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

     /*      $NetBSD: kern_fork.c,v 1.128 2006/11/01 10:17:58 yamt Exp $     */
     
     /*-
      * Copyright (c) 1999, 2001, 2004 The NetBSD Foundation, Inc.
      * All rights reserved.
      *
      * This code is derived from software contributed to The NetBSD Foundation
      * by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
      * NASA Ames Research Center.
     * This code is derived from software contributed to The NetBSD Foundation
     * by Charles M. Hannum.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by the NetBSD
     *      Foundation, Inc. and its contributors.
     * 4. Neither the name of The NetBSD Foundation nor the names of its
     *    contributors may be used to endorse or promote products derived
     *    from this software without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     * POSSIBILITY OF SUCH DAMAGE.
     */
    
    /*
     * Copyright (c) 1982, 1986, 1989, 1991, 1993
     *      The Regents of the University of California.  All rights reserved.
     * (c) UNIX System Laboratories, Inc.
     * All or some portions of this file are derived from material licensed
     * to the University of California by American Telephone and Telegraph
     * Co. or Unix System Laboratories, Inc. and are reproduced herein with
     * the permission of UNIX System Laboratories, Inc.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)kern_fork.c 8.8 (Berkeley) 2/14/95
     */
    
    #include <sys/cdefs.h>
    __KERNEL_RCSID(0, "$NetBSD: kern_fork.c,v 1.128 2006/11/01 10:17:58 yamt Exp $");
    
    #include "opt_ktrace.h"
    #include "opt_systrace.h"
    #include "opt_multiprocessor.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/filedesc.h>
    #include <sys/kernel.h>
    #include <sys/malloc.h>
    #include <sys/pool.h>
    #include <sys/mount.h>
    #include <sys/proc.h>
    #include <sys/ras.h>
    #include <sys/resourcevar.h>
    #include <sys/vnode.h>
    #include <sys/file.h>
    #include <sys/acct.h>
    #include <sys/ktrace.h>
    #include <sys/vmmeter.h>
   #include <sys/sched.h>
   #include <sys/signalvar.h>
   #include <sys/systrace.h>
   #include <sys/kauth.h>
   
   #include <sys/sa.h>
   #include <sys/syscallargs.h>
   
   #include <uvm/uvm_extern.h>
   
   
   int     nprocs = 1;             /* process 0 */
   
   /*
    * Number of ticks to sleep if fork() would fail due to process hitting
    * limits. Exported in miliseconds to userland via sysctl.
    */
   int     forkfsleep = 0;
   
   /*ARGSUSED*/
   int
   sys_fork(struct lwp *l, void *v, register_t *retval)
   {
   
           return (fork1(l, 0, SIGCHLD, NULL, 0, NULL, NULL, retval, NULL));
   }
   
   /*
    * vfork(2) system call compatible with 4.4BSD (i.e. BSD with Mach VM).
    * Address space is not shared, but parent is blocked until child exit.
    */
   /*ARGSUSED*/
   int
   sys_vfork(struct lwp *l, void *v, register_t *retval)
   {
   
           return (fork1(l, FORK_PPWAIT, SIGCHLD, NULL, 0, NULL, NULL,
               retval, NULL));
   }
   
   /*
    * New vfork(2) system call for NetBSD, which implements original 3BSD vfork(2)
    * semantics.  Address space is shared, and parent is blocked until child exit.
    */
   /*ARGSUSED*/
   int
   sys___vfork14(struct lwp *l, void *v, register_t *retval)
   {
   
           return (fork1(l, FORK_PPWAIT|FORK_SHAREVM, SIGCHLD, NULL, 0,
               NULL, NULL, retval, NULL));
   }
   
   /*
    * Linux-compatible __clone(2) system call.
    */
   int
   sys___clone(struct lwp *l, void *v, register_t *retval)
   {
           struct sys___clone_args /* {
                   syscallarg(int) flags;
                   syscallarg(void *) stack;
           } */ *uap = v;
           int flags, sig;
   
           /*
            * We don't support the CLONE_PID or CLONE_PTRACE flags.
            */
           if (SCARG(uap, flags) & (CLONE_PID|CLONE_PTRACE))
                   return (EINVAL);
   
           /*
            * Linux enforces CLONE_VM with CLONE_SIGHAND, do same.
            */
           if (SCARG(uap, flags) & CLONE_SIGHAND
               && (SCARG(uap, flags) & CLONE_VM) == 0)
                   return (EINVAL);
   
           flags = 0;
   
           if (SCARG(uap, flags) & CLONE_VM)
                   flags |= FORK_SHAREVM;
           if (SCARG(uap, flags) & CLONE_FS)
                   flags |= FORK_SHARECWD;
           if (SCARG(uap, flags) & CLONE_FILES)
                   flags |= FORK_SHAREFILES;
           if (SCARG(uap, flags) & CLONE_SIGHAND)
                   flags |= FORK_SHARESIGS;
           if (SCARG(uap, flags) & CLONE_VFORK)
                   flags |= FORK_PPWAIT;
   
           sig = SCARG(uap, flags) & CLONE_CSIGNAL;
           if (sig < 0 || sig >= _NSIG)
                   return (EINVAL);
   
           /*
            * Note that the Linux API does not provide a portable way of
            * specifying the stack area; the caller must know if the stack
            * grows up or down.  So, we pass a stack size of 0, so that the
            * code that makes this adjustment is a noop.
            */
           return (fork1(l, flags, sig, SCARG(uap, stack), 0,
               NULL, NULL, retval, NULL));
   }
   
   /* print the 'table full' message once per 10 seconds */
   struct timeval fork_tfmrate = { 10, 0 };
   
   int
   fork1(struct lwp *l1, int flags, int exitsig, void *stack, size_t stacksize,
       void (*func)(void *), void *arg, register_t *retval,
       struct proc **rnewprocp)
   {
           struct proc     *p1, *p2, *parent;
           uid_t           uid;
           struct lwp      *l2;
           int             count, s;
           vaddr_t         uaddr;
           boolean_t       inmem;
   
           /*
            * Although process entries are dynamically created, we still keep
            * a global limit on the maximum number we will create.  Don't allow
            * a nonprivileged user to use the last few processes; don't let root
            * exceed the limit. The variable nprocs is the current number of
            * processes, maxproc is the limit.
            */
           p1 = l1->l_proc;
           uid = kauth_cred_getuid(p1->p_cred);
           if (__predict_false((nprocs >= maxproc - 5 && uid != 0) ||
                               nprocs >= maxproc)) {
                   static struct timeval lasttfm;
   
                   if (ratecheck(&lasttfm, &fork_tfmrate))
                           tablefull("proc", "increase kern.maxproc or NPROC");
                   if (forkfsleep)
                           (void)tsleep(&nprocs, PUSER, "forkmx", forkfsleep);
                   return (EAGAIN);
           }
           nprocs++;
   
           /*
            * Increment the count of procs running with this uid. Don't allow
            * a nonprivileged user to exceed their current limit.
            */
           count = chgproccnt(uid, 1);
           if (__predict_false(uid != 0 && count >
                               p1->p_rlimit[RLIMIT_NPROC].rlim_cur)) {
                   (void)chgproccnt(uid, -1);
                   nprocs--;
                   if (forkfsleep)
                           (void)tsleep(&nprocs, PUSER, "forkulim", forkfsleep);
                   return (EAGAIN);
           }
   
           /*
            * Allocate virtual address space for the U-area now, while it
            * is still easy to abort the fork operation if we're out of
            * kernel virtual address space.  The actual U-area pages will
            * be allocated and wired in uvm_fork() if needed.
            */
   
           inmem = uvm_uarea_alloc(&uaddr);
           if (__predict_false(uaddr == 0)) {
                   (void)chgproccnt(uid, -1);
                   nprocs--;
                   return (ENOMEM);
           }
   
           /*
            * We are now committed to the fork.  From here on, we may
            * block on resources, but resource allocation may NOT fail.
            */
   
           /* Allocate new proc. */
           p2 = proc_alloc();
   
           /*
            * Make a proc table entry for the new process.
            * Start by zeroing the section of proc that is zero-initialized,
            * then copy the section that is copied directly from the parent.
            */
           memset(&p2->p_startzero, 0,
               (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero));
           memcpy(&p2->p_startcopy, &p1->p_startcopy,
               (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy));
   
           simple_lock_init(&p2->p_sigctx.ps_silock);
           CIRCLEQ_INIT(&p2->p_sigctx.ps_siginfo);
           simple_lock_init(&p2->p_lock);
           LIST_INIT(&p2->p_lwps);
   
           /*
            * Duplicate sub-structures as needed.
            * Increase reference counts on shared objects.
            * The p_stats and p_sigacts substructs are set in uvm_fork().
            * Inherit flags we want to keep.  The flags related to SIGCHLD
            * handling are important in order to keep a consistent behaviour
            * for the child after the fork.
            */
           p2->p_flag = p1->p_flag & (P_SUGID | P_STOPFORK | P_STOPEXEC |
               P_NOCLDSTOP | P_NOCLDWAIT | P_CLDSIGIGN);
           p2->p_emul = p1->p_emul;
           p2->p_execsw = p1->p_execsw;
   
           if (p1->p_flag & P_PROFIL)
                   startprofclock(p2);
   
           kauth_cred_hold(p1->p_cred);
           p2->p_cred = p1->p_cred;
   
           LIST_INIT(&p2->p_raslist);
   #if defined(__HAVE_RAS)
           ras_fork(p1, p2);
   #endif
   
           /* bump references to the text vnode (for procfs) */
           p2->p_textvp = p1->p_textvp;
           if (p2->p_textvp)
                   VREF(p2->p_textvp);
   
           if (flags & FORK_SHAREFILES)
                   fdshare(p1, p2);
           else if (flags & FORK_CLEANFILES)
                   p2->p_fd = fdinit(p1);
           else
                   p2->p_fd = fdcopy(p1);
   
           if (flags & FORK_SHARECWD)
                   cwdshare(p1, p2);
           else
                   p2->p_cwdi = cwdinit(p1);
   
           /*
            * If p_limit is still copy-on-write, bump refcnt,
            * otherwise get a copy that won't be modified.
            * (If PL_SHAREMOD is clear, the structure is shared
            * copy-on-write.)
            */
           if (p1->p_limit->p_lflags & PL_SHAREMOD)
                   p2->p_limit = limcopy(p1->p_limit);
           else {
                   simple_lock(&p1->p_limit->p_slock);
                   p1->p_limit->p_refcnt++;
                   simple_unlock(&p1->p_limit->p_slock);
                   p2->p_limit = p1->p_limit;
           }
   
           if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
                   p2->p_flag |= P_CONTROLT;
           if (flags & FORK_PPWAIT)
                   p2->p_flag |= P_PPWAIT;
           parent = (flags & FORK_NOWAIT) ? initproc : p1;
           p2->p_pptr = parent;
           LIST_INIT(&p2->p_children);
   
           s = proclist_lock_write();
           LIST_INSERT_AFTER(p1, p2, p_pglist);
           LIST_INSERT_HEAD(&parent->p_children, p2, p_sibling);
           proclist_unlock_write(s);
   
   #ifdef KTRACE
           /*
            * Copy traceflag and tracefile if enabled.
            * If not inherited, these were zeroed above.
            */
           if (p1->p_traceflag & KTRFAC_INHERIT) {
                   p2->p_traceflag = p1->p_traceflag;
                   if ((p2->p_tracep = p1->p_tracep) != NULL)
                           ktradref(p2);
           }
   #endif
   
           scheduler_fork_hook(p1, p2);
   
           /*
            * Create signal actions for the child process.
            */
           sigactsinit(p2, p1, flags & FORK_SHARESIGS);
   
           /*
            * p_stats.
            * Copy parts of p_stats, and zero out the rest.
            */
           p2->p_stats = pstatscopy(p1->p_stats);
   
           /*
            * If emulation has process fork hook, call it now.
            */
           if (p2->p_emul->e_proc_fork)
                   (*p2->p_emul->e_proc_fork)(p2, p1, flags);
   
           /*
            * ...and finally, any other random fork hooks that subsystems
            * might have registered.
            */
           doforkhooks(p2, p1);
   
           /*
            * This begins the section where we must prevent the parent
            * from being swapped.
            */
           PHOLD(l1);
   
           uvm_proc_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE);
   
           /*
            * Finish creating the child process.
            * It will return through a different path later.
            */
           newlwp(l1, p2, uaddr, inmem, 0, stack, stacksize,
               (func != NULL) ? func : child_return,
               arg, &l2);
   
           /* Now safe for scheduler to see child process */
           s = proclist_lock_write();
           p2->p_exitsig = exitsig;                /* signal for parent on exit */
           LIST_INSERT_HEAD(&allproc, p2, p_list);
           proclist_unlock_write(s);
   
   #ifdef SYSTRACE
           /* Tell systrace what's happening. */
           if (ISSET(p1->p_flag, P_SYSTRACE))
                   systrace_sys_fork(p1, p2);
   #endif
   
   #ifdef __HAVE_SYSCALL_INTERN
           (*p2->p_emul->e_syscall_intern)(p2);
   #endif
   
           /*
            * Make child runnable, set start time, and add to run queue
            * except if the parent requested the child to start in SSTOP state.
            */
           SCHED_LOCK(s);
           getmicrotime(&p2->p_stats->p_start);
           p2->p_acflag = AFORK;
           if (p1->p_flag & P_STOPFORK) {
                   p2->p_nrlwps = 0;
                   p1->p_nstopchild++;
                   p2->p_stat = SSTOP;
                   l2->l_stat = LSSTOP;
           } else {
                   p2->p_nrlwps = 1;
                   p2->p_stat = SACTIVE;
                   l2->l_stat = LSRUN;
                   setrunqueue(l2);
           }
           SCHED_UNLOCK(s);
   
           /*
            * Now can be swapped.
            */
           PRELE(l1);
   
           /*
            * Notify any interested parties about the new process.
            */
           KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid);
   
           /*
            * Update stats now that we know the fork was successful.
            */
           uvmexp.forks++;
           if (flags & FORK_PPWAIT)
                   uvmexp.forks_ppwait++;
           if (flags & FORK_SHAREVM)
                   uvmexp.forks_sharevm++;
   
           /*
            * Pass a pointer to the new process to the caller.
            */
           if (rnewprocp != NULL)
                   *rnewprocp = p2;
   
   #ifdef KTRACE
           if (KTRPOINT(p2, KTR_EMUL))
                   p2->p_traceflag |= KTRFAC_TRC_EMUL;
   #endif
   
           /*
            * Preserve synchronization semantics of vfork.  If waiting for
            * child to exec or exit, set P_PPWAIT on child, and sleep on our
            * proc (in case of exit).
            */
           if (flags & FORK_PPWAIT)
                   while (p2->p_flag & P_PPWAIT)
                           tsleep(p1, PWAIT, "ppwait", 0);
   
           /*
            * Return child pid to parent process,
            * marking us as parent via retval[1].
            */
           if (retval != NULL) {
                   retval[0] = p2->p_pid;
                   retval[1] = 0;
           }
   
           return (0);
   }
   
   #if defined(MULTIPROCESSOR)
   /*
    * XXX This is a slight hack to get newly-formed processes to
    * XXX acquire the kernel lock as soon as they run.
    */
   void
   proc_trampoline_mp(void)
   {
           struct lwp *l;
   
           l = curlwp;
   
           SCHED_ASSERT_UNLOCKED();
           KERNEL_PROC_LOCK(l);
   }
   #endif

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