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/9.0/sys/kern/kern_fork.c 226092 2011-10-07 06:46:46Z trasz $");
   39 
   40 #include "opt_kdtrace.h"
   41 #include "opt_ktrace.h"
   42 #include "opt_kstack_pages.h"
   43 #include "opt_procdesc.h"
   44 
   45 #include <sys/param.h>
   46 #include <sys/systm.h>
   47 #include <sys/sysproto.h>
   48 #include <sys/eventhandler.h>
   49 #include <sys/fcntl.h>
   50 #include <sys/filedesc.h>
   51 #include <sys/jail.h>
   52 #include <sys/kernel.h>
   53 #include <sys/kthread.h>
   54 #include <sys/sysctl.h>
   55 #include <sys/lock.h>
   56 #include <sys/malloc.h>
   57 #include <sys/mutex.h>
   58 #include <sys/priv.h>
   59 #include <sys/proc.h>
   60 #include <sys/procdesc.h>
   61 #include <sys/pioctl.h>
   62 #include <sys/racct.h>
   63 #include <sys/resourcevar.h>
   64 #include <sys/sched.h>
   65 #include <sys/syscall.h>
   66 #include <sys/vmmeter.h>
   67 #include <sys/vnode.h>
   68 #include <sys/acct.h>
   69 #include <sys/ktr.h>
   70 #include <sys/ktrace.h>
   71 #include <sys/unistd.h> 
   72 #include <sys/sdt.h>
   73 #include <sys/sx.h>
   74 #include <sys/sysent.h>
   75 #include <sys/signalvar.h>
   76 
   77 #include <security/audit/audit.h>
   78 #include <security/mac/mac_framework.h>
   79 
   80 #include <vm/vm.h>
   81 #include <vm/pmap.h>
   82 #include <vm/vm_map.h>
   83 #include <vm/vm_extern.h>
   84 #include <vm/uma.h>
   85 
   86 #ifdef KDTRACE_HOOKS
   87 #include <sys/dtrace_bsd.h>
   88 dtrace_fork_func_t      dtrace_fasttrap_fork;
   89 #endif
   90 
   91 SDT_PROVIDER_DECLARE(proc);
   92 SDT_PROBE_DEFINE(proc, kernel, , create, create);
   93 SDT_PROBE_ARGTYPE(proc, kernel, , create, 0, "struct proc *");
   94 SDT_PROBE_ARGTYPE(proc, kernel, , create, 1, "struct proc *");
   95 SDT_PROBE_ARGTYPE(proc, kernel, , create, 2, "int");
   96 
   97 #ifndef _SYS_SYSPROTO_H_
   98 struct fork_args {
   99         int     dummy;
  100 };
  101 #endif
  102 
  103 /* ARGSUSED */
  104 int
  105 sys_fork(struct thread *td, struct fork_args *uap)
  106 {
  107         int error;
  108         struct proc *p2;
  109 
  110         error = fork1(td, RFFDG | RFPROC, 0, &p2, NULL, 0);
  111         if (error == 0) {
  112                 td->td_retval[0] = p2->p_pid;
  113                 td->td_retval[1] = 0;
  114         }
  115         return (error);
  116 }
  117 
  118 /* ARGUSED */
  119 int
  120 sys_pdfork(td, uap)
  121         struct thread *td;
  122         struct pdfork_args *uap;
  123 {
  124 #ifdef PROCDESC
  125         int error, fd;
  126         struct proc *p2;
  127 
  128         /*
  129          * It is necessary to return fd by reference because 0 is a valid file
  130          * descriptor number, and the child needs to be able to distinguish
  131          * itself from the parent using the return value.
  132          */
  133         error = fork1(td, RFFDG | RFPROC | RFPROCDESC, 0, &p2,
  134             &fd, uap->flags);
  135         if (error == 0) {
  136                 td->td_retval[0] = p2->p_pid;
  137                 td->td_retval[1] = 0;
  138                 error = copyout(&fd, uap->fdp, sizeof(fd));
  139         }
  140         return (error);
  141 #else
  142         return (ENOSYS);
  143 #endif
  144 }
  145 
  146 /* ARGSUSED */
  147 int
  148 sys_vfork(struct thread *td, struct vfork_args *uap)
  149 {
  150         int error, flags;
  151         struct proc *p2;
  152 
  153 #ifdef XEN
  154         flags = RFFDG | RFPROC; /* validate that this is still an issue */
  155 #else
  156         flags = RFFDG | RFPROC | RFPPWAIT | RFMEM;
  157 #endif          
  158         error = fork1(td, flags, 0, &p2, NULL, 0);
  159         if (error == 0) {
  160                 td->td_retval[0] = p2->p_pid;
  161                 td->td_retval[1] = 0;
  162         }
  163         return (error);
  164 }
  165 
  166 int
  167 sys_rfork(struct thread *td, struct rfork_args *uap)
  168 {
  169         struct proc *p2;
  170         int error;
  171 
  172         /* Don't allow kernel-only flags. */
  173         if ((uap->flags & RFKERNELONLY) != 0)
  174                 return (EINVAL);
  175 
  176         AUDIT_ARG_FFLAGS(uap->flags);
  177         error = fork1(td, uap->flags, 0, &p2, NULL, 0);
  178         if (error == 0) {
  179                 td->td_retval[0] = p2 ? p2->p_pid : 0;
  180                 td->td_retval[1] = 0;
  181         }
  182         return (error);
  183 }
  184 
  185 int     nprocs = 1;             /* process 0 */
  186 int     lastpid = 0;
  187 SYSCTL_INT(_kern, OID_AUTO, lastpid, CTLFLAG_RD, &lastpid, 0, 
  188     "Last used PID");
  189 
  190 /*
  191  * Random component to lastpid generation.  We mix in a random factor to make
  192  * it a little harder to predict.  We sanity check the modulus value to avoid
  193  * doing it in critical paths.  Don't let it be too small or we pointlessly
  194  * waste randomness entropy, and don't let it be impossibly large.  Using a
  195  * modulus that is too big causes a LOT more process table scans and slows
  196  * down fork processing as the pidchecked caching is defeated.
  197  */
  198 static int randompid = 0;
  199 
  200 static int
  201 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
  202 {
  203         int error, pid;
  204 
  205         error = sysctl_wire_old_buffer(req, sizeof(int));
  206         if (error != 0)
  207                 return(error);
  208         sx_xlock(&allproc_lock);
  209         pid = randompid;
  210         error = sysctl_handle_int(oidp, &pid, 0, req);
  211         if (error == 0 && req->newptr != NULL) {
  212                 if (pid < 0 || pid > PID_MAX - 100)     /* out of range */
  213                         pid = PID_MAX - 100;
  214                 else if (pid < 2)                       /* NOP */
  215                         pid = 0;
  216                 else if (pid < 100)                     /* Make it reasonable */
  217                         pid = 100;
  218                 randompid = pid;
  219         }
  220         sx_xunlock(&allproc_lock);
  221         return (error);
  222 }
  223 
  224 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
  225     0, 0, sysctl_kern_randompid, "I", "Random PID modulus");
  226 
  227 static int
  228 fork_findpid(int flags)
  229 {
  230         struct proc *p;
  231         int trypid;
  232         static int pidchecked = 0;
  233 
  234         /*
  235          * Requires allproc_lock in order to iterate over the list
  236          * of processes, and proctree_lock to access p_pgrp.
  237          */
  238         sx_assert(&allproc_lock, SX_LOCKED);
  239         sx_assert(&proctree_lock, SX_LOCKED);
  240 
  241         /*
  242          * Find an unused process ID.  We remember a range of unused IDs
  243          * ready to use (from lastpid+1 through pidchecked-1).
  244          *
  245          * If RFHIGHPID is set (used during system boot), do not allocate
  246          * low-numbered pids.
  247          */
  248         trypid = lastpid + 1;
  249         if (flags & RFHIGHPID) {
  250                 if (trypid < 10)
  251                         trypid = 10;
  252         } else {
  253                 if (randompid)
  254                         trypid += arc4random() % randompid;
  255         }
  256 retry:
  257         /*
  258          * If the process ID prototype has wrapped around,
  259          * restart somewhat above 0, as the low-numbered procs
  260          * tend to include daemons that don't exit.
  261          */
  262         if (trypid >= PID_MAX) {
  263                 trypid = trypid % PID_MAX;
  264                 if (trypid < 100)
  265                         trypid += 100;
  266                 pidchecked = 0;
  267         }
  268         if (trypid >= pidchecked) {
  269                 int doingzomb = 0;
  270 
  271                 pidchecked = PID_MAX;
  272                 /*
  273                  * Scan the active and zombie procs to check whether this pid
  274                  * is in use.  Remember the lowest pid that's greater
  275                  * than trypid, so we can avoid checking for a while.
  276                  */
  277                 p = LIST_FIRST(&allproc);
  278 again:
  279                 for (; p != NULL; p = LIST_NEXT(p, p_list)) {
  280                         while (p->p_pid == trypid ||
  281                             (p->p_pgrp != NULL &&
  282                             (p->p_pgrp->pg_id == trypid ||
  283                             (p->p_session != NULL &&
  284                             p->p_session->s_sid == trypid)))) {
  285                                 trypid++;
  286                                 if (trypid >= pidchecked)
  287                                         goto retry;
  288                         }
  289                         if (p->p_pid > trypid && pidchecked > p->p_pid)
  290                                 pidchecked = p->p_pid;
  291                         if (p->p_pgrp != NULL) {
  292                                 if (p->p_pgrp->pg_id > trypid &&
  293                                     pidchecked > p->p_pgrp->pg_id)
  294                                         pidchecked = p->p_pgrp->pg_id;
  295                                 if (p->p_session != NULL &&
  296                                     p->p_session->s_sid > trypid &&
  297                                     pidchecked > p->p_session->s_sid)
  298                                         pidchecked = p->p_session->s_sid;
  299                         }
  300                 }
  301                 if (!doingzomb) {
  302                         doingzomb = 1;
  303                         p = LIST_FIRST(&zombproc);
  304                         goto again;
  305                 }
  306         }
  307 
  308         /*
  309          * RFHIGHPID does not mess with the lastpid counter during boot.
  310          */
  311         if (flags & RFHIGHPID)
  312                 pidchecked = 0;
  313         else
  314                 lastpid = trypid;
  315 
  316         return (trypid);
  317 }
  318 
  319 static int
  320 fork_norfproc(struct thread *td, int flags)
  321 {
  322         int error;
  323         struct proc *p1;
  324 
  325         KASSERT((flags & RFPROC) == 0,
  326             ("fork_norfproc called with RFPROC set"));
  327         p1 = td->td_proc;
  328 
  329         if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
  330             (flags & (RFCFDG | RFFDG))) {
  331                 PROC_LOCK(p1);
  332                 if (thread_single(SINGLE_BOUNDARY)) {
  333                         PROC_UNLOCK(p1);
  334                         return (ERESTART);
  335                 }
  336                 PROC_UNLOCK(p1);
  337         }
  338 
  339         error = vm_forkproc(td, NULL, NULL, NULL, flags);
  340         if (error)
  341                 goto fail;
  342 
  343         /*
  344          * Close all file descriptors.
  345          */
  346         if (flags & RFCFDG) {
  347                 struct filedesc *fdtmp;
  348                 fdtmp = fdinit(td->td_proc->p_fd);
  349                 fdfree(td);
  350                 p1->p_fd = fdtmp;
  351         }
  352 
  353         /*
  354          * Unshare file descriptors (from parent).
  355          */
  356         if (flags & RFFDG) 
  357                 fdunshare(p1, td);
  358 
  359 fail:
  360         if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
  361             (flags & (RFCFDG | RFFDG))) {
  362                 PROC_LOCK(p1);
  363                 thread_single_end();
  364                 PROC_UNLOCK(p1);
  365         }
  366         return (error);
  367 }
  368 
  369 static void
  370 do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
  371     struct vmspace *vm2, int pdflags)
  372 {
  373         struct proc *p1, *pptr;
  374         int p2_held, trypid;
  375         struct filedesc *fd;
  376         struct filedesc_to_leader *fdtol;
  377         struct sigacts *newsigacts;
  378 
  379         sx_assert(&proctree_lock, SX_SLOCKED);
  380         sx_assert(&allproc_lock, SX_XLOCKED);
  381 
  382         p2_held = 0;
  383         p1 = td->td_proc;
  384 
  385         /*
  386          * Increment the nprocs resource before blocking can occur.  There
  387          * are hard-limits as to the number of processes that can run.
  388          */
  389         nprocs++;
  390 
  391         trypid = fork_findpid(flags);
  392 
  393         sx_sunlock(&proctree_lock);
  394 
  395         p2->p_state = PRS_NEW;          /* protect against others */
  396         p2->p_pid = trypid;
  397         AUDIT_ARG_PID(p2->p_pid);
  398         LIST_INSERT_HEAD(&allproc, p2, p_list);
  399         LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
  400         tidhash_add(td2);
  401         PROC_LOCK(p2);
  402         PROC_LOCK(p1);
  403 
  404         sx_xunlock(&allproc_lock);
  405 
  406         bcopy(&p1->p_startcopy, &p2->p_startcopy,
  407             __rangeof(struct proc, p_startcopy, p_endcopy));
  408         pargs_hold(p2->p_args);
  409         PROC_UNLOCK(p1);
  410 
  411         bzero(&p2->p_startzero,
  412             __rangeof(struct proc, p_startzero, p_endzero));
  413 
  414         p2->p_ucred = crhold(td->td_ucred);
  415 
  416         /* Tell the prison that we exist. */
  417         prison_proc_hold(p2->p_ucred->cr_prison);
  418 
  419         PROC_UNLOCK(p2);
  420 
  421         /*
  422          * Malloc things while we don't hold any locks.
  423          */
  424         if (flags & RFSIGSHARE)
  425                 newsigacts = NULL;
  426         else
  427                 newsigacts = sigacts_alloc();
  428 
  429         /*
  430          * Copy filedesc.
  431          */
  432         if (flags & RFCFDG) {
  433                 fd = fdinit(p1->p_fd);
  434                 fdtol = NULL;
  435         } else if (flags & RFFDG) {
  436                 fd = fdcopy(p1->p_fd);
  437                 fdtol = NULL;
  438         } else {
  439                 fd = fdshare(p1->p_fd);
  440                 if (p1->p_fdtol == NULL)
  441                         p1->p_fdtol = filedesc_to_leader_alloc(NULL, NULL,
  442                             p1->p_leader);
  443                 if ((flags & RFTHREAD) != 0) {
  444                         /*
  445                          * Shared file descriptor table, and shared
  446                          * process leaders.
  447                          */
  448                         fdtol = p1->p_fdtol;
  449                         FILEDESC_XLOCK(p1->p_fd);
  450                         fdtol->fdl_refcount++;
  451                         FILEDESC_XUNLOCK(p1->p_fd);
  452                 } else {
  453                         /* 
  454                          * Shared file descriptor table, and different
  455                          * process leaders.
  456                          */
  457                         fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
  458                             p1->p_fd, p2);
  459                 }
  460         }
  461         /*
  462          * Make a proc table entry for the new process.
  463          * Start by zeroing the section of proc that is zero-initialized,
  464          * then copy the section that is copied directly from the parent.
  465          */
  466 
  467         PROC_LOCK(p2);
  468         PROC_LOCK(p1);
  469 
  470         bzero(&td2->td_startzero,
  471             __rangeof(struct thread, td_startzero, td_endzero));
  472 
  473         bcopy(&td->td_startcopy, &td2->td_startcopy,
  474             __rangeof(struct thread, td_startcopy, td_endcopy));
  475 
  476         bcopy(&p2->p_comm, &td2->td_name, sizeof(td2->td_name));
  477         td2->td_sigstk = td->td_sigstk;
  478         td2->td_sigmask = td->td_sigmask;
  479         td2->td_flags = TDF_INMEM;
  480         td2->td_lend_user_pri = PRI_MAX;
  481 
  482 #ifdef VIMAGE
  483         td2->td_vnet = NULL;
  484         td2->td_vnet_lpush = NULL;
  485 #endif
  486 
  487         /*
  488          * Allow the scheduler to initialize the child.
  489          */
  490         thread_lock(td);
  491         sched_fork(td, td2);
  492         thread_unlock(td);
  493 
  494         /*
  495          * Duplicate sub-structures as needed.
  496          * Increase reference counts on shared objects.
  497          */
  498         p2->p_flag = P_INMEM;
  499         p2->p_swtick = ticks;
  500         if (p1->p_flag & P_PROFIL)
  501                 startprofclock(p2);
  502         td2->td_ucred = crhold(p2->p_ucred);
  503 
  504         if (flags & RFSIGSHARE) {
  505                 p2->p_sigacts = sigacts_hold(p1->p_sigacts);
  506         } else {
  507                 sigacts_copy(newsigacts, p1->p_sigacts);
  508                 p2->p_sigacts = newsigacts;
  509         }
  510 
  511         if (flags & RFTSIGZMB)
  512                 p2->p_sigparent = RFTSIGNUM(flags);
  513         else if (flags & RFLINUXTHPN)
  514                 p2->p_sigparent = SIGUSR1;
  515         else
  516                 p2->p_sigparent = SIGCHLD;
  517 
  518         p2->p_textvp = p1->p_textvp;
  519         p2->p_fd = fd;
  520         p2->p_fdtol = fdtol;
  521 
  522         /*
  523          * p_limit is copy-on-write.  Bump its refcount.
  524          */
  525         lim_fork(p1, p2);
  526 
  527         pstats_fork(p1->p_stats, p2->p_stats);
  528 
  529         PROC_UNLOCK(p1);
  530         PROC_UNLOCK(p2);
  531 
  532         /* Bump references to the text vnode (for procfs). */
  533         if (p2->p_textvp)
  534                 vref(p2->p_textvp);
  535 
  536         /*
  537          * Set up linkage for kernel based threading.
  538          */
  539         if ((flags & RFTHREAD) != 0) {
  540                 mtx_lock(&ppeers_lock);
  541                 p2->p_peers = p1->p_peers;
  542                 p1->p_peers = p2;
  543                 p2->p_leader = p1->p_leader;
  544                 mtx_unlock(&ppeers_lock);
  545                 PROC_LOCK(p1->p_leader);
  546                 if ((p1->p_leader->p_flag & P_WEXIT) != 0) {
  547                         PROC_UNLOCK(p1->p_leader);
  548                         /*
  549                          * The task leader is exiting, so process p1 is
  550                          * going to be killed shortly.  Since p1 obviously
  551                          * isn't dead yet, we know that the leader is either
  552                          * sending SIGKILL's to all the processes in this
  553                          * task or is sleeping waiting for all the peers to
  554                          * exit.  We let p1 complete the fork, but we need
  555                          * to go ahead and kill the new process p2 since
  556                          * the task leader may not get a chance to send
  557                          * SIGKILL to it.  We leave it on the list so that
  558                          * the task leader will wait for this new process
  559                          * to commit suicide.
  560                          */
  561                         PROC_LOCK(p2);
  562                         kern_psignal(p2, SIGKILL);
  563                         PROC_UNLOCK(p2);
  564                 } else
  565                         PROC_UNLOCK(p1->p_leader);
  566         } else {
  567                 p2->p_peers = NULL;
  568                 p2->p_leader = p2;
  569         }
  570 
  571         sx_xlock(&proctree_lock);
  572         PGRP_LOCK(p1->p_pgrp);
  573         PROC_LOCK(p2);
  574         PROC_LOCK(p1);
  575 
  576         /*
  577          * Preserve some more flags in subprocess.  P_PROFIL has already
  578          * been preserved.
  579          */
  580         p2->p_flag |= p1->p_flag & P_SUGID;
  581         td2->td_pflags |= td->td_pflags & TDP_ALTSTACK;
  582         SESS_LOCK(p1->p_session);
  583         if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
  584                 p2->p_flag |= P_CONTROLT;
  585         SESS_UNLOCK(p1->p_session);
  586         if (flags & RFPPWAIT)
  587                 p2->p_flag |= P_PPWAIT;
  588 
  589         p2->p_pgrp = p1->p_pgrp;
  590         LIST_INSERT_AFTER(p1, p2, p_pglist);
  591         PGRP_UNLOCK(p1->p_pgrp);
  592         LIST_INIT(&p2->p_children);
  593 
  594         callout_init(&p2->p_itcallout, CALLOUT_MPSAFE);
  595 
  596         /*
  597          * If PF_FORK is set, the child process inherits the
  598          * procfs ioctl flags from its parent.
  599          */
  600         if (p1->p_pfsflags & PF_FORK) {
  601                 p2->p_stops = p1->p_stops;
  602                 p2->p_pfsflags = p1->p_pfsflags;
  603         }
  604 
  605         /*
  606          * This begins the section where we must prevent the parent
  607          * from being swapped.
  608          */
  609         _PHOLD(p1);
  610         PROC_UNLOCK(p1);
  611 
  612         /*
  613          * Attach the new process to its parent.
  614          *
  615          * If RFNOWAIT is set, the newly created process becomes a child
  616          * of init.  This effectively disassociates the child from the
  617          * parent.
  618          */
  619         if (flags & RFNOWAIT)
  620                 pptr = initproc;
  621         else
  622                 pptr = p1;
  623         p2->p_pptr = pptr;
  624         LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
  625         sx_xunlock(&proctree_lock);
  626 
  627         /* Inform accounting that we have forked. */
  628         p2->p_acflag = AFORK;
  629         PROC_UNLOCK(p2);
  630 
  631 #ifdef KTRACE
  632         ktrprocfork(p1, p2);
  633 #endif
  634 
  635         /*
  636          * Finish creating the child process.  It will return via a different
  637          * execution path later.  (ie: directly into user mode)
  638          */
  639         vm_forkproc(td, p2, td2, vm2, flags);
  640 
  641         if (flags == (RFFDG | RFPROC)) {
  642                 PCPU_INC(cnt.v_forks);
  643                 PCPU_ADD(cnt.v_forkpages, p2->p_vmspace->vm_dsize +
  644                     p2->p_vmspace->vm_ssize);
  645         } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
  646                 PCPU_INC(cnt.v_vforks);
  647                 PCPU_ADD(cnt.v_vforkpages, p2->p_vmspace->vm_dsize +
  648                     p2->p_vmspace->vm_ssize);
  649         } else if (p1 == &proc0) {
  650                 PCPU_INC(cnt.v_kthreads);
  651                 PCPU_ADD(cnt.v_kthreadpages, p2->p_vmspace->vm_dsize +
  652                     p2->p_vmspace->vm_ssize);
  653         } else {
  654                 PCPU_INC(cnt.v_rforks);
  655                 PCPU_ADD(cnt.v_rforkpages, p2->p_vmspace->vm_dsize +
  656                     p2->p_vmspace->vm_ssize);
  657         }
  658 
  659 #ifdef PROCDESC
  660         /*
  661          * Associate the process descriptor with the process before anything
  662          * can happen that might cause that process to need the descriptor.
  663          * However, don't do this until after fork(2) can no longer fail.
  664          */
  665         if (flags & RFPROCDESC)
  666                 procdesc_new(p2, pdflags);
  667 #endif
  668 
  669         /*
  670          * Both processes are set up, now check if any loadable modules want
  671          * to adjust anything.
  672          */
  673         EVENTHANDLER_INVOKE(process_fork, p1, p2, flags);
  674 
  675         /*
  676          * Set the child start time and mark the process as being complete.
  677          */
  678         PROC_LOCK(p2);
  679         PROC_LOCK(p1);
  680         microuptime(&p2->p_stats->p_start);
  681         PROC_SLOCK(p2);
  682         p2->p_state = PRS_NORMAL;
  683         PROC_SUNLOCK(p2);
  684 
  685 #ifdef KDTRACE_HOOKS
  686         /*
  687          * Tell the DTrace fasttrap provider about the new process
  688          * if it has registered an interest. We have to do this only after
  689          * p_state is PRS_NORMAL since the fasttrap module will use pfind()
  690          * later on.
  691          */
  692         if (dtrace_fasttrap_fork)
  693                 dtrace_fasttrap_fork(p1, p2);
  694 #endif
  695         if ((p1->p_flag & (P_TRACED | P_FOLLOWFORK)) == (P_TRACED |
  696             P_FOLLOWFORK)) {
  697                 /*
  698                  * Arrange for debugger to receive the fork event.
  699                  *
  700                  * We can report PL_FLAG_FORKED regardless of
  701                  * P_FOLLOWFORK settings, but it does not make a sense
  702                  * for runaway child.
  703                  */
  704                 td->td_dbgflags |= TDB_FORK;
  705                 td->td_dbg_forked = p2->p_pid;
  706                 td2->td_dbgflags |= TDB_STOPATFORK;
  707                 _PHOLD(p2);
  708                 p2_held = 1;
  709         }
  710         PROC_UNLOCK(p2);
  711         if ((flags & RFSTOPPED) == 0) {
  712                 /*
  713                  * If RFSTOPPED not requested, make child runnable and
  714                  * add to run queue.
  715                  */
  716                 thread_lock(td2);
  717                 TD_SET_CAN_RUN(td2);
  718                 sched_add(td2, SRQ_BORING);
  719                 thread_unlock(td2);
  720         }
  721 
  722         /*
  723          * Now can be swapped.
  724          */
  725         _PRELE(p1);
  726         PROC_UNLOCK(p1);
  727 
  728         /*
  729          * Tell any interested parties about the new process.
  730          */
  731         knote_fork(&p1->p_klist, p2->p_pid);
  732         SDT_PROBE(proc, kernel, , create, p2, p1, flags, 0, 0);
  733 
  734         /*
  735          * Wait until debugger is attached to child.
  736          */
  737         PROC_LOCK(p2);
  738         while ((td2->td_dbgflags & TDB_STOPATFORK) != 0)
  739                 cv_wait(&p2->p_dbgwait, &p2->p_mtx);
  740         if (p2_held)
  741                 _PRELE(p2);
  742 
  743         /*
  744          * Preserve synchronization semantics of vfork.  If waiting for
  745          * child to exec or exit, set P_PPWAIT on child, and sleep on our
  746          * proc (in case of exit).
  747          */
  748         while (p2->p_flag & P_PPWAIT)
  749                 cv_wait(&p2->p_pwait, &p2->p_mtx);
  750         PROC_UNLOCK(p2);
  751 }
  752 
  753 int
  754 fork1(struct thread *td, int flags, int pages, struct proc **procp,
  755     int *procdescp, int pdflags)
  756 {
  757         struct proc *p1;
  758         struct proc *newproc;
  759         int ok;
  760         struct thread *td2;
  761         struct vmspace *vm2;
  762         vm_ooffset_t mem_charged;
  763         int error;
  764         static int curfail;
  765         static struct timeval lastfail;
  766 #ifdef PROCDESC
  767         struct file *fp_procdesc = NULL;
  768 #endif
  769 
  770         /* Check for the undefined or unimplemented flags. */
  771         if ((flags & ~(RFFLAGS | RFTSIGFLAGS(RFTSIGMASK))) != 0)
  772                 return (EINVAL);
  773 
  774         /* Signal value requires RFTSIGZMB. */
  775         if ((flags & RFTSIGFLAGS(RFTSIGMASK)) != 0 && (flags & RFTSIGZMB) == 0)
  776                 return (EINVAL);
  777 
  778         /* Can't copy and clear. */
  779         if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
  780                 return (EINVAL);
  781 
  782         /* Check the validity of the signal number. */
  783         if ((flags & RFTSIGZMB) != 0 && (u_int)RFTSIGNUM(flags) > _SIG_MAXSIG)
  784                 return (EINVAL);
  785 
  786 #ifdef PROCDESC
  787         if ((flags & RFPROCDESC) != 0) {
  788                 /* Can't not create a process yet get a process descriptor. */
  789                 if ((flags & RFPROC) == 0)
  790                         return (EINVAL);
  791 
  792                 /* Must provide a place to put a procdesc if creating one. */
  793                 if (procdescp == NULL)
  794                         return (EINVAL);
  795         }
  796 #endif
  797 
  798         p1 = td->td_proc;
  799 
  800         /*
  801          * Here we don't create a new process, but we divorce
  802          * certain parts of a process from itself.
  803          */
  804         if ((flags & RFPROC) == 0) {
  805                 *procp = NULL;
  806                 return (fork_norfproc(td, flags));
  807         }
  808 
  809 #ifdef PROCDESC
  810         /*
  811          * If required, create a process descriptor in the parent first; we
  812          * will abandon it if something goes wrong. We don't finit() until
  813          * later.
  814          */
  815         if (flags & RFPROCDESC) {
  816                 error = falloc(td, &fp_procdesc, procdescp, 0);
  817                 if (error != 0)
  818                         return (error);
  819         }
  820 #endif
  821 
  822         mem_charged = 0;
  823         vm2 = NULL;
  824         if (pages == 0)
  825                 pages = KSTACK_PAGES;
  826         /* Allocate new proc. */
  827         newproc = uma_zalloc(proc_zone, M_WAITOK);
  828         td2 = FIRST_THREAD_IN_PROC(newproc);
  829         if (td2 == NULL) {
  830                 td2 = thread_alloc(pages);
  831                 if (td2 == NULL) {
  832                         error = ENOMEM;
  833                         goto fail1;
  834                 }
  835                 proc_linkup(newproc, td2);
  836         } else {
  837                 if (td2->td_kstack == 0 || td2->td_kstack_pages != pages) {
  838                         if (td2->td_kstack != 0)
  839                                 vm_thread_dispose(td2);
  840                         if (!thread_alloc_stack(td2, pages)) {
  841                                 error = ENOMEM;
  842                                 goto fail1;
  843                         }
  844                 }
  845         }
  846 
  847         if ((flags & RFMEM) == 0) {
  848                 vm2 = vmspace_fork(p1->p_vmspace, &mem_charged);
  849                 if (vm2 == NULL) {
  850                         error = ENOMEM;
  851                         goto fail1;
  852                 }
  853                 if (!swap_reserve(mem_charged)) {
  854                         /*
  855                          * The swap reservation failed. The accounting
  856                          * from the entries of the copied vm2 will be
  857                          * substracted in vmspace_free(), so force the
  858                          * reservation there.
  859                          */
  860                         swap_reserve_force(mem_charged);
  861                         error = ENOMEM;
  862                         goto fail1;
  863                 }
  864         } else
  865                 vm2 = NULL;
  866 
  867         /*
  868          * XXX: This is ugly; when we copy resource usage, we need to bump
  869          *      per-cred resource counters.
  870          */
  871         newproc->p_ucred = p1->p_ucred;
  872 
  873         /*
  874          * Initialize resource accounting for the child process.
  875          */
  876         error = racct_proc_fork(p1, newproc);
  877         if (error != 0) {
  878                 error = EAGAIN;
  879                 goto fail1;
  880         }
  881 
  882 #ifdef MAC
  883         mac_proc_init(newproc);
  884 #endif
  885         knlist_init_mtx(&newproc->p_klist, &newproc->p_mtx);
  886         STAILQ_INIT(&newproc->p_ktr);
  887 
  888         /* We have to lock the process tree while we look for a pid. */
  889         sx_slock(&proctree_lock);
  890 
  891         /*
  892          * Although process entries are dynamically created, we still keep
  893          * a global limit on the maximum number we will create.  Don't allow
  894          * a nonprivileged user to use the last ten processes; don't let root
  895          * exceed the limit. The variable nprocs is the current number of
  896          * processes, maxproc is the limit.
  897          */
  898         sx_xlock(&allproc_lock);
  899         if ((nprocs >= maxproc - 10 && priv_check_cred(td->td_ucred,
  900             PRIV_MAXPROC, 0) != 0) || nprocs >= maxproc) {
  901                 error = EAGAIN;
  902                 goto fail;
  903         }
  904 
  905         /*
  906          * Increment the count of procs running with this uid. Don't allow
  907          * a nonprivileged user to exceed their current limit.
  908          *
  909          * XXXRW: Can we avoid privilege here if it's not needed?
  910          */
  911         error = priv_check_cred(td->td_ucred, PRIV_PROC_LIMIT, 0);
  912         if (error == 0)
  913                 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1, 0);
  914         else {
  915                 PROC_LOCK(p1);
  916                 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1,
  917                     lim_cur(p1, RLIMIT_NPROC));
  918                 PROC_UNLOCK(p1);
  919         }
  920         if (ok) {
  921                 do_fork(td, flags, newproc, td2, vm2, pdflags);
  922 
  923                 /*
  924                  * Return child proc pointer to parent.
  925                  */
  926                 *procp = newproc;
  927 #ifdef PROCDESC
  928                 if (flags & RFPROCDESC)
  929                         procdesc_finit(newproc->p_procdesc, fp_procdesc);
  930 #endif
  931                 racct_proc_fork_done(newproc);
  932                 return (0);
  933         }
  934 
  935         error = EAGAIN;
  936 fail:
  937         sx_sunlock(&proctree_lock);
  938         if (ppsratecheck(&lastfail, &curfail, 1))
  939                 printf("maxproc limit exceeded by uid %i, please see tuning(7) and login.conf(5).\n",
  940                     td->td_ucred->cr_ruid);
  941         sx_xunlock(&allproc_lock);
  942 #ifdef MAC
  943         mac_proc_destroy(newproc);
  944 #endif
  945 fail1:
  946         racct_proc_exit(newproc);
  947         if (vm2 != NULL)
  948                 vmspace_free(vm2);
  949         uma_zfree(proc_zone, newproc);
  950 #ifdef PROCDESC
  951         if (((flags & RFPROCDESC) != 0) && (fp_procdesc != NULL))
  952                 fdrop(fp_procdesc, td);
  953 #endif
  954         pause("fork", hz / 2);
  955         return (error);
  956 }
  957 
  958 /*
  959  * Handle the return of a child process from fork1().  This function
  960  * is called from the MD fork_trampoline() entry point.
  961  */
  962 void
  963 fork_exit(void (*callout)(void *, struct trapframe *), void *arg,
  964     struct trapframe *frame)
  965 {
  966         struct proc *p;
  967         struct thread *td;
  968         struct thread *dtd;
  969 
  970         td = curthread;
  971         p = td->td_proc;
  972         KASSERT(p->p_state == PRS_NORMAL, ("executing process is still new"));
  973 
  974         CTR4(KTR_PROC, "fork_exit: new thread %p (td_sched %p, pid %d, %s)",
  975                 td, td->td_sched, p->p_pid, td->td_name);
  976 
  977         sched_fork_exit(td);
  978         /*
  979         * Processes normally resume in mi_switch() after being
  980         * cpu_switch()'ed to, but when children start up they arrive here
  981         * instead, so we must do much the same things as mi_switch() would.
  982         */
  983         if ((dtd = PCPU_GET(deadthread))) {
  984                 PCPU_SET(deadthread, NULL);
  985                 thread_stash(dtd);
  986         }
  987         thread_unlock(td);
  988 
  989         /*
  990          * cpu_set_fork_handler intercepts this function call to
  991          * have this call a non-return function to stay in kernel mode.
  992          * initproc has its own fork handler, but it does return.
  993          */
  994         KASSERT(callout != NULL, ("NULL callout in fork_exit"));
  995         callout(arg, frame);
  996 
  997         /*
  998          * Check if a kernel thread misbehaved and returned from its main
  999          * function.
 1000          */
 1001         if (p->p_flag & P_KTHREAD) {
 1002                 printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
 1003                     td->td_name, p->p_pid);
 1004                 kproc_exit(0);
 1005         }
 1006         mtx_assert(&Giant, MA_NOTOWNED);
 1007 
 1008         if (p->p_sysent->sv_schedtail != NULL)
 1009                 (p->p_sysent->sv_schedtail)(td);
 1010 }
 1011 
 1012 /*
 1013  * Simplified back end of syscall(), used when returning from fork()
 1014  * directly into user mode.  Giant is not held on entry, and must not
 1015  * be held on return.  This function is passed in to fork_exit() as the
 1016  * first parameter and is called when returning to a new userland process.
 1017  */
 1018 void
 1019 fork_return(struct thread *td, struct trapframe *frame)
 1020 {
 1021         struct proc *p, *dbg;
 1022 
 1023         if (td->td_dbgflags & TDB_STOPATFORK) {
 1024                 p = td->td_proc;
 1025                 sx_xlock(&proctree_lock);
 1026                 PROC_LOCK(p);
 1027                 if ((p->p_pptr->p_flag & (P_TRACED | P_FOLLOWFORK)) ==
 1028                     (P_TRACED | P_FOLLOWFORK)) {
 1029                         /*
 1030                          * If debugger still wants auto-attach for the
 1031                          * parent's children, do it now.
 1032                          */
 1033                         dbg = p->p_pptr->p_pptr;
 1034                         p->p_flag |= P_TRACED;
 1035                         p->p_oppid = p->p_pptr->p_pid;
 1036                         proc_reparent(p, dbg);
 1037                         sx_xunlock(&proctree_lock);
 1038                         ptracestop(td, SIGSTOP);
 1039                 } else {
 1040                         /*
 1041                          * ... otherwise clear the request.
 1042                          */
 1043                         sx_xunlock(&proctree_lock);
 1044                         td->td_dbgflags &= ~TDB_STOPATFORK;
 1045                         cv_broadcast(&p->p_dbgwait);
 1046                 }
 1047                 PROC_UNLOCK(p);
 1048         }
 1049 
 1050         userret(td, frame);
 1051 
 1052 #ifdef KTRACE
 1053         if (KTRPOINT(td, KTR_SYSRET))
 1054                 ktrsysret(SYS_fork, 0, 0);
 1055 #endif
 1056         mtx_assert(&Giant, MA_NOTOWNED);
 1057 }

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