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 /*      $NetBSD: kern_fork.c,v 1.121.2.2 2005/05/23 19:09:56 riz Exp $  */
    2 
    3 /*-
    4  * Copyright (c) 1999, 2001, 2004 The NetBSD Foundation, Inc.
    5  * All rights reserved.
    6  *
    7  * This code is derived from software contributed to The NetBSD Foundation
    8  * by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
    9  * NASA Ames Research Center.
   10  * This code is derived from software contributed to The NetBSD Foundation
   11  * by Charles M. Hannum.
   12  *
   13  * Redistribution and use in source and binary forms, with or without
   14  * modification, are permitted provided that the following conditions
   15  * are met:
   16  * 1. Redistributions of source code must retain the above copyright
   17  *    notice, this list of conditions and the following disclaimer.
   18  * 2. Redistributions in binary form must reproduce the above copyright
   19  *    notice, this list of conditions and the following disclaimer in the
   20  *    documentation and/or other materials provided with the distribution.
   21  * 3. All advertising materials mentioning features or use of this software
   22  *    must display the following acknowledgement:
   23  *      This product includes software developed by the NetBSD
   24  *      Foundation, Inc. and its contributors.
   25  * 4. Neither the name of The NetBSD Foundation nor the names of its
   26  *    contributors may be used to endorse or promote products derived
   27  *    from this software without specific prior written permission.
   28  *
   29  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
   30  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   31  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   32  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
   33  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   34  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   35  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   36  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   37  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   38  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   39  * POSSIBILITY OF SUCH DAMAGE.
   40  */
   41 
   42 /*
   43  * Copyright (c) 1982, 1986, 1989, 1991, 1993
   44  *      The Regents of the University of California.  All rights reserved.
   45  * (c) UNIX System Laboratories, Inc.
   46  * All or some portions of this file are derived from material licensed
   47  * to the University of California by American Telephone and Telegraph
   48  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
   49  * the permission of UNIX System Laboratories, Inc.
   50  *
   51  * Redistribution and use in source and binary forms, with or without
   52  * modification, are permitted provided that the following conditions
   53  * are met:
   54  * 1. Redistributions of source code must retain the above copyright
   55  *    notice, this list of conditions and the following disclaimer.
   56  * 2. Redistributions in binary form must reproduce the above copyright
   57  *    notice, this list of conditions and the following disclaimer in the
   58  *    documentation and/or other materials provided with the distribution.
   59  * 3. Neither the name of the University nor the names of its contributors
   60  *    may be used to endorse or promote products derived from this software
   61  *    without specific prior written permission.
   62  *
   63  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   64  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   65  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   66  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   67  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   68  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   69  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   70  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   71  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   72  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   73  * SUCH DAMAGE.
   74  *
   75  *      @(#)kern_fork.c 8.8 (Berkeley) 2/14/95
   76  */
   77 
   78 #include <sys/cdefs.h>
   79 __KERNEL_RCSID(0, "$NetBSD: kern_fork.c,v 1.121.2.2 2005/05/23 19:09:56 riz Exp $");
   80 
   81 #include "opt_ktrace.h"
   82 #include "opt_systrace.h"
   83 #include "opt_multiprocessor.h"
   84 
   85 #include <sys/param.h>
   86 #include <sys/systm.h>
   87 #include <sys/filedesc.h>
   88 #include <sys/kernel.h>
   89 #include <sys/malloc.h>
   90 #include <sys/pool.h>
   91 #include <sys/mount.h>
   92 #include <sys/proc.h>
   93 #include <sys/ras.h>
   94 #include <sys/resourcevar.h>
   95 #include <sys/vnode.h>
   96 #include <sys/file.h>
   97 #include <sys/acct.h>
   98 #include <sys/ktrace.h>
   99 #include <sys/vmmeter.h>
  100 #include <sys/sched.h>
  101 #include <sys/signalvar.h>
  102 #include <sys/systrace.h>
  103 
  104 #include <sys/sa.h>
  105 #include <sys/syscallargs.h>
  106 
  107 #include <uvm/uvm_extern.h>
  108 
  109 
  110 int     nprocs = 1;             /* process 0 */
  111 
  112 /*
  113  * Number of ticks to sleep if fork() would fail due to process hitting
  114  * limits. Exported in miliseconds to userland via sysctl.
  115  */
  116 int     forkfsleep = 0;
  117 
  118 /*ARGSUSED*/
  119 int
  120 sys_fork(struct lwp *l, void *v, register_t *retval)
  121 {
  122 
  123         return (fork1(l, 0, SIGCHLD, NULL, 0, NULL, NULL, retval, NULL));
  124 }
  125 
  126 /*
  127  * vfork(2) system call compatible with 4.4BSD (i.e. BSD with Mach VM).
  128  * Address space is not shared, but parent is blocked until child exit.
  129  */
  130 /*ARGSUSED*/
  131 int
  132 sys_vfork(struct lwp *l, void *v, register_t *retval)
  133 {
  134 
  135         return (fork1(l, FORK_PPWAIT, SIGCHLD, NULL, 0, NULL, NULL,
  136             retval, NULL));
  137 }
  138 
  139 /*
  140  * New vfork(2) system call for NetBSD, which implements original 3BSD vfork(2)
  141  * semantics.  Address space is shared, and parent is blocked until child exit.
  142  */
  143 /*ARGSUSED*/
  144 int
  145 sys___vfork14(struct lwp *l, void *v, register_t *retval)
  146 {
  147 
  148         return (fork1(l, FORK_PPWAIT|FORK_SHAREVM, SIGCHLD, NULL, 0,
  149             NULL, NULL, retval, NULL));
  150 }
  151 
  152 /*
  153  * Linux-compatible __clone(2) system call.
  154  */
  155 int
  156 sys___clone(struct lwp *l, void *v, register_t *retval)
  157 {
  158         struct sys___clone_args /* {
  159                 syscallarg(int) flags;
  160                 syscallarg(void *) stack;
  161         } */ *uap = v;
  162         int flags, sig;
  163 
  164         /*
  165          * We don't support the CLONE_PID or CLONE_PTRACE flags.
  166          */
  167         if (SCARG(uap, flags) & (CLONE_PID|CLONE_PTRACE))
  168                 return (EINVAL);
  169 
  170         /*
  171          * Linux enforces CLONE_VM with CLONE_SIGHAND, do same.
  172          */
  173         if (SCARG(uap, flags) & CLONE_SIGHAND
  174             && (SCARG(uap, flags) & CLONE_VM) == 0)
  175                 return (EINVAL);
  176 
  177         flags = 0;
  178 
  179         if (SCARG(uap, flags) & CLONE_VM)
  180                 flags |= FORK_SHAREVM;
  181         if (SCARG(uap, flags) & CLONE_FS)
  182                 flags |= FORK_SHARECWD;
  183         if (SCARG(uap, flags) & CLONE_FILES)
  184                 flags |= FORK_SHAREFILES;
  185         if (SCARG(uap, flags) & CLONE_SIGHAND)
  186                 flags |= FORK_SHARESIGS;
  187         if (SCARG(uap, flags) & CLONE_VFORK)
  188                 flags |= FORK_PPWAIT;
  189 
  190         sig = SCARG(uap, flags) & CLONE_CSIGNAL;
  191         if (sig < 0 || sig >= _NSIG)
  192                 return (EINVAL);
  193 
  194         /*
  195          * Note that the Linux API does not provide a portable way of
  196          * specifying the stack area; the caller must know if the stack
  197          * grows up or down.  So, we pass a stack size of 0, so that the
  198          * code that makes this adjustment is a noop.
  199          */
  200         return (fork1(l, flags, sig, SCARG(uap, stack), 0,
  201             NULL, NULL, retval, NULL));
  202 }
  203 
  204 /* print the 'table full' message once per 10 seconds */
  205 struct timeval fork_tfmrate = { 10, 0 };
  206 
  207 int
  208 fork1(struct lwp *l1, int flags, int exitsig, void *stack, size_t stacksize,
  209     void (*func)(void *), void *arg, register_t *retval,
  210     struct proc **rnewprocp)
  211 {
  212         struct proc     *p1, *p2, *parent;
  213         uid_t           uid;
  214         struct lwp      *l2;
  215         int             count, s;
  216         vaddr_t         uaddr;
  217         boolean_t       inmem;
  218 
  219         /*
  220          * Although process entries are dynamically created, we still keep
  221          * a global limit on the maximum number we will create.  Don't allow
  222          * a nonprivileged user to use the last few processes; don't let root
  223          * exceed the limit. The variable nprocs is the current number of
  224          * processes, maxproc is the limit.
  225          */
  226         p1 = l1->l_proc;
  227         uid = p1->p_cred->p_ruid;
  228         if (__predict_false((nprocs >= maxproc - 5 && uid != 0) ||
  229                             nprocs >= maxproc)) {
  230                 static struct timeval lasttfm;
  231 
  232                 if (ratecheck(&lasttfm, &fork_tfmrate))
  233                         tablefull("proc", "increase kern.maxproc or NPROC");
  234                 if (forkfsleep)
  235                         (void)tsleep(&nprocs, PUSER, "forkmx", forkfsleep);
  236                 return (EAGAIN);
  237         }
  238         nprocs++;
  239 
  240         /*
  241          * Increment the count of procs running with this uid. Don't allow
  242          * a nonprivileged user to exceed their current limit.
  243          */
  244         count = chgproccnt(uid, 1);
  245         if (__predict_false(uid != 0 && count >
  246                             p1->p_rlimit[RLIMIT_NPROC].rlim_cur)) {
  247                 (void)chgproccnt(uid, -1);
  248                 nprocs--;
  249                 if (forkfsleep)
  250                         (void)tsleep(&nprocs, PUSER, "forkulim", forkfsleep);
  251                 return (EAGAIN);
  252         }
  253 
  254         /*
  255          * Allocate virtual address space for the U-area now, while it
  256          * is still easy to abort the fork operation if we're out of
  257          * kernel virtual address space.  The actual U-area pages will
  258          * be allocated and wired in uvm_fork() if needed.
  259          */
  260 
  261         inmem = uvm_uarea_alloc(&uaddr);
  262         if (__predict_false(uaddr == 0)) {
  263                 (void)chgproccnt(uid, -1);
  264                 nprocs--;
  265                 return (ENOMEM);
  266         }
  267 
  268         /*
  269          * We are now committed to the fork.  From here on, we may
  270          * block on resources, but resource allocation may NOT fail.
  271          */
  272 
  273         /* Allocate new proc. */
  274         p2 = proc_alloc();
  275 
  276         /*
  277          * Make a proc table entry for the new process.
  278          * Start by zeroing the section of proc that is zero-initialized,
  279          * then copy the section that is copied directly from the parent.
  280          */
  281         memset(&p2->p_startzero, 0,
  282             (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero));
  283         memcpy(&p2->p_startcopy, &p1->p_startcopy,
  284             (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy));
  285 
  286         simple_lock_init(&p2->p_sigctx.ps_silock);
  287         CIRCLEQ_INIT(&p2->p_sigctx.ps_siginfo);
  288         simple_lock_init(&p2->p_lock);
  289         LIST_INIT(&p2->p_lwps);
  290 
  291         /*
  292          * Duplicate sub-structures as needed.
  293          * Increase reference counts on shared objects.
  294          * The p_stats and p_sigacts substructs are set in uvm_fork().
  295          * Inherit SUGID, STOPFORK and STOPEXEC flags.
  296          */
  297         p2->p_flag = p1->p_flag & (P_SUGID | P_STOPFORK | P_STOPEXEC);
  298         p2->p_emul = p1->p_emul;
  299         p2->p_execsw = p1->p_execsw;
  300 
  301         if (p1->p_flag & P_PROFIL)
  302                 startprofclock(p2);
  303         p2->p_cred = pool_get(&pcred_pool, PR_WAITOK);
  304         memcpy(p2->p_cred, p1->p_cred, sizeof(*p2->p_cred));
  305         p2->p_cred->p_refcnt = 1;
  306         crhold(p1->p_ucred);
  307 
  308         LIST_INIT(&p2->p_raslist);
  309 #if defined(__HAVE_RAS)
  310         ras_fork(p1, p2);
  311 #endif
  312 
  313         /* bump references to the text vnode (for procfs) */
  314         p2->p_textvp = p1->p_textvp;
  315         if (p2->p_textvp)
  316                 VREF(p2->p_textvp);
  317 
  318         if (flags & FORK_SHAREFILES)
  319                 fdshare(p1, p2);
  320         else if (flags & FORK_CLEANFILES)
  321                 p2->p_fd = fdinit(p1);
  322         else
  323                 p2->p_fd = fdcopy(p1);
  324 
  325         if (flags & FORK_SHARECWD)
  326                 cwdshare(p1, p2);
  327         else
  328                 p2->p_cwdi = cwdinit(p1);
  329 
  330         /*
  331          * If p_limit is still copy-on-write, bump refcnt,
  332          * otherwise get a copy that won't be modified.
  333          * (If PL_SHAREMOD is clear, the structure is shared
  334          * copy-on-write.)
  335          */
  336         if (p1->p_limit->p_lflags & PL_SHAREMOD)
  337                 p2->p_limit = limcopy(p1->p_limit);
  338         else {
  339                 simple_lock(&p1->p_limit->p_slock);
  340                 p1->p_limit->p_refcnt++;
  341                 simple_unlock(&p1->p_limit->p_slock);
  342                 p2->p_limit = p1->p_limit;
  343         }
  344 
  345         if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
  346                 p2->p_flag |= P_CONTROLT;
  347         if (flags & FORK_PPWAIT)
  348                 p2->p_flag |= P_PPWAIT;
  349         parent = (flags & FORK_NOWAIT) ? initproc : p1;
  350         p2->p_pptr = parent;
  351         LIST_INIT(&p2->p_children);
  352 
  353         s = proclist_lock_write();
  354         LIST_INSERT_AFTER(p1, p2, p_pglist);
  355         LIST_INSERT_HEAD(&parent->p_children, p2, p_sibling);
  356         proclist_unlock_write(s);
  357 
  358 #ifdef KTRACE
  359         /*
  360          * Copy traceflag and tracefile if enabled.
  361          * If not inherited, these were zeroed above.
  362          */
  363         if (p1->p_traceflag & KTRFAC_INHERIT) {
  364                 p2->p_traceflag = p1->p_traceflag;
  365                 if ((p2->p_tracep = p1->p_tracep) != NULL)
  366                         ktradref(p2);
  367         }
  368 #endif
  369 
  370         scheduler_fork_hook(p1, p2);
  371 
  372         /*
  373          * Create signal actions for the child process.
  374          */
  375         sigactsinit(p2, p1, flags & FORK_SHARESIGS);
  376 
  377         /*
  378          * p_stats.
  379          * Copy parts of p_stats, and zero out the rest.
  380          */
  381         p2->p_stats = pstatscopy(p1->p_stats);
  382 
  383         /*
  384          * If emulation has process fork hook, call it now.
  385          */
  386         if (p2->p_emul->e_proc_fork)
  387                 (*p2->p_emul->e_proc_fork)(p2, p1, flags);
  388 
  389         /*
  390          * ...and finally, any other random fork hooks that subsystems
  391          * might have registered.
  392          */
  393         doforkhooks(p2, p1);
  394 
  395         /*
  396          * This begins the section where we must prevent the parent
  397          * from being swapped.
  398          */
  399         PHOLD(l1);
  400 
  401         uvm_proc_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE);
  402 
  403         /*
  404          * Finish creating the child process.
  405          * It will return through a different path later.
  406          */
  407         newlwp(l1, p2, uaddr, inmem, 0, stack, stacksize,
  408             (func != NULL) ? func : child_return,
  409             arg, &l2);
  410 
  411         /* Now safe for scheduler to see child process */
  412         s = proclist_lock_write();
  413         p2->p_exitsig = exitsig;                /* signal for parent on exit */
  414         LIST_INSERT_HEAD(&allproc, p2, p_list);
  415         proclist_unlock_write(s);
  416 
  417 #ifdef SYSTRACE
  418         /* Tell systrace what's happening. */
  419         if (ISSET(p1->p_flag, P_SYSTRACE))
  420                 systrace_sys_fork(p1, p2);
  421 #endif
  422 
  423 #ifdef __HAVE_SYSCALL_INTERN
  424         (*p2->p_emul->e_syscall_intern)(p2);
  425 #endif
  426 
  427         /*
  428          * Make child runnable, set start time, and add to run queue
  429          * except if the parent requested the child to start in SSTOP state.
  430          */
  431         SCHED_LOCK(s);
  432         p2->p_stats->p_start = time;
  433         p2->p_acflag = AFORK;
  434         if (p1->p_flag & P_STOPFORK) {
  435                 p2->p_nrlwps = 0;
  436                 p1->p_nstopchild++;
  437                 p2->p_stat = SSTOP;
  438                 l2->l_stat = LSSTOP;
  439         } else {
  440                 p2->p_nrlwps = 1;
  441                 p2->p_stat = SACTIVE;
  442                 l2->l_stat = LSRUN;
  443                 setrunqueue(l2);
  444         }
  445         SCHED_UNLOCK(s);
  446 
  447         /*
  448          * Now can be swapped.
  449          */
  450         PRELE(l1);
  451 
  452         /*
  453          * Notify any interested parties about the new process.
  454          */
  455         KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid);
  456 
  457         /*
  458          * Update stats now that we know the fork was successful.
  459          */
  460         uvmexp.forks++;
  461         if (flags & FORK_PPWAIT)
  462                 uvmexp.forks_ppwait++;
  463         if (flags & FORK_SHAREVM)
  464                 uvmexp.forks_sharevm++;
  465 
  466         /*
  467          * Pass a pointer to the new process to the caller.
  468          */
  469         if (rnewprocp != NULL)
  470                 *rnewprocp = p2;
  471 
  472 #ifdef KTRACE
  473         if (KTRPOINT(p2, KTR_EMUL))
  474                 p2->p_traceflag |= KTRFAC_TRC_EMUL;
  475 #endif
  476 
  477         /*
  478          * Preserve synchronization semantics of vfork.  If waiting for
  479          * child to exec or exit, set P_PPWAIT on child, and sleep on our
  480          * proc (in case of exit).
  481          */
  482         if (flags & FORK_PPWAIT)
  483                 while (p2->p_flag & P_PPWAIT)
  484                         tsleep(p1, PWAIT, "ppwait", 0);
  485 
  486         /*
  487          * Return child pid to parent process,
  488          * marking us as parent via retval[1].
  489          */
  490         if (retval != NULL) {
  491                 retval[0] = p2->p_pid;
  492                 retval[1] = 0;
  493         }
  494 
  495         return (0);
  496 }
  497 
  498 #if defined(MULTIPROCESSOR)
  499 /*
  500  * XXX This is a slight hack to get newly-formed processes to
  501  * XXX acquire the kernel lock as soon as they run.
  502  */
  503 void
  504 proc_trampoline_mp(void)
  505 {
  506         struct lwp *l;
  507 
  508         l = curlwp;
  509 
  510         SCHED_ASSERT_UNLOCKED();
  511         KERNEL_PROC_LOCK(l);
  512 }
  513 #endif

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