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: stable/10/sys/kern/kern_fork.c 321020 2017-07-15 17:25:40Z dchagin $");
   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/ptrace.h>
   63 #include <sys/racct.h>
   64 #include <sys/resourcevar.h>
   65 #include <sys/sched.h>
   66 #include <sys/syscall.h>
   67 #include <sys/vmmeter.h>
   68 #include <sys/vnode.h>
   69 #include <sys/acct.h>
   70 #include <sys/ktr.h>
   71 #include <sys/ktrace.h>
   72 #include <sys/unistd.h> 
   73 #include <sys/sdt.h>
   74 #include <sys/sx.h>
   75 #include <sys/sysent.h>
   76 #include <sys/signalvar.h>
   77 
   78 #include <security/audit/audit.h>
   79 #include <security/mac/mac_framework.h>
   80 
   81 #include <vm/vm.h>
   82 #include <vm/pmap.h>
   83 #include <vm/vm_map.h>
   84 #include <vm/vm_extern.h>
   85 #include <vm/uma.h>
   86 
   87 #ifdef KDTRACE_HOOKS
   88 #include <sys/dtrace_bsd.h>
   89 dtrace_fork_func_t      dtrace_fasttrap_fork;
   90 #endif
   91 
   92 SDT_PROVIDER_DECLARE(proc);
   93 SDT_PROBE_DEFINE3(proc, , , create, "struct proc *", "struct proc *", "int");
   94 
   95 #ifndef _SYS_SYSPROTO_H_
   96 struct fork_args {
   97         int     dummy;
   98 };
   99 #endif
  100 
  101 /* ARGSUSED */
  102 int
  103 sys_fork(struct thread *td, struct fork_args *uap)
  104 {
  105         int error;
  106         struct proc *p2;
  107 
  108         error = fork1(td, RFFDG | RFPROC, 0, &p2, NULL, 0);
  109         if (error == 0) {
  110                 td->td_retval[0] = p2->p_pid;
  111                 td->td_retval[1] = 0;
  112         }
  113         return (error);
  114 }
  115 
  116 /* ARGUSED */
  117 int
  118 sys_pdfork(td, uap)
  119         struct thread *td;
  120         struct pdfork_args *uap;
  121 {
  122 #ifdef PROCDESC
  123         int error, fd;
  124         struct proc *p2;
  125 
  126         /*
  127          * It is necessary to return fd by reference because 0 is a valid file
  128          * descriptor number, and the child needs to be able to distinguish
  129          * itself from the parent using the return value.
  130          */
  131         error = fork1(td, RFFDG | RFPROC | RFPROCDESC, 0, &p2,
  132             &fd, uap->flags);
  133         if (error == 0) {
  134                 td->td_retval[0] = p2->p_pid;
  135                 td->td_retval[1] = 0;
  136                 error = copyout(&fd, uap->fdp, sizeof(fd));
  137         }
  138         return (error);
  139 #else
  140         return (ENOSYS);
  141 #endif
  142 }
  143 
  144 /* ARGSUSED */
  145 int
  146 sys_vfork(struct thread *td, struct vfork_args *uap)
  147 {
  148         int error, flags;
  149         struct proc *p2;
  150 
  151         flags = RFFDG | RFPROC | RFPPWAIT | RFMEM;
  152         error = fork1(td, flags, 0, &p2, NULL, 0);
  153         if (error == 0) {
  154                 td->td_retval[0] = p2->p_pid;
  155                 td->td_retval[1] = 0;
  156         }
  157         return (error);
  158 }
  159 
  160 int
  161 sys_rfork(struct thread *td, struct rfork_args *uap)
  162 {
  163         struct proc *p2;
  164         int error;
  165 
  166         /* Don't allow kernel-only flags. */
  167         if ((uap->flags & RFKERNELONLY) != 0)
  168                 return (EINVAL);
  169 
  170         AUDIT_ARG_FFLAGS(uap->flags);
  171         error = fork1(td, uap->flags, 0, &p2, NULL, 0);
  172         if (error == 0) {
  173                 td->td_retval[0] = p2 ? p2->p_pid : 0;
  174                 td->td_retval[1] = 0;
  175         }
  176         return (error);
  177 }
  178 
  179 int     nprocs = 1;             /* process 0 */
  180 int     lastpid = 0;
  181 SYSCTL_INT(_kern, OID_AUTO, lastpid, CTLFLAG_RD, &lastpid, 0, 
  182     "Last used PID");
  183 
  184 /*
  185  * Random component to lastpid generation.  We mix in a random factor to make
  186  * it a little harder to predict.  We sanity check the modulus value to avoid
  187  * doing it in critical paths.  Don't let it be too small or we pointlessly
  188  * waste randomness entropy, and don't let it be impossibly large.  Using a
  189  * modulus that is too big causes a LOT more process table scans and slows
  190  * down fork processing as the pidchecked caching is defeated.
  191  */
  192 static int randompid = 0;
  193 
  194 static int
  195 sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
  196 {
  197         int error, pid;
  198 
  199         error = sysctl_wire_old_buffer(req, sizeof(int));
  200         if (error != 0)
  201                 return(error);
  202         sx_xlock(&allproc_lock);
  203         pid = randompid;
  204         error = sysctl_handle_int(oidp, &pid, 0, req);
  205         if (error == 0 && req->newptr != NULL) {
  206                 if (pid < 0 || pid > pid_max - 100)     /* out of range */
  207                         pid = pid_max - 100;
  208                 else if (pid < 2)                       /* NOP */
  209                         pid = 0;
  210                 else if (pid < 100)                     /* Make it reasonable */
  211                         pid = 100;
  212                 randompid = pid;
  213         }
  214         sx_xunlock(&allproc_lock);
  215         return (error);
  216 }
  217 
  218 SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
  219     0, 0, sysctl_kern_randompid, "I", "Random PID modulus");
  220 
  221 static int
  222 fork_findpid(int flags)
  223 {
  224         struct proc *p;
  225         int trypid;
  226         static int pidchecked = 0;
  227 
  228         /*
  229          * Requires allproc_lock in order to iterate over the list
  230          * of processes, and proctree_lock to access p_pgrp.
  231          */
  232         sx_assert(&allproc_lock, SX_LOCKED);
  233         sx_assert(&proctree_lock, SX_LOCKED);
  234 
  235         /*
  236          * Find an unused process ID.  We remember a range of unused IDs
  237          * ready to use (from lastpid+1 through pidchecked-1).
  238          *
  239          * If RFHIGHPID is set (used during system boot), do not allocate
  240          * low-numbered pids.
  241          */
  242         trypid = lastpid + 1;
  243         if (flags & RFHIGHPID) {
  244                 if (trypid < 10)
  245                         trypid = 10;
  246         } else {
  247                 if (randompid)
  248                         trypid += arc4random() % randompid;
  249         }
  250 retry:
  251         /*
  252          * If the process ID prototype has wrapped around,
  253          * restart somewhat above 0, as the low-numbered procs
  254          * tend to include daemons that don't exit.
  255          */
  256         if (trypid >= pid_max) {
  257                 trypid = trypid % pid_max;
  258                 if (trypid < 100)
  259                         trypid += 100;
  260                 pidchecked = 0;
  261         }
  262         if (trypid >= pidchecked) {
  263                 int doingzomb = 0;
  264 
  265                 pidchecked = PID_MAX;
  266                 /*
  267                  * Scan the active and zombie procs to check whether this pid
  268                  * is in use.  Remember the lowest pid that's greater
  269                  * than trypid, so we can avoid checking for a while.
  270                  *
  271                  * Avoid reuse of the process group id, session id or
  272                  * the reaper subtree id.  Note that for process group
  273                  * and sessions, the amount of reserved pids is
  274                  * limited by process limit.  For the subtree ids, the
  275                  * id is kept reserved only while there is a
  276                  * non-reaped process in the subtree, so amount of
  277                  * reserved pids is limited by process limit times
  278                  * two.
  279                  */
  280                 p = LIST_FIRST(&allproc);
  281 again:
  282                 for (; p != NULL; p = LIST_NEXT(p, p_list)) {
  283                         while (p->p_pid == trypid ||
  284                             p->p_reapsubtree == trypid ||
  285                             (p->p_pgrp != NULL &&
  286                             (p->p_pgrp->pg_id == trypid ||
  287                             (p->p_session != NULL &&
  288                             p->p_session->s_sid == trypid)))) {
  289                                 trypid++;
  290                                 if (trypid >= pidchecked)
  291                                         goto retry;
  292                         }
  293                         if (p->p_pid > trypid && pidchecked > p->p_pid)
  294                                 pidchecked = p->p_pid;
  295                         if (p->p_pgrp != NULL) {
  296                                 if (p->p_pgrp->pg_id > trypid &&
  297                                     pidchecked > p->p_pgrp->pg_id)
  298                                         pidchecked = p->p_pgrp->pg_id;
  299                                 if (p->p_session != NULL &&
  300                                     p->p_session->s_sid > trypid &&
  301                                     pidchecked > p->p_session->s_sid)
  302                                         pidchecked = p->p_session->s_sid;
  303                         }
  304                 }
  305                 if (!doingzomb) {
  306                         doingzomb = 1;
  307                         p = LIST_FIRST(&zombproc);
  308                         goto again;
  309                 }
  310         }
  311 
  312         /*
  313          * RFHIGHPID does not mess with the lastpid counter during boot.
  314          */
  315         if (flags & RFHIGHPID)
  316                 pidchecked = 0;
  317         else
  318                 lastpid = trypid;
  319 
  320         return (trypid);
  321 }
  322 
  323 static int
  324 fork_norfproc(struct thread *td, int flags)
  325 {
  326         int error;
  327         struct proc *p1;
  328 
  329         KASSERT((flags & RFPROC) == 0,
  330             ("fork_norfproc called with RFPROC set"));
  331         p1 = td->td_proc;
  332 
  333         if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
  334             (flags & (RFCFDG | RFFDG))) {
  335                 PROC_LOCK(p1);
  336                 if (thread_single(p1, SINGLE_BOUNDARY)) {
  337                         PROC_UNLOCK(p1);
  338                         return (ERESTART);
  339                 }
  340                 PROC_UNLOCK(p1);
  341         }
  342 
  343         error = vm_forkproc(td, NULL, NULL, NULL, flags);
  344         if (error)
  345                 goto fail;
  346 
  347         /*
  348          * Close all file descriptors.
  349          */
  350         if (flags & RFCFDG) {
  351                 struct filedesc *fdtmp;
  352                 fdtmp = fdinit(td->td_proc->p_fd);
  353                 fdescfree(td);
  354                 p1->p_fd = fdtmp;
  355         }
  356 
  357         /*
  358          * Unshare file descriptors (from parent).
  359          */
  360         if (flags & RFFDG)
  361                 fdunshare(td);
  362 
  363 fail:
  364         if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
  365             (flags & (RFCFDG | RFFDG))) {
  366                 PROC_LOCK(p1);
  367                 thread_single_end(p1, SINGLE_BOUNDARY);
  368                 PROC_UNLOCK(p1);
  369         }
  370         return (error);
  371 }
  372 
  373 static void
  374 do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
  375     struct vmspace *vm2, int pdflags)
  376 {
  377         struct proc *p1, *pptr;
  378         int p2_held, trypid;
  379         struct filedesc *fd;
  380         struct filedesc_to_leader *fdtol;
  381         struct sigacts *newsigacts;
  382 
  383         sx_assert(&proctree_lock, SX_SLOCKED);
  384         sx_assert(&allproc_lock, SX_XLOCKED);
  385 
  386         p2_held = 0;
  387         p1 = td->td_proc;
  388 
  389         trypid = fork_findpid(flags);
  390 
  391         sx_sunlock(&proctree_lock);
  392 
  393         p2->p_state = PRS_NEW;          /* protect against others */
  394         p2->p_pid = trypid;
  395         AUDIT_ARG_PID(p2->p_pid);
  396         LIST_INSERT_HEAD(&allproc, p2, p_list);
  397         allproc_gen++;
  398         LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
  399         tidhash_add(td2);
  400         PROC_LOCK(p2);
  401         PROC_LOCK(p1);
  402 
  403         sx_xunlock(&allproc_lock);
  404 
  405         bcopy(&p1->p_startcopy, &p2->p_startcopy,
  406             __rangeof(struct proc, p_startcopy, p_endcopy));
  407         p2->p_elf_machine = p1->p_elf_machine;
  408         p2->p_elf_flags = p1->p_elf_flags;
  409         pargs_hold(p2->p_args);
  410         PROC_UNLOCK(p1);
  411 
  412         bzero(&p2->p_startzero,
  413             __rangeof(struct proc, p_startzero, p_endzero));
  414         p2->p_treeflag = 0;
  415         p2->p_filemon = NULL;
  416         p2->p_ptevents = 0;
  417 
  418         /* Tell the prison that we exist. */
  419         prison_proc_hold(p2->p_ucred->cr_prison);
  420 
  421         PROC_UNLOCK(p2);
  422 
  423         /*
  424          * Malloc things while we don't hold any locks.
  425          */
  426         if (flags & RFSIGSHARE)
  427                 newsigacts = NULL;
  428         else
  429                 newsigacts = sigacts_alloc();
  430 
  431         /*
  432          * Copy filedesc.
  433          */
  434         if (flags & RFCFDG) {
  435                 fd = fdinit(p1->p_fd);
  436                 fdtol = NULL;
  437         } else if (flags & RFFDG) {
  438                 fd = fdcopy(p1->p_fd);
  439                 fdtol = NULL;
  440         } else {
  441                 fd = fdshare(p1->p_fd);
  442                 if (p1->p_fdtol == NULL)
  443                         p1->p_fdtol = filedesc_to_leader_alloc(NULL, NULL,
  444                             p1->p_leader);
  445                 if ((flags & RFTHREAD) != 0) {
  446                         /*
  447                          * Shared file descriptor table, and shared
  448                          * process leaders.
  449                          */
  450                         fdtol = p1->p_fdtol;
  451                         FILEDESC_XLOCK(p1->p_fd);
  452                         fdtol->fdl_refcount++;
  453                         FILEDESC_XUNLOCK(p1->p_fd);
  454                 } else {
  455                         /* 
  456                          * Shared file descriptor table, and different
  457                          * process leaders.
  458                          */
  459                         fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
  460                             p1->p_fd, p2);
  461                 }
  462         }
  463         /*
  464          * Make a proc table entry for the new process.
  465          * Start by zeroing the section of proc that is zero-initialized,
  466          * then copy the section that is copied directly from the parent.
  467          */
  468 
  469         PROC_LOCK(p2);
  470         PROC_LOCK(p1);
  471 
  472         bzero(&td2->td_startzero,
  473             __rangeof(struct thread, td_startzero, td_endzero));
  474         td2->td_su = NULL;
  475         td2->td_sleeptimo = 0;
  476 
  477         bcopy(&td->td_startcopy, &td2->td_startcopy,
  478             __rangeof(struct thread, td_startcopy, td_endcopy));
  479 
  480         bcopy(&p2->p_comm, &td2->td_name, sizeof(td2->td_name));
  481         td2->td_sigstk = td->td_sigstk;
  482         td2->td_flags = TDF_INMEM;
  483         td2->td_lend_user_pri = PRI_MAX;
  484         td2->td_dbg_sc_code = td->td_dbg_sc_code;
  485         td2->td_dbg_sc_narg = td->td_dbg_sc_narg;
  486 
  487 #ifdef VIMAGE
  488         td2->td_vnet = NULL;
  489         td2->td_vnet_lpush = NULL;
  490 #endif
  491 
  492         /*
  493          * Allow the scheduler to initialize the child.
  494          */
  495         thread_lock(td);
  496         sched_fork(td, td2);
  497         thread_unlock(td);
  498 
  499         /*
  500          * Duplicate sub-structures as needed.
  501          * Increase reference counts on shared objects.
  502          */
  503         p2->p_flag = P_INMEM;
  504         p2->p_flag2 = p1->p_flag2 & (P2_NOTRACE | P2_NOTRACE_EXEC);
  505         p2->p_swtick = ticks;
  506         if (p1->p_flag & P_PROFIL)
  507                 startprofclock(p2);
  508         td2->td_ucred = crhold(p2->p_ucred);
  509 
  510         if (flags & RFSIGSHARE) {
  511                 p2->p_sigacts = sigacts_hold(p1->p_sigacts);
  512         } else {
  513                 sigacts_copy(newsigacts, p1->p_sigacts);
  514                 p2->p_sigacts = newsigacts;
  515         }
  516 
  517         if (flags & RFTSIGZMB)
  518                 p2->p_sigparent = RFTSIGNUM(flags);
  519         else if (flags & RFLINUXTHPN)
  520                 p2->p_sigparent = SIGUSR1;
  521         else
  522                 p2->p_sigparent = SIGCHLD;
  523 
  524         p2->p_textvp = p1->p_textvp;
  525         p2->p_fd = fd;
  526         p2->p_fdtol = fdtol;
  527 
  528         if (p1->p_flag2 & P2_INHERIT_PROTECTED) {
  529                 p2->p_flag |= P_PROTECTED;
  530                 p2->p_flag2 |= P2_INHERIT_PROTECTED;
  531         }
  532 
  533         /*
  534          * p_limit is copy-on-write.  Bump its refcount.
  535          */
  536         lim_fork(p1, p2);
  537 
  538         pstats_fork(p1->p_stats, p2->p_stats);
  539 
  540         PROC_UNLOCK(p1);
  541         PROC_UNLOCK(p2);
  542 
  543         /* Bump references to the text vnode (for procfs). */
  544         if (p2->p_textvp)
  545                 vref(p2->p_textvp);
  546 
  547         /*
  548          * Set up linkage for kernel based threading.
  549          */
  550         if ((flags & RFTHREAD) != 0) {
  551                 mtx_lock(&ppeers_lock);
  552                 p2->p_peers = p1->p_peers;
  553                 p1->p_peers = p2;
  554                 p2->p_leader = p1->p_leader;
  555                 mtx_unlock(&ppeers_lock);
  556                 PROC_LOCK(p1->p_leader);
  557                 if ((p1->p_leader->p_flag & P_WEXIT) != 0) {
  558                         PROC_UNLOCK(p1->p_leader);
  559                         /*
  560                          * The task leader is exiting, so process p1 is
  561                          * going to be killed shortly.  Since p1 obviously
  562                          * isn't dead yet, we know that the leader is either
  563                          * sending SIGKILL's to all the processes in this
  564                          * task or is sleeping waiting for all the peers to
  565                          * exit.  We let p1 complete the fork, but we need
  566                          * to go ahead and kill the new process p2 since
  567                          * the task leader may not get a chance to send
  568                          * SIGKILL to it.  We leave it on the list so that
  569                          * the task leader will wait for this new process
  570                          * to commit suicide.
  571                          */
  572                         PROC_LOCK(p2);
  573                         kern_psignal(p2, SIGKILL);
  574                         PROC_UNLOCK(p2);
  575                 } else
  576                         PROC_UNLOCK(p1->p_leader);
  577         } else {
  578                 p2->p_peers = NULL;
  579                 p2->p_leader = p2;
  580         }
  581 
  582         sx_xlock(&proctree_lock);
  583         PGRP_LOCK(p1->p_pgrp);
  584         PROC_LOCK(p2);
  585         PROC_LOCK(p1);
  586 
  587         /*
  588          * Preserve some more flags in subprocess.  P_PROFIL has already
  589          * been preserved.
  590          */
  591         p2->p_flag |= p1->p_flag & P_SUGID;
  592         td2->td_pflags |= td->td_pflags & TDP_ALTSTACK;
  593         SESS_LOCK(p1->p_session);
  594         if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
  595                 p2->p_flag |= P_CONTROLT;
  596         SESS_UNLOCK(p1->p_session);
  597         if (flags & RFPPWAIT)
  598                 p2->p_flag |= P_PPWAIT;
  599 
  600         p2->p_pgrp = p1->p_pgrp;
  601         LIST_INSERT_AFTER(p1, p2, p_pglist);
  602         PGRP_UNLOCK(p1->p_pgrp);
  603         LIST_INIT(&p2->p_children);
  604         LIST_INIT(&p2->p_orphans);
  605 
  606         callout_init_mtx(&p2->p_itcallout, &p2->p_mtx, 0);
  607 
  608         /*
  609          * If PF_FORK is set, the child process inherits the
  610          * procfs ioctl flags from its parent.
  611          */
  612         if (p1->p_pfsflags & PF_FORK) {
  613                 p2->p_stops = p1->p_stops;
  614                 p2->p_pfsflags = p1->p_pfsflags;
  615         }
  616 
  617         /*
  618          * This begins the section where we must prevent the parent
  619          * from being swapped.
  620          */
  621         _PHOLD(p1);
  622         PROC_UNLOCK(p1);
  623 
  624         /*
  625          * Attach the new process to its parent.
  626          *
  627          * If RFNOWAIT is set, the newly created process becomes a child
  628          * of init.  This effectively disassociates the child from the
  629          * parent.
  630          */
  631         if ((flags & RFNOWAIT) != 0) {
  632                 pptr = p1->p_reaper;
  633                 p2->p_reaper = pptr;
  634         } else {
  635                 p2->p_reaper = (p1->p_treeflag & P_TREE_REAPER) != 0 ?
  636                     p1 : p1->p_reaper;
  637                 pptr = p1;
  638         }
  639         p2->p_pptr = pptr;
  640         LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
  641         LIST_INIT(&p2->p_reaplist);
  642         LIST_INSERT_HEAD(&p2->p_reaper->p_reaplist, p2, p_reapsibling);
  643         if (p2->p_reaper == p1)
  644                 p2->p_reapsubtree = p2->p_pid;
  645         else
  646                 p2->p_reapsubtree = p1->p_reapsubtree;          
  647         sx_xunlock(&proctree_lock);
  648 
  649         /* Inform accounting that we have forked. */
  650         p2->p_acflag = AFORK;
  651         PROC_UNLOCK(p2);
  652 
  653 #ifdef KTRACE
  654         ktrprocfork(p1, p2);
  655 #endif
  656 
  657         /*
  658          * Finish creating the child process.  It will return via a different
  659          * execution path later.  (ie: directly into user mode)
  660          */
  661         vm_forkproc(td, p2, td2, vm2, flags);
  662 
  663         if (flags == (RFFDG | RFPROC)) {
  664                 PCPU_INC(cnt.v_forks);
  665                 PCPU_ADD(cnt.v_forkpages, p2->p_vmspace->vm_dsize +
  666                     p2->p_vmspace->vm_ssize);
  667         } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
  668                 PCPU_INC(cnt.v_vforks);
  669                 PCPU_ADD(cnt.v_vforkpages, p2->p_vmspace->vm_dsize +
  670                     p2->p_vmspace->vm_ssize);
  671         } else if (p1 == &proc0) {
  672                 PCPU_INC(cnt.v_kthreads);
  673                 PCPU_ADD(cnt.v_kthreadpages, p2->p_vmspace->vm_dsize +
  674                     p2->p_vmspace->vm_ssize);
  675         } else {
  676                 PCPU_INC(cnt.v_rforks);
  677                 PCPU_ADD(cnt.v_rforkpages, p2->p_vmspace->vm_dsize +
  678                     p2->p_vmspace->vm_ssize);
  679         }
  680 
  681 #ifdef PROCDESC
  682         /*
  683          * Associate the process descriptor with the process before anything
  684          * can happen that might cause that process to need the descriptor.
  685          * However, don't do this until after fork(2) can no longer fail.
  686          */
  687         if (flags & RFPROCDESC)
  688                 procdesc_new(p2, pdflags);
  689 #endif
  690 
  691         /*
  692          * Both processes are set up, now check if any loadable modules want
  693          * to adjust anything.
  694          */
  695         EVENTHANDLER_INVOKE(process_fork, p1, p2, flags);
  696 
  697         /*
  698          * Set the child start time and mark the process as being complete.
  699          */
  700         PROC_LOCK(p2);
  701         PROC_LOCK(p1);
  702         microuptime(&p2->p_stats->p_start);
  703         PROC_SLOCK(p2);
  704         p2->p_state = PRS_NORMAL;
  705         PROC_SUNLOCK(p2);
  706 
  707 #ifdef KDTRACE_HOOKS
  708         /*
  709          * Tell the DTrace fasttrap provider about the new process so that any
  710          * tracepoints inherited from the parent can be removed. We have to do
  711          * this only after p_state is PRS_NORMAL since the fasttrap module will
  712          * use pfind() later on.
  713          */
  714         if ((flags & RFMEM) == 0 && dtrace_fasttrap_fork)
  715                 dtrace_fasttrap_fork(p1, p2);
  716 #endif
  717         if (p1->p_ptevents & PTRACE_FORK) {
  718                 /*
  719                  * Arrange for debugger to receive the fork event.
  720                  *
  721                  * We can report PL_FLAG_FORKED regardless of
  722                  * P_FOLLOWFORK settings, but it does not make a sense
  723                  * for runaway child.
  724                  */
  725                 td->td_dbgflags |= TDB_FORK;
  726                 td->td_dbg_forked = p2->p_pid;
  727                 td2->td_dbgflags |= TDB_STOPATFORK;
  728                 _PHOLD(p2);
  729                 p2_held = 1;
  730         }
  731         if (flags & RFPPWAIT) {
  732                 td->td_pflags |= TDP_RFPPWAIT;
  733                 td->td_rfppwait_p = p2;
  734                 td->td_dbgflags |= TDB_VFORK;
  735         }
  736         PROC_UNLOCK(p2);
  737         if ((flags & RFSTOPPED) == 0) {
  738                 /*
  739                  * If RFSTOPPED not requested, make child runnable and
  740                  * add to run queue.
  741                  */
  742                 thread_lock(td2);
  743                 TD_SET_CAN_RUN(td2);
  744                 sched_add(td2, SRQ_BORING);
  745                 thread_unlock(td2);
  746         }
  747 
  748         /*
  749          * Now can be swapped.
  750          */
  751         _PRELE(p1);
  752         PROC_UNLOCK(p1);
  753 
  754         /*
  755          * Tell any interested parties about the new process.
  756          */
  757         knote_fork(&p1->p_klist, p2->p_pid);
  758         SDT_PROBE3(proc, , , create, p2, p1, flags);
  759 
  760         /*
  761          * Wait until debugger is attached to child.
  762          */
  763         PROC_LOCK(p2);
  764         while ((td2->td_dbgflags & TDB_STOPATFORK) != 0)
  765                 cv_wait(&p2->p_dbgwait, &p2->p_mtx);
  766         if (p2_held)
  767                 _PRELE(p2);
  768         PROC_UNLOCK(p2);
  769 }
  770 
  771 int
  772 fork1(struct thread *td, int flags, int pages, struct proc **procp,
  773     int *procdescp, int pdflags)
  774 {
  775         struct proc *p1, *newproc;
  776         struct thread *td2;
  777         struct vmspace *vm2;
  778 #ifdef PROCDESC
  779         struct file *fp_procdesc;
  780 #endif
  781         vm_ooffset_t mem_charged;
  782         int error, nprocs_new, ok;
  783         static int curfail;
  784         static struct timeval lastfail;
  785 
  786         /* Check for the undefined or unimplemented flags. */
  787         if ((flags & ~(RFFLAGS | RFTSIGFLAGS(RFTSIGMASK))) != 0)
  788                 return (EINVAL);
  789 
  790         /* Signal value requires RFTSIGZMB. */
  791         if ((flags & RFTSIGFLAGS(RFTSIGMASK)) != 0 && (flags & RFTSIGZMB) == 0)
  792                 return (EINVAL);
  793 
  794         /* Can't copy and clear. */
  795         if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
  796                 return (EINVAL);
  797 
  798         /* Check the validity of the signal number. */
  799         if ((flags & RFTSIGZMB) != 0 && (u_int)RFTSIGNUM(flags) > _SIG_MAXSIG)
  800                 return (EINVAL);
  801 
  802 #ifdef PROCDESC
  803         if ((flags & RFPROCDESC) != 0) {
  804                 /* Can't not create a process yet get a process descriptor. */
  805                 if ((flags & RFPROC) == 0)
  806                         return (EINVAL);
  807 
  808                 /* Must provide a place to put a procdesc if creating one. */
  809                 if (procdescp == NULL)
  810                         return (EINVAL);
  811         }
  812 #endif
  813 
  814         p1 = td->td_proc;
  815 
  816         /*
  817          * Here we don't create a new process, but we divorce
  818          * certain parts of a process from itself.
  819          */
  820         if ((flags & RFPROC) == 0) {
  821                 *procp = NULL;
  822                 return (fork_norfproc(td, flags));
  823         }
  824 
  825 #ifdef PROCDESC
  826         fp_procdesc = NULL;
  827 #endif
  828         newproc = NULL;
  829         vm2 = NULL;
  830 
  831         /*
  832          * Increment the nprocs resource before allocations occur.
  833          * Although process entries are dynamically created, we still
  834          * keep a global limit on the maximum number we will
  835          * create. There are hard-limits as to the number of processes
  836          * that can run, established by the KVA and memory usage for
  837          * the process data.
  838          *
  839          * Don't allow a nonprivileged user to use the last ten
  840          * processes; don't let root exceed the limit.
  841          */
  842         nprocs_new = atomic_fetchadd_int(&nprocs, 1) + 1;
  843         if ((nprocs_new >= maxproc - 10 && priv_check_cred(td->td_ucred,
  844             PRIV_MAXPROC, 0) != 0) || nprocs_new >= maxproc) {
  845                 sx_xlock(&allproc_lock);
  846                 if (ppsratecheck(&lastfail, &curfail, 1)) {
  847                         printf("maxproc limit exceeded by uid %u (pid %d); "
  848                             "see tuning(7) and login.conf(5)\n",
  849                             td->td_ucred->cr_ruid, p1->p_pid);
  850                 }
  851                 sx_xunlock(&allproc_lock);
  852                 error = EAGAIN;
  853                 goto fail1;
  854         }
  855 
  856 #ifdef PROCDESC
  857         /*
  858          * If required, create a process descriptor in the parent first; we
  859          * will abandon it if something goes wrong. We don't finit() until
  860          * later.
  861          */
  862         if (flags & RFPROCDESC) {
  863                 error = falloc(td, &fp_procdesc, procdescp, 0);
  864                 if (error != 0)
  865                         goto fail1;
  866         }
  867 #endif
  868 
  869         mem_charged = 0;
  870         if (pages == 0)
  871                 pages = KSTACK_PAGES;
  872         /* Allocate new proc. */
  873         newproc = uma_zalloc(proc_zone, M_WAITOK);
  874         td2 = FIRST_THREAD_IN_PROC(newproc);
  875         if (td2 == NULL) {
  876                 td2 = thread_alloc(pages);
  877                 if (td2 == NULL) {
  878                         error = ENOMEM;
  879                         goto fail2;
  880                 }
  881                 proc_linkup(newproc, td2);
  882         } else {
  883                 if (td2->td_kstack == 0 || td2->td_kstack_pages != pages) {
  884                         if (td2->td_kstack != 0)
  885                                 vm_thread_dispose(td2);
  886                         if (!thread_alloc_stack(td2, pages)) {
  887                                 error = ENOMEM;
  888                                 goto fail2;
  889                         }
  890                 }
  891         }
  892 
  893         if ((flags & RFMEM) == 0) {
  894                 vm2 = vmspace_fork(p1->p_vmspace, &mem_charged);
  895                 if (vm2 == NULL) {
  896                         error = ENOMEM;
  897                         goto fail2;
  898                 }
  899                 if (!swap_reserve(mem_charged)) {
  900                         /*
  901                          * The swap reservation failed. The accounting
  902                          * from the entries of the copied vm2 will be
  903                          * subtracted in vmspace_free(), so force the
  904                          * reservation there.
  905                          */
  906                         swap_reserve_force(mem_charged);
  907                         error = ENOMEM;
  908                         goto fail2;
  909                 }
  910         } else
  911                 vm2 = NULL;
  912 
  913         /*
  914          * XXX: This is ugly; when we copy resource usage, we need to bump
  915          *      per-cred resource counters.
  916          */
  917         proc_set_cred_init(newproc, crhold(td->td_ucred));
  918 
  919         /*
  920          * Initialize resource accounting for the child process.
  921          */
  922         error = racct_proc_fork(p1, newproc);
  923         if (error != 0) {
  924                 error = EAGAIN;
  925                 goto fail1;
  926         }
  927 
  928 #ifdef MAC
  929         mac_proc_init(newproc);
  930 #endif
  931         knlist_init_mtx(&newproc->p_klist, &newproc->p_mtx);
  932         STAILQ_INIT(&newproc->p_ktr);
  933 
  934         /* We have to lock the process tree while we look for a pid. */
  935         sx_slock(&proctree_lock);
  936         sx_xlock(&allproc_lock);
  937 
  938         /*
  939          * Increment the count of procs running with this uid. Don't allow
  940          * a nonprivileged user to exceed their current limit.
  941          *
  942          * XXXRW: Can we avoid privilege here if it's not needed?
  943          */
  944         error = priv_check_cred(td->td_ucred, PRIV_PROC_LIMIT, 0);
  945         if (error == 0)
  946                 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1, 0);
  947         else {
  948                 PROC_LOCK(p1);
  949                 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1,
  950                     lim_cur(p1, RLIMIT_NPROC));
  951                 PROC_UNLOCK(p1);
  952         }
  953         if (ok) {
  954                 do_fork(td, flags, newproc, td2, vm2, pdflags);
  955 
  956                 /*
  957                  * Return child proc pointer to parent.
  958                  */
  959                 *procp = newproc;
  960 #ifdef PROCDESC
  961                 if (flags & RFPROCDESC) {
  962                         procdesc_finit(newproc->p_procdesc, fp_procdesc);
  963                         fdrop(fp_procdesc, td);
  964                 }
  965 #endif
  966                 racct_proc_fork_done(newproc);
  967                 return (0);
  968         }
  969 
  970         error = EAGAIN;
  971         sx_sunlock(&proctree_lock);
  972         sx_xunlock(&allproc_lock);
  973 #ifdef MAC
  974         mac_proc_destroy(newproc);
  975 #endif
  976         racct_proc_exit(newproc);
  977 fail1:
  978         crfree(newproc->p_ucred);
  979         newproc->p_ucred = NULL;
  980 fail2:
  981         if (vm2 != NULL)
  982                 vmspace_free(vm2);
  983         uma_zfree(proc_zone, newproc);
  984 #ifdef PROCDESC
  985         if ((flags & RFPROCDESC) != 0 && fp_procdesc != NULL) {
  986                 fdclose(td, fp_procdesc, *procdescp);
  987                 fdrop(fp_procdesc, td);
  988         }
  989 #endif
  990         atomic_add_int(&nprocs, -1);
  991         pause("fork", hz / 2);
  992         return (error);
  993 }
  994 
  995 /*
  996  * Handle the return of a child process from fork1().  This function
  997  * is called from the MD fork_trampoline() entry point.
  998  */
  999 void
 1000 fork_exit(void (*callout)(void *, struct trapframe *), void *arg,
 1001     struct trapframe *frame)
 1002 {
 1003         struct proc *p;
 1004         struct thread *td;
 1005         struct thread *dtd;
 1006 
 1007         td = curthread;
 1008         p = td->td_proc;
 1009         KASSERT(p->p_state == PRS_NORMAL, ("executing process is still new"));
 1010 
 1011         CTR4(KTR_PROC, "fork_exit: new thread %p (td_sched %p, pid %d, %s)",
 1012                 td, td->td_sched, p->p_pid, td->td_name);
 1013 
 1014         sched_fork_exit(td);
 1015         /*
 1016         * Processes normally resume in mi_switch() after being
 1017         * cpu_switch()'ed to, but when children start up they arrive here
 1018         * instead, so we must do much the same things as mi_switch() would.
 1019         */
 1020         if ((dtd = PCPU_GET(deadthread))) {
 1021                 PCPU_SET(deadthread, NULL);
 1022                 thread_stash(dtd);
 1023         }
 1024         thread_unlock(td);
 1025 
 1026         /*
 1027          * cpu_set_fork_handler intercepts this function call to
 1028          * have this call a non-return function to stay in kernel mode.
 1029          * initproc has its own fork handler, but it does return.
 1030          */
 1031         KASSERT(callout != NULL, ("NULL callout in fork_exit"));
 1032         callout(arg, frame);
 1033 
 1034         /*
 1035          * Check if a kernel thread misbehaved and returned from its main
 1036          * function.
 1037          */
 1038         if (p->p_flag & P_KTHREAD) {
 1039                 printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
 1040                     td->td_name, p->p_pid);
 1041                 kthread_exit();
 1042         }
 1043         mtx_assert(&Giant, MA_NOTOWNED);
 1044 
 1045         if (p->p_sysent->sv_schedtail != NULL)
 1046                 (p->p_sysent->sv_schedtail)(td);
 1047 }
 1048 
 1049 /*
 1050  * Simplified back end of syscall(), used when returning from fork()
 1051  * directly into user mode.  This function is passed in to fork_exit()
 1052  * as the first parameter and is called when returning to a new
 1053  * userland process.
 1054  */
 1055 void
 1056 fork_return(struct thread *td, struct trapframe *frame)
 1057 {
 1058         struct proc *p, *dbg;
 1059 
 1060         p = td->td_proc;
 1061         if (td->td_dbgflags & TDB_STOPATFORK) {
 1062                 sx_xlock(&proctree_lock);
 1063                 PROC_LOCK(p);
 1064                 if (p->p_pptr->p_ptevents & PTRACE_FORK) {
 1065                         /*
 1066                          * If debugger still wants auto-attach for the
 1067                          * parent's children, do it now.
 1068                          */
 1069                         dbg = p->p_pptr->p_pptr;
 1070                         proc_set_traced(p, true);
 1071                         CTR2(KTR_PTRACE,
 1072                     "fork_return: attaching to new child pid %d: oppid %d",
 1073                             p->p_pid, p->p_oppid);
 1074                         proc_reparent(p, dbg);
 1075                         sx_xunlock(&proctree_lock);
 1076                         td->td_dbgflags |= TDB_CHILD | TDB_SCX | TDB_FSTP;
 1077                         ptracestop(td, SIGSTOP, NULL);
 1078                         td->td_dbgflags &= ~(TDB_CHILD | TDB_SCX);
 1079                 } else {
 1080                         /*
 1081                          * ... otherwise clear the request.
 1082                          */
 1083                         sx_xunlock(&proctree_lock);
 1084                         td->td_dbgflags &= ~TDB_STOPATFORK;
 1085                         cv_broadcast(&p->p_dbgwait);
 1086                 }
 1087                 PROC_UNLOCK(p);
 1088         } else if (p->p_flag & P_TRACED || td->td_dbgflags & TDB_BORN) {
 1089                 /*
 1090                  * This is the start of a new thread in a traced
 1091                  * process.  Report a system call exit event.
 1092                  */
 1093                 PROC_LOCK(p);
 1094                 td->td_dbgflags |= TDB_SCX;
 1095                 _STOPEVENT(p, S_SCX, td->td_dbg_sc_code);
 1096                 if ((p->p_ptevents & PTRACE_SCX) != 0 ||
 1097                     (td->td_dbgflags & TDB_BORN) != 0)
 1098                         ptracestop(td, SIGTRAP, NULL);
 1099                 td->td_dbgflags &= ~(TDB_SCX | TDB_BORN);
 1100                 PROC_UNLOCK(p);
 1101         }
 1102 
 1103         userret(td, frame);
 1104 
 1105 #ifdef KTRACE
 1106         if (KTRPOINT(td, KTR_SYSRET))
 1107                 ktrsysret(SYS_fork, 0, 0);
 1108 #endif
 1109 }

Cache object: 7d899ad5b1eb122f654b9ea13e1a86f9


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