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 1.114.2.3 2004/08/15 14:06:29 tron Exp $ */
    2 
    3 /*-
    4  * Copyright (c) 1999, 2001 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  * 
   11  * Redistribution and use in source and binary forms, with or without  
   12  * modification, are permitted provided that the following conditions
   13  * are met:
   14  * 1. Redistributions of source code must retain the above copyright
   15  *    notice, this list of conditions and the following disclaimer.
   16  * 2. Redistributions in binary form must reproduce the above copyright
   17  *    notice, this list of conditions and the following disclaimer in the
   18  *    documentation and/or other materials provided with the distribution.
   19  * 3. All advertising materials mentioning features or use of this software
   20  *    must display the following acknowledgement:
   21  *      This product includes software developed by the NetBSD
   22  *      Foundation, Inc. and its contributors.
   23  * 4. Neither the name of The NetBSD Foundation nor the names of its
   24  *    contributors may be used to endorse or promote products derived
   25  *    from this software without specific prior written permission.
   26  * 
   27  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
   28  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   29  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   30  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
   31  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   32  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   33  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   34  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   35  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   36  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   37  * POSSIBILITY OF SUCH DAMAGE.
   38  */   
   39 
   40 /*
   41  * Copyright (c) 1982, 1986, 1989, 1991, 1993
   42  *      The Regents of the University of California.  All rights reserved.
   43  * (c) UNIX System Laboratories, Inc.
   44  * All or some portions of this file are derived from material licensed
   45  * to the University of California by American Telephone and Telegraph
   46  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
   47  * the permission of UNIX System Laboratories, Inc.
   48  *
   49  * Redistribution and use in source and binary forms, with or without
   50  * modification, are permitted provided that the following conditions
   51  * are met:
   52  * 1. Redistributions of source code must retain the above copyright
   53  *    notice, this list of conditions and the following disclaimer.
   54  * 2. Redistributions in binary form must reproduce the above copyright
   55  *    notice, this list of conditions and the following disclaimer in the
   56  *    documentation and/or other materials provided with the distribution.
   57  * 3. Neither the name of the University nor the names of its contributors
   58  *    may be used to endorse or promote products derived from this software
   59  *    without specific prior written permission.
   60  *
   61  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   62  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   63  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   64  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   65  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   66  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   67  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   68  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   69  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   70  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   71  * SUCH DAMAGE.
   72  *
   73  *      @(#)kern_fork.c 8.8 (Berkeley) 2/14/95
   74  */
   75 
   76 #include <sys/cdefs.h>
   77 __KERNEL_RCSID(0, "$NetBSD: kern_fork.c,v 1.114.2.3 2004/08/15 14:06:29 tron Exp $");
   78 
   79 #include "opt_ktrace.h"
   80 #include "opt_systrace.h"
   81 #include "opt_multiprocessor.h"
   82 
   83 #include <sys/param.h>
   84 #include <sys/systm.h>
   85 #include <sys/filedesc.h>
   86 #include <sys/kernel.h>
   87 #include <sys/malloc.h>
   88 #include <sys/pool.h>
   89 #include <sys/mount.h>
   90 #include <sys/proc.h>
   91 #include <sys/ras.h>
   92 #include <sys/resourcevar.h>
   93 #include <sys/vnode.h>
   94 #include <sys/file.h>
   95 #include <sys/acct.h>
   96 #include <sys/ktrace.h>
   97 #include <sys/vmmeter.h>
   98 #include <sys/sched.h>
   99 #include <sys/signalvar.h>
  100 #include <sys/systrace.h>
  101 
  102 #include <sys/sa.h>
  103 #include <sys/syscallargs.h>
  104 
  105 #include <uvm/uvm_extern.h>
  106 
  107 
  108 int     nprocs = 1;             /* process 0 */
  109 
  110 /*
  111  * Number of ticks to sleep if fork() would fail due to process hitting
  112  * limits. Exported in miliseconds to userland via sysctl.
  113  */
  114 int     forkfsleep = 0;
  115 
  116 /*ARGSUSED*/
  117 int
  118 sys_fork(struct lwp *l, void *v, register_t *retval)
  119 {
  120 
  121         return (fork1(l, 0, SIGCHLD, NULL, 0, NULL, NULL, retval, NULL));
  122 }
  123 
  124 /*
  125  * vfork(2) system call compatible with 4.4BSD (i.e. BSD with Mach VM).
  126  * Address space is not shared, but parent is blocked until child exit.
  127  */
  128 /*ARGSUSED*/
  129 int
  130 sys_vfork(struct lwp *l, void *v, register_t *retval)
  131 {
  132 
  133         return (fork1(l, FORK_PPWAIT, SIGCHLD, NULL, 0, NULL, NULL,
  134             retval, NULL));
  135 }
  136 
  137 /*
  138  * New vfork(2) system call for NetBSD, which implements original 3BSD vfork(2)
  139  * semantics.  Address space is shared, and parent is blocked until child exit.
  140  */
  141 /*ARGSUSED*/
  142 int
  143 sys___vfork14(struct lwp *l, void *v, register_t *retval)
  144 {
  145 
  146         return (fork1(l, FORK_PPWAIT|FORK_SHAREVM, SIGCHLD, NULL, 0,
  147             NULL, NULL, retval, NULL));
  148 }
  149 
  150 /*
  151  * Linux-compatible __clone(2) system call.
  152  */
  153 int
  154 sys___clone(struct lwp *l, void *v, register_t *retval)
  155 {
  156         struct sys___clone_args /* {
  157                 syscallarg(int) flags;
  158                 syscallarg(void *) stack;
  159         } */ *uap = v;
  160         int flags, sig;
  161 
  162         /*
  163          * We don't support the CLONE_PID or CLONE_PTRACE flags.
  164          */
  165         if (SCARG(uap, flags) & (CLONE_PID|CLONE_PTRACE))
  166                 return (EINVAL);
  167 
  168         /*
  169          * Linux enforces CLONE_VM with CLONE_SIGHAND, do same.
  170          */
  171         if (SCARG(uap, flags) & CLONE_SIGHAND
  172             && (SCARG(uap, flags) & CLONE_VM) == 0)
  173                 return (EINVAL);
  174 
  175         flags = 0;
  176 
  177         if (SCARG(uap, flags) & CLONE_VM)
  178                 flags |= FORK_SHAREVM;
  179         if (SCARG(uap, flags) & CLONE_FS)
  180                 flags |= FORK_SHARECWD;
  181         if (SCARG(uap, flags) & CLONE_FILES)
  182                 flags |= FORK_SHAREFILES;
  183         if (SCARG(uap, flags) & CLONE_SIGHAND)
  184                 flags |= FORK_SHARESIGS;
  185         if (SCARG(uap, flags) & CLONE_VFORK)
  186                 flags |= FORK_PPWAIT;
  187 
  188         sig = SCARG(uap, flags) & CLONE_CSIGNAL;
  189         if (sig < 0 || sig >= _NSIG)
  190                 return (EINVAL);
  191 
  192         /*
  193          * Note that the Linux API does not provide a portable way of
  194          * specifying the stack area; the caller must know if the stack
  195          * grows up or down.  So, we pass a stack size of 0, so that the
  196          * code that makes this adjustment is a noop.
  197          */
  198         return (fork1(l, flags, sig, SCARG(uap, stack), 0,
  199             NULL, NULL, retval, NULL));
  200 }
  201 
  202 /* print the 'table full' message once per 10 seconds */
  203 struct timeval fork_tfmrate = { 10, 0 };
  204 
  205 int
  206 fork1(struct lwp *l1, int flags, int exitsig, void *stack, size_t stacksize,
  207     void (*func)(void *), void *arg, register_t *retval,
  208     struct proc **rnewprocp)
  209 {
  210         struct proc     *p1, *p2, *parent;
  211         uid_t           uid;
  212         struct lwp      *l2;
  213         int             count, s;
  214         vaddr_t         uaddr;
  215         boolean_t       inmem;
  216 
  217         /*
  218          * Although process entries are dynamically created, we still keep
  219          * a global limit on the maximum number we will create.  Don't allow
  220          * a nonprivileged user to use the last few processes; don't let root
  221          * exceed the limit. The variable nprocs is the current number of
  222          * processes, maxproc is the limit.
  223          */
  224         p1 = l1->l_proc;
  225         uid = p1->p_cred->p_ruid;
  226         if (__predict_false((nprocs >= maxproc - 5 && uid != 0) ||
  227                             nprocs >= maxproc)) {
  228                 static struct timeval lasttfm;
  229 
  230                 if (ratecheck(&lasttfm, &fork_tfmrate))
  231                         tablefull("proc", "increase kern.maxproc or NPROC");
  232                 if (forkfsleep)
  233                         (void)tsleep(&nprocs, PUSER, "forkmx", forkfsleep);
  234                 return (EAGAIN);
  235         }
  236         nprocs++;
  237 
  238         /*
  239          * Increment the count of procs running with this uid. Don't allow
  240          * a nonprivileged user to exceed their current limit.
  241          */
  242         count = chgproccnt(uid, 1);
  243         if (__predict_false(uid != 0 && count >
  244                             p1->p_rlimit[RLIMIT_NPROC].rlim_cur)) {
  245                 (void)chgproccnt(uid, -1);
  246                 nprocs--;
  247                 if (forkfsleep)
  248                         (void)tsleep(&nprocs, PUSER, "forkulim", forkfsleep);
  249                 return (EAGAIN);
  250         }
  251 
  252         /*
  253          * Allocate virtual address space for the U-area now, while it
  254          * is still easy to abort the fork operation if we're out of
  255          * kernel virtual address space.  The actual U-area pages will
  256          * be allocated and wired in uvm_fork() if needed.
  257          */
  258 
  259         inmem = uvm_uarea_alloc(&uaddr);
  260         if (__predict_false(uaddr == 0)) {
  261                 (void)chgproccnt(uid, -1);
  262                 nprocs--;
  263                 return (ENOMEM);
  264         }
  265 
  266         /*
  267          * We are now committed to the fork.  From here on, we may
  268          * block on resources, but resource allocation may NOT fail.
  269          */
  270 
  271         /* Allocate new proc. */
  272         p2 = proc_alloc();
  273 
  274         /*
  275          * Make a proc table entry for the new process.
  276          * Start by zeroing the section of proc that is zero-initialized,
  277          * then copy the section that is copied directly from the parent.
  278          */
  279         memset(&p2->p_startzero, 0,
  280             (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero));
  281         memcpy(&p2->p_startcopy, &p1->p_startcopy,
  282             (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy));
  283 
  284         simple_lock_init(&p2->p_sigctx.ps_silock);
  285         CIRCLEQ_INIT(&p2->p_sigctx.ps_siginfo);
  286         simple_lock_init(&p2->p_lock);
  287         LIST_INIT(&p2->p_lwps);
  288 
  289         /*
  290          * Duplicate sub-structures as needed.
  291          * Increase reference counts on shared objects.
  292          * The p_stats and p_sigacts substructs are set in uvm_fork().
  293          */
  294         p2->p_flag = (p1->p_flag & P_SUGID);
  295         p2->p_emul = p1->p_emul;
  296         p2->p_execsw = p1->p_execsw;
  297 
  298         if (p1->p_flag & P_PROFIL)
  299                 startprofclock(p2);
  300         p2->p_cred = pool_get(&pcred_pool, PR_WAITOK);
  301         memcpy(p2->p_cred, p1->p_cred, sizeof(*p2->p_cred));
  302         p2->p_cred->p_refcnt = 1;
  303         crhold(p1->p_ucred);
  304 
  305         LIST_INIT(&p2->p_raslist);
  306 #if defined(__HAVE_RAS)
  307         ras_fork(p1, p2);
  308 #endif
  309 
  310         /* bump references to the text vnode (for procfs) */
  311         p2->p_textvp = p1->p_textvp;
  312         if (p2->p_textvp)
  313                 VREF(p2->p_textvp);
  314 
  315         if (flags & FORK_SHAREFILES)
  316                 fdshare(p1, p2);
  317         else if (flags & FORK_CLEANFILES)
  318                 p2->p_fd = fdinit(p1);
  319         else
  320                 p2->p_fd = fdcopy(p1);
  321 
  322         if (flags & FORK_SHARECWD)
  323                 cwdshare(p1, p2);
  324         else
  325                 p2->p_cwdi = cwdinit(p1);
  326 
  327         /*
  328          * If p_limit is still copy-on-write, bump refcnt,
  329          * otherwise get a copy that won't be modified.
  330          * (If PL_SHAREMOD is clear, the structure is shared
  331          * copy-on-write.)
  332          */
  333         if (p1->p_limit->p_lflags & PL_SHAREMOD)
  334                 p2->p_limit = limcopy(p1->p_limit);
  335         else {
  336                 p2->p_limit = p1->p_limit;
  337                 p2->p_limit->p_refcnt++;
  338         }
  339 
  340         /* Inherit STOPFORK and STOPEXEC flags */
  341         p2->p_flag |= p1->p_flag & (P_STOPFORK | P_STOPEXEC);
  342 
  343         if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
  344                 p2->p_flag |= P_CONTROLT;
  345         if (flags & FORK_PPWAIT)
  346                 p2->p_flag |= P_PPWAIT;
  347         parent = (flags & FORK_NOWAIT) ? initproc : p1;
  348         p2->p_pptr = parent;
  349         LIST_INIT(&p2->p_children);
  350 
  351         s = proclist_lock_write();
  352         LIST_INSERT_AFTER(p1, p2, p_pglist);
  353         LIST_INSERT_HEAD(&parent->p_children, p2, p_sibling);
  354         proclist_unlock_write(s);
  355 
  356 #ifdef KTRACE
  357         /*
  358          * Copy traceflag and tracefile if enabled.
  359          * If not inherited, these were zeroed above.
  360          */
  361         if (p1->p_traceflag & KTRFAC_INHERIT) {
  362                 p2->p_traceflag = p1->p_traceflag;
  363                 if ((p2->p_tracep = p1->p_tracep) != NULL)
  364                         ktradref(p2);
  365         }
  366 #endif
  367 
  368         scheduler_fork_hook(p1, p2);
  369 
  370         /*
  371          * Create signal actions for the child process.
  372          */
  373         sigactsinit(p2, p1, flags & FORK_SHARESIGS);
  374 
  375         /*
  376          * p_stats. 
  377          * Copy parts of p_stats, and zero out the rest.
  378          */
  379         p2->p_stats = pstatscopy(p1->p_stats);
  380 
  381         /*
  382          * If emulation has process fork hook, call it now.
  383          */
  384         if (p2->p_emul->e_proc_fork)
  385                 (*p2->p_emul->e_proc_fork)(p2, p1, flags);
  386 
  387         /*
  388          * ...and finally, any other random fork hooks that subsystems
  389          * might have registered.
  390          */
  391         doforkhooks(p2, p1);
  392 
  393         /*
  394          * This begins the section where we must prevent the parent
  395          * from being swapped.
  396          */
  397         PHOLD(l1);
  398 
  399         uvm_proc_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE);
  400 
  401         /*
  402          * Finish creating the child process.
  403          * It will return through a different path later.
  404          */
  405         newlwp(l1, p2, uaddr, inmem, 0, stack, stacksize, 
  406             (func != NULL) ? func : child_return, 
  407             arg, &l2);
  408 
  409         /* Now safe for scheduler to see child process */
  410         s = proclist_lock_write();
  411         p2->p_stat = SIDL;                      /* protect against others */
  412         p2->p_exitsig = exitsig;                /* signal for parent on exit */
  413         LIST_INSERT_HEAD(&allproc, p2, p_list);
  414         proclist_unlock_write(s);
  415 
  416 #ifdef SYSTRACE
  417         /* Tell systrace what's happening. */
  418         if (ISSET(p1->p_flag, P_SYSTRACE))
  419                 systrace_sys_fork(p1, p2);
  420 #endif
  421 
  422 #ifdef __HAVE_SYSCALL_INTERN
  423         (*p2->p_emul->e_syscall_intern)(p2);
  424 #endif
  425 
  426         /*
  427          * Make child runnable, set start time, and add to run queue
  428          * except if the parent requested the child to start in SSTOP state.
  429          */
  430         SCHED_LOCK(s);
  431         p2->p_stats->p_start = time;
  432         p2->p_acflag = AFORK;
  433         if (p1->p_flag & P_STOPFORK) {
  434                 p2->p_nrlwps = 0;
  435                 p1->p_nstopchild++;
  436                 p2->p_stat = SSTOP;
  437                 l2->l_stat = LSSTOP;
  438         } else {
  439                 p2->p_nrlwps = 1;
  440                 p2->p_stat = SACTIVE;
  441                 l2->l_stat = LSRUN;
  442                 setrunqueue(l2);
  443         }
  444         SCHED_UNLOCK(s);
  445 
  446         /*
  447          * Now can be swapped.
  448          */
  449         PRELE(l1);
  450 
  451         /*
  452          * Notify any interested parties about the new process.
  453          */
  454         KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid);
  455 
  456         /*
  457          * Update stats now that we know the fork was successful.
  458          */
  459         uvmexp.forks++;
  460         if (flags & FORK_PPWAIT)
  461                 uvmexp.forks_ppwait++;
  462         if (flags & FORK_SHAREVM)
  463                 uvmexp.forks_sharevm++;
  464 
  465         /*
  466          * Pass a pointer to the new process to the caller.
  467          */
  468         if (rnewprocp != NULL)
  469                 *rnewprocp = p2;
  470 
  471 #ifdef KTRACE
  472         if (KTRPOINT(p2, KTR_EMUL))
  473                 p2->p_traceflag |= KTRFAC_TRC_EMUL;
  474 #endif
  475 
  476         /*
  477          * Preserve synchronization semantics of vfork.  If waiting for
  478          * child to exec or exit, set P_PPWAIT on child, and sleep on our
  479          * proc (in case of exit).
  480          */
  481         if (flags & FORK_PPWAIT)
  482                 while (p2->p_flag & P_PPWAIT)
  483                         tsleep(p1, PWAIT, "ppwait", 0);
  484 
  485         /*
  486          * Return child pid to parent process,
  487          * marking us as parent via retval[1].
  488          */
  489         if (retval != NULL) {
  490                 retval[0] = p2->p_pid;
  491                 retval[1] = 0;
  492         }
  493 
  494         return (0);
  495 }
  496 
  497 #if defined(MULTIPROCESSOR)
  498 /*
  499  * XXX This is a slight hack to get newly-formed processes to
  500  * XXX acquire the kernel lock as soon as they run.
  501  */
  502 void
  503 proc_trampoline_mp(void)
  504 {
  505         struct lwp *l;
  506 
  507         l = curlwp;
  508 
  509         SCHED_ASSERT_UNLOCKED();
  510         KERNEL_PROC_LOCK(l);
  511 }
  512 #endif

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