         struct proc *newproc;
  209         int ok, trypid;
  210         static int curfail, pidchecked = 0;
  211         static struct timeval lastfail;
  212         struct filedesc *fd;
  213         struct filedesc_to_leader *fdtol;
  214         struct thread *td2;
  215         struct sigacts *newsigacts;
  216         struct vmspace *vm2;
  217         vm_ooffset_t mem_charged;
  218         int error;
  219 
  220         /* Can't copy and clear. */
  221         if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
  222                 return (EINVAL);
  223 
  224         p1 = td->td_proc;
  225 
  226         /*
  227          * Here we don't create a new process, but we divorce
  228          * certain parts of a process from itself.
  229          */
  230         if ((flags & RFPROC) == 0) {
  231                 if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
  232                     (flags & (RFCFDG | RFFDG))) {
  233                         PROC_LOCK(p1);
  234                         if (thread_single(SINGLE_BOUNDARY)) {
  235                                 PROC_UNLOCK(p1);
  236                                 return (ERESTART);
  237                         }
  238                         PROC_UNLOCK(p1);
  239                 }
  240 
  241                 error = vm_forkproc(td, NULL, NULL, NULL, flags);
  242                 if (error)
  243                         goto norfproc_fail;
  244 
  245                 /*
  246                  * Close all file descriptors.
  247                  */
  248                 if (flags & RFCFDG) {
  249                         struct filedesc *fdtmp;
  250                         fdtmp = fdinit(td->td_proc->p_fd);
  251                         fdfree(td);
  252                         p1->p_fd = fdtmp;
  253                 }
  254 
  255                 /*
  256                  * Unshare file descriptors (from parent).
  257                  */
  258                 if (flags & RFFDG) 
  259                         fdunshare(p1, td);
  260 
  261 norfproc_fail:
  262                 if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
  263                     (flags & (RFCFDG | RFFDG))) {
  264                         PROC_LOCK(p1);
  265                         thread_single_end();
  266                         PROC_UNLOCK(p1);
  267                 }
  268                 *procp = NULL;
  269                 return (error);
  270         }
  271 
  272         /*
  273          * XXX
  274          * We did have single-threading code here
  275          * however it proved un-needed and caused problems
  276          */
  277 
  278         mem_charged = 0;
  279         vm2 = NULL;
  280         if (pages == 0)
  281                 pages = KSTACK_PAGES;
  282         /* Allocate new proc. */
  283         newproc = uma_zalloc(proc_zone, M_WAITOK);
  284         td2 = FIRST_THREAD_IN_PROC(newproc);
  285         if (td2 == NULL) {
  286                 td2 = thread_alloc(pages);
  287                 if (td2 == NULL) {
  288                         error = ENOMEM;
  289                         goto fail1;
  290                 }
  291                 proc_linkup(newproc, td2);
  292         } else {
  293                 if (td2->td_kstack == 0 || td2->td_kstack_pages != pages) {
  294                         if (td2->td_kstack != 0)
  295                                 vm_thread_dispose(td2);
  296                         if (!thread_alloc_stack(td2, pages)) {
  297                                 error = ENOMEM;
  298                                 goto fail1;
  299                         }
  300                 }
  301         }
  302 
  303         if ((flags & RFMEM) == 0) {
  304                 vm2 = vmspace_fork(p1->p_vmspace, &mem_charged);
  305                 if (vm2 == NULL) {
  306                         error = ENOMEM;
  307                         goto fail1;
  308                 }
  309                 if (!swap_reserve(mem_charged)) {
  310                         /*
  311                          * The swap reservation failed. The accounting
  312                          * from the entries of the copied vm2 will be
  313                          * substracted in vmspace_free(), so force the
  314                          * reservation there.
  315                          */
  316                         swap_reserve_force(mem_charged);
  317                         error = ENOMEM;
  318                         goto fail1;
  319                 }
  320         } else
  321                 vm2 = NULL;
  322 #ifdef MAC
  323         mac_proc_init(newproc);
  324 #endif
  325         knlist_init_mtx(&newproc->p_klist, &newproc->p_mtx);
  326         STAILQ_INIT(&newproc->p_ktr);
  327 
  328         /* We have to lock the process tree while we look for a pid. */
  329         sx_slock(&proctree_lock);
  330 
  331         /*
  332          * Although process entries are dynamically created, we still keep
  333          * a global limit on the maximum number we will create.  Don't allow
  334          * a nonprivileged user to use the last ten processes; don't let root
  335          * exceed the limit. The variable nprocs is the current number of
  336          * processes, maxproc is the limit.
  337          */
  338         sx_xlock(&allproc_lock);
  339         if ((nprocs >= maxproc - 10 && priv_check_cred(td->td_ucred,
  340             PRIV_MAXPROC, 0) != 0) || nprocs >= maxproc) {
  341                 error = EAGAIN;
  342                 goto fail;
  343         }
  344 
  345         /*
  346          * Increment the count of procs running with this uid. Don't allow
  347          * a nonprivileged user to exceed their current limit.
  348          *
  349          * XXXRW: Can we avoid privilege here if it's not needed?
  350          */
  351         error = priv_check_cred(td->td_ucred, PRIV_PROC_LIMIT, 0);
  352         if (error == 0)
  353                 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1, 0);
  354         else {
  355                 PROC_LOCK(p1);
  356                 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1,
  357                     lim_cur(p1, RLIMIT_NPROC));
  358                 PROC_UNLOCK(p1);
  359         }
  360         if (!ok) {
  361                 error = EAGAIN;
  362                 goto fail;
  363         }
  364 
  365         /*
  366          * Increment the nprocs resource before blocking can occur.  There
  367          * are hard-limits as to the number of processes that can run.
  368          */
  369         nprocs++;
  370 
  371         /*
  372          * Find an unused process ID.  We remember a range of unused IDs
  373          * ready to use (from lastpid+1 through pidchecked-1).
  374          *
  375          * If RFHIGHPID is set (used during system boot), do not allocate
  376          * low-numbered pids.
  377          */
  378         trypid = lastpid + 1;
  379         if (flags & RFHIGHPID) {
  380                 if (trypid < 10)
  381                         trypid = 10;
  382         } else {
  383                 if (randompid)
  384                         trypid += arc4random() % randompid;
  385         }
  386 retry:
  387         /*
  388          * If the process ID prototype has wrapped around,
  389          * restart somewhat above 0, as the low-numbered procs
  390          * tend to include daemons that don't exit.
  391          */
  392         if (trypid >= PID_MAX) {
  393                 trypid = trypid % PID_MAX;
  394                 if (trypid < 100)
  395                         trypid += 100;
  396                 pidchecked = 0;
  397         }
  398         if (trypid >= pidchecked) {
  399                 int doingzomb = 0;
  400 
  401                 pidchecked = PID_MAX;
  402                 /*
  403                  * Scan the active and zombie procs to check whether this pid
  404                  * is in use.  Remember the lowest pid that's greater
  405                  * than trypid, so we can avoid checking for a while.
  406                  */
  407                 p2 = LIST_FIRST(&allproc);
  408 again:
  409                 for (; p2 != NULL; p2 = LIST_NEXT(p2, p_list)) {
  410                         while (p2->p_pid == trypid ||
  411                             (p2->p_pgrp != NULL &&
  412                             (p2->p_pgrp->pg_id == trypid ||
  413                             (p2->p_session != NULL &&
  414                             p2->p_session->s_sid == trypid)))) {
  415                                 trypid++;
  416                                 if (trypid >= pidchecked)
  417                                         goto retry;
  418                         }
  419                         if (p2->p_pid > trypid && pidchecked > p2->p_pid)
  420                                 pidchecked = p2->p_pid;
  421                         if (p2->p_pgrp != NULL) {
  422                                 if (p2->p_pgrp->pg_id > trypid &&
  423                                     pidchecked > p2->p_pgrp->pg_id)
  424                                         pidchecked = p2->p_pgrp->pg_id;
  425                                 if (p2->p_session != NULL &&
  426                                     p2->p_session->s_sid > trypid &&
  427                                     pidchecked > p2->p_session->s_sid)
  428                                         pidchecked = p2->p_session->s_sid;
  429                         }
  430                 }
  431                 if (!doingzomb) {
  432                         doingzomb = 1;
  433                         p2 = LIST_FIRST(&zombproc);
  434                         goto again;
  435                 }
  436         }
  437         sx_sunlock(&proctree_lock);
  438 
  439         /*
  440          * RFHIGHPID does not mess with the lastpid counter during boot.
  441          */
  442         if (flags & RFHIGHPID)
  443                 pidchecked = 0;
  444         else
  445                 lastpid = trypid;
  446 
  447         p2 = newproc;
  448         p2->p_state = PRS_NEW;          /* protect against others */
  449         p2->p_pid = trypid;
  450         /*
  451          * Allow the scheduler to initialize the child.
  452          */
  453         thread_lock(td);
  454         sched_fork(td, td2);
  455         thread_unlock(td);
  456         AUDIT_ARG_PID(p2->p_pid);
  457         LIST_INSERT_HEAD(&allproc, p2, p_list);
  458         LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
  459 
  460         PROC_LOCK(p2);
  461         PROC_LOCK(p1);
  462 
  463         sx_xunlock(&allproc_lock);
  464 
  465         bcopy(&p1->p_startcopy, &p2->p_startcopy,
  466             __rangeof(struct proc, p_startcopy, p_endcopy));
  467         pargs_hold(p2->p_args);
  468         PROC_UNLOCK(p1);
  469 
  470         bzero(&p2->p_startzero,
  471             __rangeof(struct proc, p_startzero, p_endzero));
  472 
  473         p2->p_ucred = crhold(td->td_ucred);
  474 
  475         /* Tell the prison that we exist. */
  476         prison_proc_hold(p2->p_ucred->cr_prison);
  477 
  478         PROC_UNLOCK(p2);
  479 
  480         /*
  481          * Malloc things while we don't hold any locks.
  482          */
  483         if (flags & RFSIGSHARE)
  484                 newsigacts = NULL;
  485         else
  486                 newsigacts = sigacts_alloc();
  487 
  488         /*
  489          * Copy filedesc.
  490          */
  491         if (flags & RFCFDG) {
  492                 fd = fdinit(p1->p_fd);
  493                 fdtol = NULL;
  494         } else if (flags & RFFDG) {
  495                 fd = fdcopy(p1->p_fd);
  496                 fdtol = NULL;
  497         } else {
  498                 fd = fdshare(p1->p_fd);
  499                 if (p1->p_fdtol == NULL)
  500                         p1->p_fdtol =
  501                                 filedesc_to_leader_alloc(NULL,
  502                                                          NULL,
  503                                                          p1->p_leader);
  504                 if ((flags & RFTHREAD) != 0) {
  505                         /*
  506                          * Shared file descriptor table and
  507                          * shared process leaders.
  508                          */
  509                         fdtol = p1->p_fdtol;
  510                         FILEDESC_XLOCK(p1->p_fd);
  511                         fdtol->fdl_refcount++;
  512                         FILEDESC_XUNLOCK(p1->p_fd);
  513                 } else {
  514                         /* 
  515                          * Shared file descriptor table, and
  516                          * different process leaders 
  517                          */
  518                         fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
  519                                                          p1->p_fd,
  520                                                          p2);
  521                 }
  522         }
  523         /*
  524          * Make a proc table entry for the new process.
  525          * Start by zeroing the section of proc that is zero-initialized,
  526          * then copy the section that is copied directly from the parent.
  527          */
  528 
  529         PROC_LOCK(p2);
  530         PROC_LOCK(p1);
  531 
  532         bzero(&td2->td_startzero,
  533             __rangeof(struct thread, td_startzero, td_endzero));
  534         bzero(&td2->td_rux, sizeof(td2->td_rux));
  535 
  536         bcopy(&td->td_startcopy, &td2->td_startcopy,
  537             __rangeof(struct thread, td_startcopy, td_endcopy));
  538 
  539         bcopy(&p2->p_comm, &td2->td_name, sizeof(td2->td_name));
  540         td2->td_sigstk = td->td_sigstk;
  541         td2->td_sigmask = td->td_sigmask;
  542         td2->td_flags = TDF_INMEM;
  543 
  544 #ifdef VIMAGE
  545         td2->td_vnet = NULL;
  546         td2->td_vnet_lpush = NULL;
  547 #endif
  548 
  549         /*
  550          * Duplicate sub-structures as needed.
  551          * Increase reference counts on shared objects.
  552          */
  553         p2->p_flag = P_INMEM;
  554         p2->p_swtick = ticks;
  555         if (p1->p_flag & P_PROFIL)
  556                 startprofclock(p2);
  557         td2->td_ucred = crhold(p2->p_ucred);
  558 
  559         if (flags & RFSIGSHARE) {
  560                 p2->p_sigacts = sigacts_hold(p1->p_sigacts);
  561         } else {
  562                 sigacts_copy(newsigacts, p1->p_sigacts);
  563                 p2->p_sigacts = newsigacts;
  564         }
  565         if (flags & RFLINUXTHPN) 
  566                 p2->p_sigparent = SIGUSR1;
  567         else
  568                 p2->p_sigparent = SIGCHLD;
  569 
  570         p2->p_textvp = p1->p_textvp;
  571         p2->p_fd = fd;
  572         p2->p_fdtol = fdtol;
  573 
  574         /*
  575          * p_limit is copy-on-write.  Bump its refcount.
  576          */
  577         lim_fork(p1, p2);
  578 
  579         pstats_fork(p1->p_stats, p2->p_stats);
  580 
  581         PROC_UNLOCK(p1);
  582         PROC_UNLOCK(p2);
  583 
  584         /* Bump references to the text vnode (for procfs) */
  585         if (p2->p_textvp)
  586                 vref(p2->p_textvp);
  587 
  588         /*
  589          * Set up linkage for kernel based threading.
  590          */
  591         if ((flags & RFTHREAD) != 0) {
  592                 mtx_lock(&ppeers_lock);
  593                 p2->p_peers = p1->p_peers;
  594                 p1->p_peers = p2;
  595                 p2->p_leader = p1->p_leader;
  596                 mtx_unlock(&ppeers_lock);
  597                 PROC_LOCK(p1->p_leader);
  598                 if ((p1->p_leader->p_flag & P_WEXIT) != 0) {
  599                         PROC_UNLOCK(p1->p_leader);
  600                         /*
  601                          * The task leader is exiting, so process p1 is
  602                          * going to be killed shortly.  Since p1 obviously
  603                          * isn't dead yet, we know that the leader is either
  604                          * sending SIGKILL's to all the processes in this
  605                          * task or is sleeping waiting for all the peers to
  606                          * exit.  We let p1 complete the fork, but we need
  607                          * to go ahead and kill the new process p2 since
  608                          * the task leader may not get a chance to send
  609                          * SIGKILL to it.  We leave it on the list so that
  610                          * the task leader will wait for this new process
  611                          * to commit suicide.
  612                          */
  613                         PROC_LOCK(p2);
  614                         psignal(p2, SIGKILL);
  615                         PROC_UNLOCK(p2);
  616                 } else
  617                         PROC_UNLOCK(p1->p_leader);
  618         } else {
  619                 p2->p_peers = NULL;
  620                 p2->p_leader = p2;
  621         }
  622 
  623         sx_xlock(&proctree_lock);
  624         PGRP_LOCK(p1->p_pgrp);
  625         PROC_LOCK(p2);
  626         PROC_LOCK(p1);
  627 
  628         /*
  629          * Preserve some more flags in subprocess.  P_PROFIL has already
  630          * been preserved.
  631          */
  632         p2->p_flag |= p1->p_flag & P_SUGID;
  633         td2->td_pflags |= td->td_pflags & TDP_ALTSTACK;
  634         SESS_LOCK(p1->p_session);
  635         if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
  636                 p2->p_flag |= P_CONTROLT;
  637         SESS_UNLOCK(p1->p_session);
  638         if (flags & RFPPWAIT)
  639                 p2->p_flag |= P_PPWAIT;
  640 
  641         p2->p_pgrp = p1->p_pgrp;
  642         LIST_INSERT_AFTER(p1, p2, p_pglist);
  643         PGRP_UNLOCK(p1->p_pgrp);
  644         LIST_INIT(&p2->p_children);
  645 
  646         callout_init(&p2->p_itcallout, CALLOUT_MPSAFE);
  647 
  648 #ifdef KTRACE
  649         /*
  650          * Copy traceflag and tracefile if enabled.
  651          */
  652         mtx_lock(&ktrace_mtx);
  653         KASSERT(p2->p_tracevp == NULL, ("new process has a ktrace vnode"));
  654         if (p1->p_traceflag & KTRFAC_INHERIT) {
  655                 p2->p_traceflag = p1->p_traceflag;
  656                 if ((p2->p_tracevp = p1->p_tracevp) != NULL) {
  657                         VREF(p2->p_tracevp);
  658                         KASSERT(p1->p_tracecred != NULL,
  659                             ("ktrace vnode with no cred"));
  660                         p2->p_tracecred = crhold(p1->p_tracecred);
  661                 }
  662         }
  663         mtx_unlock(&ktrace_mtx);
  664 #endif
  665 
  666         /*
  667          * If PF_FORK is set, the child process inherits the
  668          * procfs ioctl flags from its parent.
  669          */
  670         if (p1->p_pfsflags & PF_FORK) {
  671                 p2->p_stops = p1->p_stops;
  672                 p2->p_pfsflags = p1->p_pfsflags;
  673         }
  674 
  675 #ifdef KDTRACE_HOOKS
  676         /*
  677          * Tell the DTrace fasttrap provider about the new process
  678          * if it has registered an interest.
  679          */
  680         if (dtrace_fasttrap_fork)
  681                 dtrace_fasttrap_fork(p1, p2);
  682 #endif
  683 
  684         /*
  685          * This begins the section where we must prevent the parent
  686          * from being swapped.
  687          */
  688         _PHOLD(p1);
  689         PROC_UNLOCK(p1);
  690 
  691         /*
  692          * Attach the new process to its parent.
  693          *
  694          * If RFNOWAIT is set, the newly created process becomes a child
  695          * of init.  This effectively disassociates the child from the
  696          * parent.
  697          */
  698         if (flags & RFNOWAIT)
  699                 pptr = initproc;
  700         else
  701                 pptr = p1;
  702         p2->p_pptr = pptr;
  703         LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
  704         sx_xunlock(&proctree_lock);
  705 
  706         /* Inform accounting that we have forked. */
  707         p2->p_acflag = AFORK;
  708         PROC_UNLOCK(p2);
  709 
  710         /*
  711          * Finish creating the child process.  It will return via a different
  712          * execution path later.  (ie: directly into user mode)
  713          */
  714         vm_forkproc(td, p2, td2, vm2, flags);
  715 
  716         if (flags == (RFFDG | RFPROC)) {
  717                 PCPU_INC(cnt.v_forks);
  718                 PCPU_ADD(cnt.v_forkpages, p2->p_vmspace->vm_dsize +
  719                     p2->p_vmspace->vm_ssize);
  720         } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
  721                 PCPU_INC(cnt.v_vforks);
  722                 PCPU_ADD(cnt.v_vforkpages, p2->p_vmspace->vm_dsize +
  723                     p2->p_vmspace->vm_ssize);
  724         } else if (p1 == &proc0) {
  725                 PCPU_INC(cnt.v_kthreads);
  726                 PCPU_ADD(cnt.v_kthreadpages, p2->p_vmspace->vm_dsize +
  727                     p2->p_vmspace->vm_ssize);
  728         } else {
  729                 PCPU_INC(cnt.v_rforks);
  730                 PCPU_ADD(cnt.v_rforkpages, p2->p_vmspace->vm_dsize +
  731                     p2->p_vmspace->vm_ssize);
  732         }
  733 
  734         /*
  735          * Both processes are set up, now check if any loadable modules want
  736          * to adjust anything.
  737          *   What if they have an error? XXX
  738          */
  739         EVENTHANDLER_INVOKE(process_fork, p1, p2, flags);
  740 
  741         /*
  742          * Set the child start time and mark the process as being complete.
  743          */
  744         microuptime(&p2->p_stats->p_start);
  745         PROC_SLOCK(p2);
  746         p2->p_state = PRS_NORMAL;
  747         PROC_SUNLOCK(p2);
  748 
  749         /*
  750          * If RFSTOPPED not requested, make child runnable and add to
  751          * run queue.
  752          */
  753         if ((flags & RFSTOPPED) == 0) {
  754                 thread_lock(td2);
  755                 TD_SET_CAN_RUN(td2);
  756                 sched_add(td2, SRQ_BORING);
  757                 thread_unlock(td2);
  758         }
  759 
  760         /*
  761          * Now can be swapped.
  762          */
  763         PROC_LOCK(p1);
  764         _PRELE(p1);
  765         PROC_UNLOCK(p1);
  766 
  767         /*
  768          * Tell any interested parties about the new process.
  769          */
  770         knote_fork(&p1->p_klist, p2->p_pid);
  771         SDT_PROBE(proc, kernel, , create, p2, p1, flags, 0, 0);
  772 
  773         /*
  774          * Preserve synchronization semantics of vfork.  If waiting for
  775          * child to exec or exit, set P_PPWAIT on child, and sleep on our
  776          * proc (in case of exit).
  777          */
  778         PROC_LOCK(p2);
  779         while (p2->p_flag & P_PPWAIT)
  780                 cv_wait(&p2->p_pwait, &p2->p_mtx);
  781         PROC_UNLOCK(p2);
  782 
  783         /*
  784          * Return child proc pointer to parent.
  785          */
  786         *procp = p2;
  787         return (0);
  788 fail:
  789         sx_sunlock(&proctree_lock);
  790         if (ppsratecheck(&lastfail, &curfail, 1))
  791                 printf("maxproc limit exceeded by uid %i, please see tuning(7) and login.conf(5).\n",
  792                     td->td_ucred->cr_ruid);
  793         sx_xunlock(&allproc_lock);
  794 #ifdef MAC
  795         mac_proc_destroy(newproc);
  796 #endif
  797 fail1:
  798         if (vm2 != NULL)
  799                 vmspace_free(vm2);
  800         uma_zfree(proc_zone, newproc);
  801         pause("fork", hz / 2);
  802         return (error);
  803 }
  804 
  805 /*
  806  * Handle the return of a child process from fork1().  This function
  807  * is called from the MD fork_trampoline() entry point.
  808  */
  809 void
  810 fork_exit(callout, arg, frame)
  811         void (*callout)(void *, struct trapframe *);
  812         void *arg;
  813         struct trapframe *frame;
  814 {
  815         struct proc *p;
  816         struct thread *td;
  817         struct thread *dtd;
  818 
  819         td = curthread;
  820         p = td->td_proc;
  821         KASSERT(p->p_state == PRS_NORMAL, ("executing process is still new"));
  822 
  823         CTR4(KTR_PROC, "fork_exit: new thread %p (td_sched %p, pid %d, %s)",
  824                 td, td->td_sched, p->p_pid, td->td_name);
  825 
  826         sched_fork_exit(td);
  827         /*
  828         * Processes normally resume in mi_switch() after being
  829         * cpu_switch()'ed to, but when children start up they arrive here
  830         * instead, so we must do much the same things as mi_switch() would.
  831         */
  832         if ((dtd = PCPU_GET(deadthread))) {
  833                 PCPU_SET(deadthread, NULL);
  834                 thread_stash(dtd);
  835         }
  836         thread_unlock(td);
  837 
  838         /*
  839          * cpu_set_fork_handler intercepts this function call to
  840          * have this call a non-return function to stay in kernel mode.
  841          * initproc has its own fork handler, but it does return.
  842          */
  843         KASSERT(callout != NULL, ("NULL callout in fork_exit"));
  844         callout(arg, frame);
  845 
  846         /*
  847          * Check if a kernel thread misbehaved and returned from its main
  848          * function.
  849          */
  850         if (p->p_flag & P_KTHREAD) {
  851                 printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
  852                     td->td_name, p->p_pid);
  853                 kproc_exit(0);
  854         }
  855         mtx_assert(&Giant, MA_NOTOWNED);
  856 
  857         EVENTHANDLER_INVOKE(schedtail, p);
  858 }
  859 
  860 /*
  861  * Simplified back end of syscall(), used when returning from fork()
  862  * directly into user mode.  Giant is not held on entry, and must not
  863  * be held on return.  This function is passed in to fork_exit() as the
  864  * first parameter and is called when returning to a new userland process.
  865  */
  866 void
  867 fork_return(td, frame)
  868         struct thread *td;
  869         struct trapframe *frame;
  870 {
  871 
  872         userret(td, frame);
  873 #ifdef KTRACE
  874         if (KTRPOINT(td, KTR_SYSRET))
  875                 ktrsysret(SYS_fork, 0, 0);
  876 #endif
  877         mtx_assert(&Giant, MA_NOTOWNED);
  878 }

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