The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_fork.c

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    1 /*-
    2  * Copyright (c) 1982, 1986, 1989, 1991, 1993
    3  *      The Regents of the University of California.  All rights reserved.
    4  * (c) UNIX System Laboratories, Inc.
    5  * All or some portions of this file are derived from material licensed
    6  * to the University of California by American Telephone and Telegraph
    7  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
    8  * the permission of UNIX System Laboratories, Inc.
    9  *
   10  * Redistribution and use in source and binary forms, with or without
   11  * modification, are permitted provided that the following conditions
   12  * are met:
   13  * 1. Redistributions of source code must retain the above copyright
   14  *    notice, this list of conditions and the following disclaimer.
   15  * 2. Redistributions in binary form must reproduce the above copyright
   16  *    notice, this list of conditions and the following disclaimer in the
   17  *    documentation and/or other materials provided with the distribution.
   18  * 4. Neither the name of the University nor the names of its contributors
   19  *    may be used to endorse or promote products derived from this software
   20  *    without specific prior written permission.
   21  *
   22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   32  * SUCH DAMAGE.
   33  *
   34  *      @(#)kern_fork.c 8.6 (Berkeley) 4/8/94
   35  */
   36 
   37 #include <sys/cdefs.h>
   38 __FBSDID("$FreeBSD: releng/10.1/sys/kern/kern_fork.c 270267 2014-08-21 12:30:01Z kib $");
   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_DEFINE3(proc, kernel, , create, "struct proc *",
   93     "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                 p = LIST_FIRST(&allproc);
  272 again:
  273                 for (; p != NULL; p = LIST_NEXT(p, p_list)) {
  274                         while (p->p_pid == trypid ||
  275                             (p->p_pgrp != NULL &&
  276                             (p->p_pgrp->pg_id == trypid ||
  277                             (p->p_session != NULL &&
  278                             p->p_session->s_sid == trypid)))) {
  279                                 trypid++;
  280                                 if (trypid >= pidchecked)
  281                                         goto retry;
  282                         }
  283                         if (p->p_pid > trypid && pidchecked > p->p_pid)
  284                                 pidchecked = p->p_pid;
  285                         if (p->p_pgrp != NULL) {
  286                                 if (p->p_pgrp->pg_id > trypid &&
  287                                     pidchecked > p->p_pgrp->pg_id)
  288                                         pidchecked = p->p_pgrp->pg_id;
  289                                 if (p->p_session != NULL &&
  290                                     p->p_session->s_sid > trypid &&
  291                                     pidchecked > p->p_session->s_sid)
  292                                         pidchecked = p->p_session->s_sid;
  293                         }
  294                 }
  295                 if (!doingzomb) {
  296                         doingzomb = 1;
  297                         p = LIST_FIRST(&zombproc);
  298                         goto again;
  299                 }
  300         }
  301 
  302         /*
  303          * RFHIGHPID does not mess with the lastpid counter during boot.
  304          */
  305         if (flags & RFHIGHPID)
  306                 pidchecked = 0;
  307         else
  308                 lastpid = trypid;
  309 
  310         return (trypid);
  311 }
  312 
  313 static int
  314 fork_norfproc(struct thread *td, int flags)
  315 {
  316         int error;
  317         struct proc *p1;
  318 
  319         KASSERT((flags & RFPROC) == 0,
  320             ("fork_norfproc called with RFPROC set"));
  321         p1 = td->td_proc;
  322 
  323         if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
  324             (flags & (RFCFDG | RFFDG))) {
  325                 PROC_LOCK(p1);
  326                 if (thread_single(SINGLE_BOUNDARY)) {
  327                         PROC_UNLOCK(p1);
  328                         return (ERESTART);
  329                 }
  330                 PROC_UNLOCK(p1);
  331         }
  332 
  333         error = vm_forkproc(td, NULL, NULL, NULL, flags);
  334         if (error)
  335                 goto fail;
  336 
  337         /*
  338          * Close all file descriptors.
  339          */
  340         if (flags & RFCFDG) {
  341                 struct filedesc *fdtmp;
  342                 fdtmp = fdinit(td->td_proc->p_fd);
  343                 fdescfree(td);
  344                 p1->p_fd = fdtmp;
  345         }
  346 
  347         /*
  348          * Unshare file descriptors (from parent).
  349          */
  350         if (flags & RFFDG)
  351                 fdunshare(td);
  352 
  353 fail:
  354         if (((p1->p_flag & (P_HADTHREADS|P_SYSTEM)) == P_HADTHREADS) &&
  355             (flags & (RFCFDG | RFFDG))) {
  356                 PROC_LOCK(p1);
  357                 thread_single_end();
  358                 PROC_UNLOCK(p1);
  359         }
  360         return (error);
  361 }
  362 
  363 static void
  364 do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
  365     struct vmspace *vm2, int pdflags)
  366 {
  367         struct proc *p1, *pptr;
  368         int p2_held, trypid;
  369         struct filedesc *fd;
  370         struct filedesc_to_leader *fdtol;
  371         struct sigacts *newsigacts;
  372 
  373         sx_assert(&proctree_lock, SX_SLOCKED);
  374         sx_assert(&allproc_lock, SX_XLOCKED);
  375 
  376         p2_held = 0;
  377         p1 = td->td_proc;
  378 
  379         /*
  380          * Increment the nprocs resource before blocking can occur.  There
  381          * are hard-limits as to the number of processes that can run.
  382          */
  383         nprocs++;
  384 
  385         trypid = fork_findpid(flags);
  386 
  387         sx_sunlock(&proctree_lock);
  388 
  389         p2->p_state = PRS_NEW;          /* protect against others */
  390         p2->p_pid = trypid;
  391         AUDIT_ARG_PID(p2->p_pid);
  392         LIST_INSERT_HEAD(&allproc, p2, p_list);
  393         LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
  394         tidhash_add(td2);
  395         PROC_LOCK(p2);
  396         PROC_LOCK(p1);
  397 
  398         sx_xunlock(&allproc_lock);
  399 
  400         bcopy(&p1->p_startcopy, &p2->p_startcopy,
  401             __rangeof(struct proc, p_startcopy, p_endcopy));
  402         pargs_hold(p2->p_args);
  403         PROC_UNLOCK(p1);
  404 
  405         bzero(&p2->p_startzero,
  406             __rangeof(struct proc, p_startzero, p_endzero));
  407         p2->p_treeflag = 0;
  408 
  409         p2->p_ucred = crhold(td->td_ucred);
  410 
  411         /* Tell the prison that we exist. */
  412         prison_proc_hold(p2->p_ucred->cr_prison);
  413 
  414         PROC_UNLOCK(p2);
  415 
  416         /*
  417          * Malloc things while we don't hold any locks.
  418          */
  419         if (flags & RFSIGSHARE)
  420                 newsigacts = NULL;
  421         else
  422                 newsigacts = sigacts_alloc();
  423 
  424         /*
  425          * Copy filedesc.
  426          */
  427         if (flags & RFCFDG) {
  428                 fd = fdinit(p1->p_fd);
  429                 fdtol = NULL;
  430         } else if (flags & RFFDG) {
  431                 fd = fdcopy(p1->p_fd);
  432                 fdtol = NULL;
  433         } else {
  434                 fd = fdshare(p1->p_fd);
  435                 if (p1->p_fdtol == NULL)
  436                         p1->p_fdtol = filedesc_to_leader_alloc(NULL, NULL,
  437                             p1->p_leader);
  438                 if ((flags & RFTHREAD) != 0) {
  439                         /*
  440                          * Shared file descriptor table, and shared
  441                          * process leaders.
  442                          */
  443                         fdtol = p1->p_fdtol;
  444                         FILEDESC_XLOCK(p1->p_fd);
  445                         fdtol->fdl_refcount++;
  446                         FILEDESC_XUNLOCK(p1->p_fd);
  447                 } else {
  448                         /* 
  449                          * Shared file descriptor table, and different
  450                          * process leaders.
  451                          */
  452                         fdtol = filedesc_to_leader_alloc(p1->p_fdtol,
  453                             p1->p_fd, p2);
  454                 }
  455         }
  456         /*
  457          * Make a proc table entry for the new process.
  458          * Start by zeroing the section of proc that is zero-initialized,
  459          * then copy the section that is copied directly from the parent.
  460          */
  461 
  462         PROC_LOCK(p2);
  463         PROC_LOCK(p1);
  464 
  465         bzero(&td2->td_startzero,
  466             __rangeof(struct thread, td_startzero, td_endzero));
  467 
  468         bcopy(&td->td_startcopy, &td2->td_startcopy,
  469             __rangeof(struct thread, td_startcopy, td_endcopy));
  470 
  471         bcopy(&p2->p_comm, &td2->td_name, sizeof(td2->td_name));
  472         td2->td_sigstk = td->td_sigstk;
  473         td2->td_flags = TDF_INMEM;
  474         td2->td_lend_user_pri = PRI_MAX;
  475 
  476 #ifdef VIMAGE
  477         td2->td_vnet = NULL;
  478         td2->td_vnet_lpush = NULL;
  479 #endif
  480 
  481         /*
  482          * Allow the scheduler to initialize the child.
  483          */
  484         thread_lock(td);
  485         sched_fork(td, td2);
  486         thread_unlock(td);
  487 
  488         /*
  489          * Duplicate sub-structures as needed.
  490          * Increase reference counts on shared objects.
  491          */
  492         p2->p_flag = P_INMEM;
  493         p2->p_flag2 = 0;
  494         p2->p_swtick = ticks;
  495         if (p1->p_flag & P_PROFIL)
  496                 startprofclock(p2);
  497         td2->td_ucred = crhold(p2->p_ucred);
  498 
  499         if (flags & RFSIGSHARE) {
  500                 p2->p_sigacts = sigacts_hold(p1->p_sigacts);
  501         } else {
  502                 sigacts_copy(newsigacts, p1->p_sigacts);
  503                 p2->p_sigacts = newsigacts;
  504         }
  505 
  506         if (flags & RFTSIGZMB)
  507                 p2->p_sigparent = RFTSIGNUM(flags);
  508         else if (flags & RFLINUXTHPN)
  509                 p2->p_sigparent = SIGUSR1;
  510         else
  511                 p2->p_sigparent = SIGCHLD;
  512 
  513         p2->p_textvp = p1->p_textvp;
  514         p2->p_fd = fd;
  515         p2->p_fdtol = fdtol;
  516 
  517         if (p1->p_flag2 & P2_INHERIT_PROTECTED) {
  518                 p2->p_flag |= P_PROTECTED;
  519                 p2->p_flag2 |= P2_INHERIT_PROTECTED;
  520         }
  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         LIST_INIT(&p2->p_orphans);
  594 
  595         callout_init_mtx(&p2->p_itcallout, &p2->p_mtx, 0);
  596 
  597         /*
  598          * If PF_FORK is set, the child process inherits the
  599          * procfs ioctl flags from its parent.
  600          */
  601         if (p1->p_pfsflags & PF_FORK) {
  602                 p2->p_stops = p1->p_stops;
  603                 p2->p_pfsflags = p1->p_pfsflags;
  604         }
  605 
  606         /*
  607          * This begins the section where we must prevent the parent
  608          * from being swapped.
  609          */
  610         _PHOLD(p1);
  611         PROC_UNLOCK(p1);
  612 
  613         /*
  614          * Attach the new process to its parent.
  615          *
  616          * If RFNOWAIT is set, the newly created process becomes a child
  617          * of init.  This effectively disassociates the child from the
  618          * parent.
  619          */
  620         if (flags & RFNOWAIT)
  621                 pptr = initproc;
  622         else
  623                 pptr = p1;
  624         p2->p_pptr = pptr;
  625         LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
  626         sx_xunlock(&proctree_lock);
  627 
  628         /* Inform accounting that we have forked. */
  629         p2->p_acflag = AFORK;
  630         PROC_UNLOCK(p2);
  631 
  632 #ifdef KTRACE
  633         ktrprocfork(p1, p2);
  634 #endif
  635 
  636         /*
  637          * Finish creating the child process.  It will return via a different
  638          * execution path later.  (ie: directly into user mode)
  639          */
  640         vm_forkproc(td, p2, td2, vm2, flags);
  641 
  642         if (flags == (RFFDG | RFPROC)) {
  643                 PCPU_INC(cnt.v_forks);
  644                 PCPU_ADD(cnt.v_forkpages, p2->p_vmspace->vm_dsize +
  645                     p2->p_vmspace->vm_ssize);
  646         } else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
  647                 PCPU_INC(cnt.v_vforks);
  648                 PCPU_ADD(cnt.v_vforkpages, p2->p_vmspace->vm_dsize +
  649                     p2->p_vmspace->vm_ssize);
  650         } else if (p1 == &proc0) {
  651                 PCPU_INC(cnt.v_kthreads);
  652                 PCPU_ADD(cnt.v_kthreadpages, p2->p_vmspace->vm_dsize +
  653                     p2->p_vmspace->vm_ssize);
  654         } else {
  655                 PCPU_INC(cnt.v_rforks);
  656                 PCPU_ADD(cnt.v_rforkpages, p2->p_vmspace->vm_dsize +
  657                     p2->p_vmspace->vm_ssize);
  658         }
  659 
  660 #ifdef PROCDESC
  661         /*
  662          * Associate the process descriptor with the process before anything
  663          * can happen that might cause that process to need the descriptor.
  664          * However, don't do this until after fork(2) can no longer fail.
  665          */
  666         if (flags & RFPROCDESC)
  667                 procdesc_new(p2, pdflags);
  668 #endif
  669 
  670         /*
  671          * Both processes are set up, now check if any loadable modules want
  672          * to adjust anything.
  673          */
  674         EVENTHANDLER_INVOKE(process_fork, p1, p2, flags);
  675 
  676         /*
  677          * Set the child start time and mark the process as being complete.
  678          */
  679         PROC_LOCK(p2);
  680         PROC_LOCK(p1);
  681         microuptime(&p2->p_stats->p_start);
  682         PROC_SLOCK(p2);
  683         p2->p_state = PRS_NORMAL;
  684         PROC_SUNLOCK(p2);
  685 
  686 #ifdef KDTRACE_HOOKS
  687         /*
  688          * Tell the DTrace fasttrap provider about the new process so that any
  689          * tracepoints inherited from the parent can be removed. We have to do
  690          * this only after p_state is PRS_NORMAL since the fasttrap module will
  691          * use pfind() later on.
  692          */
  693         if ((flags & RFMEM) == 0 && dtrace_fasttrap_fork)
  694                 dtrace_fasttrap_fork(p1, p2);
  695 #endif
  696         if ((p1->p_flag & (P_TRACED | P_FOLLOWFORK)) == (P_TRACED |
  697             P_FOLLOWFORK)) {
  698                 /*
  699                  * Arrange for debugger to receive the fork event.
  700                  *
  701                  * We can report PL_FLAG_FORKED regardless of
  702                  * P_FOLLOWFORK settings, but it does not make a sense
  703                  * for runaway child.
  704                  */
  705                 td->td_dbgflags |= TDB_FORK;
  706                 td->td_dbg_forked = p2->p_pid;
  707                 td2->td_dbgflags |= TDB_STOPATFORK;
  708                 _PHOLD(p2);
  709                 p2_held = 1;
  710         }
  711         if (flags & RFPPWAIT) {
  712                 td->td_pflags |= TDP_RFPPWAIT;
  713                 td->td_rfppwait_p = p2;
  714         }
  715         PROC_UNLOCK(p2);
  716         if ((flags & RFSTOPPED) == 0) {
  717                 /*
  718                  * If RFSTOPPED not requested, make child runnable and
  719                  * add to run queue.
  720                  */
  721                 thread_lock(td2);
  722                 TD_SET_CAN_RUN(td2);
  723                 sched_add(td2, SRQ_BORING);
  724                 thread_unlock(td2);
  725         }
  726 
  727         /*
  728          * Now can be swapped.
  729          */
  730         _PRELE(p1);
  731         PROC_UNLOCK(p1);
  732 
  733         /*
  734          * Tell any interested parties about the new process.
  735          */
  736         knote_fork(&p1->p_klist, p2->p_pid);
  737         SDT_PROBE(proc, kernel, , create, p2, p1, flags, 0, 0);
  738 
  739         /*
  740          * Wait until debugger is attached to child.
  741          */
  742         PROC_LOCK(p2);
  743         while ((td2->td_dbgflags & TDB_STOPATFORK) != 0)
  744                 cv_wait(&p2->p_dbgwait, &p2->p_mtx);
  745         if (p2_held)
  746                 _PRELE(p2);
  747         PROC_UNLOCK(p2);
  748 }
  749 
  750 int
  751 fork1(struct thread *td, int flags, int pages, struct proc **procp,
  752     int *procdescp, int pdflags)
  753 {
  754         struct proc *p1;
  755         struct proc *newproc;
  756         int ok;
  757         struct thread *td2;
  758         struct vmspace *vm2;
  759         vm_ooffset_t mem_charged;
  760         int error;
  761         static int curfail;
  762         static struct timeval lastfail;
  763 #ifdef PROCDESC
  764         struct file *fp_procdesc = NULL;
  765 #endif
  766 
  767         /* Check for the undefined or unimplemented flags. */
  768         if ((flags & ~(RFFLAGS | RFTSIGFLAGS(RFTSIGMASK))) != 0)
  769                 return (EINVAL);
  770 
  771         /* Signal value requires RFTSIGZMB. */
  772         if ((flags & RFTSIGFLAGS(RFTSIGMASK)) != 0 && (flags & RFTSIGZMB) == 0)
  773                 return (EINVAL);
  774 
  775         /* Can't copy and clear. */
  776         if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
  777                 return (EINVAL);
  778 
  779         /* Check the validity of the signal number. */
  780         if ((flags & RFTSIGZMB) != 0 && (u_int)RFTSIGNUM(flags) > _SIG_MAXSIG)
  781                 return (EINVAL);
  782 
  783 #ifdef PROCDESC
  784         if ((flags & RFPROCDESC) != 0) {
  785                 /* Can't not create a process yet get a process descriptor. */
  786                 if ((flags & RFPROC) == 0)
  787                         return (EINVAL);
  788 
  789                 /* Must provide a place to put a procdesc if creating one. */
  790                 if (procdescp == NULL)
  791                         return (EINVAL);
  792         }
  793 #endif
  794 
  795         p1 = td->td_proc;
  796 
  797         /*
  798          * Here we don't create a new process, but we divorce
  799          * certain parts of a process from itself.
  800          */
  801         if ((flags & RFPROC) == 0) {
  802                 *procp = NULL;
  803                 return (fork_norfproc(td, flags));
  804         }
  805 
  806 #ifdef PROCDESC
  807         /*
  808          * If required, create a process descriptor in the parent first; we
  809          * will abandon it if something goes wrong. We don't finit() until
  810          * later.
  811          */
  812         if (flags & RFPROCDESC) {
  813                 error = falloc(td, &fp_procdesc, procdescp, 0);
  814                 if (error != 0)
  815                         return (error);
  816         }
  817 #endif
  818 
  819         mem_charged = 0;
  820         vm2 = NULL;
  821         if (pages == 0)
  822                 pages = KSTACK_PAGES;
  823         /* Allocate new proc. */
  824         newproc = uma_zalloc(proc_zone, M_WAITOK);
  825         td2 = FIRST_THREAD_IN_PROC(newproc);
  826         if (td2 == NULL) {
  827                 td2 = thread_alloc(pages);
  828                 if (td2 == NULL) {
  829                         error = ENOMEM;
  830                         goto fail1;
  831                 }
  832                 proc_linkup(newproc, td2);
  833         } else {
  834                 if (td2->td_kstack == 0 || td2->td_kstack_pages != pages) {
  835                         if (td2->td_kstack != 0)
  836                                 vm_thread_dispose(td2);
  837                         if (!thread_alloc_stack(td2, pages)) {
  838                                 error = ENOMEM;
  839                                 goto fail1;
  840                         }
  841                 }
  842         }
  843 
  844         if ((flags & RFMEM) == 0) {
  845                 vm2 = vmspace_fork(p1->p_vmspace, &mem_charged);
  846                 if (vm2 == NULL) {
  847                         error = ENOMEM;
  848                         goto fail1;
  849                 }
  850                 if (!swap_reserve(mem_charged)) {
  851                         /*
  852                          * The swap reservation failed. The accounting
  853                          * from the entries of the copied vm2 will be
  854                          * substracted in vmspace_free(), so force the
  855                          * reservation there.
  856                          */
  857                         swap_reserve_force(mem_charged);
  858                         error = ENOMEM;
  859                         goto fail1;
  860                 }
  861         } else
  862                 vm2 = NULL;
  863 
  864         /*
  865          * XXX: This is ugly; when we copy resource usage, we need to bump
  866          *      per-cred resource counters.
  867          */
  868         newproc->p_ucred = p1->p_ucred;
  869 
  870         /*
  871          * Initialize resource accounting for the child process.
  872          */
  873         error = racct_proc_fork(p1, newproc);
  874         if (error != 0) {
  875                 error = EAGAIN;
  876                 goto fail1;
  877         }
  878 
  879 #ifdef MAC
  880         mac_proc_init(newproc);
  881 #endif
  882         knlist_init_mtx(&newproc->p_klist, &newproc->p_mtx);
  883         STAILQ_INIT(&newproc->p_ktr);
  884 
  885         /* We have to lock the process tree while we look for a pid. */
  886         sx_slock(&proctree_lock);
  887 
  888         /*
  889          * Although process entries are dynamically created, we still keep
  890          * a global limit on the maximum number we will create.  Don't allow
  891          * a nonprivileged user to use the last ten processes; don't let root
  892          * exceed the limit. The variable nprocs is the current number of
  893          * processes, maxproc is the limit.
  894          */
  895         sx_xlock(&allproc_lock);
  896         if ((nprocs >= maxproc - 10 && priv_check_cred(td->td_ucred,
  897             PRIV_MAXPROC, 0) != 0) || nprocs >= maxproc) {
  898                 error = EAGAIN;
  899                 goto fail;
  900         }
  901 
  902         /*
  903          * Increment the count of procs running with this uid. Don't allow
  904          * a nonprivileged user to exceed their current limit.
  905          *
  906          * XXXRW: Can we avoid privilege here if it's not needed?
  907          */
  908         error = priv_check_cred(td->td_ucred, PRIV_PROC_LIMIT, 0);
  909         if (error == 0)
  910                 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1, 0);
  911         else {
  912                 PROC_LOCK(p1);
  913                 ok = chgproccnt(td->td_ucred->cr_ruidinfo, 1,
  914                     lim_cur(p1, RLIMIT_NPROC));
  915                 PROC_UNLOCK(p1);
  916         }
  917         if (ok) {
  918                 do_fork(td, flags, newproc, td2, vm2, pdflags);
  919 
  920                 /*
  921                  * Return child proc pointer to parent.
  922                  */
  923                 *procp = newproc;
  924 #ifdef PROCDESC
  925                 if (flags & RFPROCDESC) {
  926                         procdesc_finit(newproc->p_procdesc, fp_procdesc);
  927                         fdrop(fp_procdesc, td);
  928                 }
  929 #endif
  930                 racct_proc_fork_done(newproc);
  931                 return (0);
  932         }
  933 
  934         error = EAGAIN;
  935 fail:
  936         sx_sunlock(&proctree_lock);
  937         if (ppsratecheck(&lastfail, &curfail, 1))
  938                 printf("maxproc limit exceeded by uid %u (pid %d); see tuning(7) and login.conf(5)\n",
  939                     td->td_ucred->cr_ruid, p1->p_pid);
  940         sx_xunlock(&allproc_lock);
  941 #ifdef MAC
  942         mac_proc_destroy(newproc);
  943 #endif
  944         racct_proc_exit(newproc);
  945 fail1:
  946         if (vm2 != NULL)
  947                 vmspace_free(vm2);
  948         uma_zfree(proc_zone, newproc);
  949 #ifdef PROCDESC
  950         if ((flags & RFPROCDESC) != 0 && fp_procdesc != NULL) {
  951                 fdclose(td->td_proc->p_fd, fp_procdesc, *procdescp, td);
  952                 fdrop(fp_procdesc, td);
  953         }
  954 #endif
  955         pause("fork", hz / 2);
  956         return (error);
  957 }
  958 
  959 /*
  960  * Handle the return of a child process from fork1().  This function
  961  * is called from the MD fork_trampoline() entry point.
  962  */
  963 void
  964 fork_exit(void (*callout)(void *, struct trapframe *), void *arg,
  965     struct trapframe *frame)
  966 {
  967         struct proc *p;
  968         struct thread *td;
  969         struct thread *dtd;
  970 
  971         td = curthread;
  972         p = td->td_proc;
  973         KASSERT(p->p_state == PRS_NORMAL, ("executing process is still new"));
  974 
  975         CTR4(KTR_PROC, "fork_exit: new thread %p (td_sched %p, pid %d, %s)",
  976                 td, td->td_sched, p->p_pid, td->td_name);
  977 
  978         sched_fork_exit(td);
  979         /*
  980         * Processes normally resume in mi_switch() after being
  981         * cpu_switch()'ed to, but when children start up they arrive here
  982         * instead, so we must do much the same things as mi_switch() would.
  983         */
  984         if ((dtd = PCPU_GET(deadthread))) {
  985                 PCPU_SET(deadthread, NULL);
  986                 thread_stash(dtd);
  987         }
  988         thread_unlock(td);
  989 
  990         /*
  991          * cpu_set_fork_handler intercepts this function call to
  992          * have this call a non-return function to stay in kernel mode.
  993          * initproc has its own fork handler, but it does return.
  994          */
  995         KASSERT(callout != NULL, ("NULL callout in fork_exit"));
  996         callout(arg, frame);
  997 
  998         /*
  999          * Check if a kernel thread misbehaved and returned from its main
 1000          * function.
 1001          */
 1002         if (p->p_flag & P_KTHREAD) {
 1003                 printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
 1004                     td->td_name, p->p_pid);
 1005                 kproc_exit(0);
 1006         }
 1007         mtx_assert(&Giant, MA_NOTOWNED);
 1008 
 1009         if (p->p_sysent->sv_schedtail != NULL)
 1010                 (p->p_sysent->sv_schedtail)(td);
 1011 }
 1012 
 1013 /*
 1014  * Simplified back end of syscall(), used when returning from fork()
 1015  * directly into user mode.  Giant is not held on entry, and must not
 1016  * be held on return.  This function is passed in to fork_exit() as the
 1017  * first parameter and is called when returning to a new userland process.
 1018  */
 1019 void
 1020 fork_return(struct thread *td, struct trapframe *frame)
 1021 {
 1022         struct proc *p, *dbg;
 1023 
 1024         if (td->td_dbgflags & TDB_STOPATFORK) {
 1025                 p = td->td_proc;
 1026                 sx_xlock(&proctree_lock);
 1027                 PROC_LOCK(p);
 1028                 if ((p->p_pptr->p_flag & (P_TRACED | P_FOLLOWFORK)) ==
 1029                     (P_TRACED | P_FOLLOWFORK)) {
 1030                         /*
 1031                          * If debugger still wants auto-attach for the
 1032                          * parent's children, do it now.
 1033                          */
 1034                         dbg = p->p_pptr->p_pptr;
 1035                         p->p_flag |= P_TRACED;
 1036                         p->p_oppid = p->p_pptr->p_pid;
 1037                         proc_reparent(p, dbg);
 1038                         sx_xunlock(&proctree_lock);
 1039                         td->td_dbgflags |= TDB_CHILD;
 1040                         ptracestop(td, SIGSTOP);
 1041                         td->td_dbgflags &= ~TDB_CHILD;
 1042                 } else {
 1043                         /*
 1044                          * ... otherwise clear the request.
 1045                          */
 1046                         sx_xunlock(&proctree_lock);
 1047                         td->td_dbgflags &= ~TDB_STOPATFORK;
 1048                         cv_broadcast(&p->p_dbgwait);
 1049                 }
 1050                 PROC_UNLOCK(p);
 1051         }
 1052 
 1053         userret(td, frame);
 1054 
 1055 #ifdef KTRACE
 1056         if (KTRPOINT(td, KTR_SYSRET))
 1057                 ktrsysret(SYS_fork, 0, 0);
 1058 #endif
 1059 }

Cache object: af332250917e8f4c47230f5943deffe6


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