Bug 20671

------------------------------------------------------------------
the config file of kernel
------------------------------------------------------------------
#
# GENERIC -- Generic machine with WD/AHx/NCR/BTx family disks
#
# For more information on this file, please read the handbook section on
# Kernel Configuration Files:
#
#    http://www.freebsd.org/handbook/kernelconfig-config.html
#
# The handbook is also available locally in /usr/share/doc/handbook
# if you've installed the doc distribution, otherwise always see the
# FreeBSD World Wide Web server (http://www.FreeBSD.ORG/) for the
# latest information.
#
# An exhaustive list of options and more detailed explanations of the
# device lines is also present in the ./LINT configuration file. If you are
# in doubt as to the purpose or necessity of a line, check first in LINT.
#
# $FreeBSD: src/sys/i386/conf/GENERIC,v 1.143.2.22 1999/09/14 22:53:30 jkh Exp $

machine         "i386"
cpu             "I386_CPU"
cpu             "I486_CPU"
cpu             "I586_CPU"
cpu             "I686_CPU"
ident           bug
maxusers        256
makeoptions    DEBUG="-g"              #Build kernel with debug symbols.



options         MATH_EMULATE            #Support for x87 emulation
options         INET                    #InterNETworking
options         FFS                     #Berkeley Fast Filesystem
options         FFS_ROOT                #FFS usable as root device [keep this!]
options         MFS                     #Memory Filesystem
options         MFS_ROOT                #MFS usable as root device, "MFS" req'ed
options         NFS                     #Network Filesystem
options         NFS_ROOT                #NFS usable as root device, "NFS" req'ed
options         MSDOSFS                 #MSDOS Filesystem
options         "CD9660"                #ISO 9660 Filesystem
options         "CD9660_ROOT"           #CD-ROM usable as root. "CD9660" req'ed
options         PROCFS                  #Process filesystem
options         "COMPAT_43"             #Compatible with BSD 4.3 [KEEP THIS!]
options         SCSI_DELAY=15000        #Be pessimistic about Joe SCSI device
options         UCONSOLE                #Allow users to grab the console
options         FAILSAFE                #Be conservative
options         USERCONFIG              #boot -c editor
options         VISUAL_USERCONFIG       #visual boot -c editor
options         KTRACE                  #ktrace(1) syscall trace support
options         SYSVSHM                 #SYSV-style shared memory
options         SYSVMSG                 #SYSV-style message queues
options         SYSVSEM                 #SYSV-style semaphores

config          kernel  root on wd0

# To make an SMP kernel, the next two are needed
#options        SMP                     # Symmetric MultiProcessor Kernel
#options        APIC_IO                 # Symmetric (APIC) I/O
# Optionally these may need tweaked, (defaults shown):
#options        NCPU=2                  # number of CPUs
#options        NBUS=4                  # number of busses
#options        NAPIC=1                 # number of IO APICs
#options        NINTR=24                # number of INTs

controller      isa0
controller      pnp0                    # PnP support for ISA
controller      eisa0
controller      pci0

# Floppy drives
controller      fdc0    at isa? port "IO_FD1" bio irq 6 drq 2
disk            fd0     at fdc0 drive 0
disk            fd1     at fdc0 drive 1

# IDE controller and disks
options         "CMD640"        # work around CMD640 chip deficiency
controller      wdc0    at isa? port "IO_WD1" bio irq 14
disk            wd0     at wdc0 drive 0
disk            wd1     at wdc0 drive 1

controller      wdc1    at isa? port "IO_WD2" bio irq 15
disk            wd2     at wdc1 drive 0
disk            wd3     at wdc1 drive 1

# ATAPI devices
options         ATAPI           #Enable ATAPI support for IDE bus
options         ATAPI_STATIC    #Don't do it as an LKM
device          acd0            #IDE CD-ROM
device          wfd0            #IDE Floppy (e.g. LS-120)
# Proprietary or custom CD-ROM Interfaces
#device         wt0     at isa? port 0x300 bio irq 5 drq 1
#device         mcd0    at isa? port 0x300 bio irq 10
#device         matcd0  at isa? port 0x230 bio
#device         scd0    at isa? port 0x230 bio

# atkbdc0 controls both the keyboard and the PS/2 mouse
controller      atkbdc0 at isa? port IO_KBD tty
device          atkbd0  at isa? tty irq 1
device          psm0    at isa? tty irq 12

device          vga0    at isa? port ? conflicts

# splash screen/screen saver
pseudo-device   splash

# syscons is the default console driver, resembling an SCO console
device          sc0     at isa? tty

# Enable this and PCVT_FREEBSD for pcvt vt220 compatible console driver
#device         vt0     at isa? tty
#options        XSERVER                 # support for X server
#options        FAT_CURSOR              # start with block cursor
# If you have a ThinkPAD, uncomment this along with the rest of the PCVT lines
#options        PCVT_SCANSET=2          # IBM keyboards are non-std

# Floating point support - do not disable.
device          npx0    at isa? port IO_NPX irq 13

# Power management support (see LINT for more options)
device          apm0    at isa? disable flags 0x31 # Advanced Power Management

# PCCARD (PCMCIA) support

# Serial (COM) ports
device          sio0    at isa? port "IO_COM1" flags 0x10 tty irq 4
device          sio1    at isa? port "IO_COM2" tty irq 3
device          sio2    at isa? disable port "IO_COM3" tty irq 5
device          sio3    at isa? disable port "IO_COM4" tty irq 9

# Parallel port
device          ppc0    at isa? port? flags 0x40 net irq 7
controller      ppbus0                  # Parallel port bus (required)
device          lpt0    at ppbus?       # Printer
device          plip0   at ppbus?       # TCP/IP over parallel
device          ppi0    at ppbus?       # Parallel port interface device
#controller     vpo0    at ppbus?       # Requires scbus and da0

# PCI Ethernet NICs.
device          xl0             # 3Com 3c90x (``Boomerang'', ``Cyclone'')

# ISA Ethernet NICs.
# Order is important here due to intrusive probes, do *not* alphabetize
# this list of network interfaces until the probes have been fixed.
# Right now it appears that the ie0 must be probed before ep0. See
# revision 1.20 of this file.
# requires PCCARD (PCMCIA) support to be activated
#device         xe0     at isa? port? net irq ?

# PCCARD NIC drivers.
# ze and zp take over the pcic and cannot coexist with generic pccard
# support, nor the ed and ep drivers they replace.

# Pseudo devices - the number indicates how many units to allocated.
pseudo-device   loop            # Network loopback
pseudo-device   ether           # Ethernet support
pseudo-device   sl      1       # Kernel SLIP
pseudo-device   ppp     1       # Kernel PPP
pseudo-device   tun     1       # Packet tunnel
pseudo-device   pty     16      # Pseudo-ttys (telnet etc)
pseudo-device   gzip            # Exec gzipped a.out's

# The `bpfilter' pseudo-device enables the Berkeley Packet Filter.
# Be aware of the administrative consequences of enabling this!
# The number of devices determines the maximum number of
# simultaneous BPF clients programs runnable.
pseudo-device   bpfilter 1      #Berkeley packet filter
------------------------------------------------------------------
end of config file
------------------------------------------------------------------


------------------------------------------------------------------
This is the kgdb results
------------------------------------------------------------------
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This GDB was configured as "i386-unknown-freebsd"...
IdlePTD 2813952
initial pcb at 23ffb4
panicstr: page fault
panic messages:
---
Fatal trap 12: page fault while in kernel mode
fault virtual address   = 0x60000000
fault code              = supervisor read, page not present
instruction pointer     = 0x8:0xc01b8a74
stack pointer           = 0x10:0xc022b074
frame pointer           = 0x10:0xc022b080
code segment            = base rx0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, def32 1, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = Idle
interrupt mask          = net tty
trap number             = 12
panic: page fault

syncing disks... 7 7 done

dumping to dev 1, offset 319488
dump 143 142 141 140 139 138 137 136 135 134 133 132 131 130 129 128 127 126 125 124 123 122 121 120 1
19 118 117 116 115 114 113 112 111 110 109 108 107 106 105 104 103 102 101 100 99 98 97 96 95 94 93 92
 91 90 89 88 87 86 85 84 83 82 81 80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 60 59 58
 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24
 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
---
#0  0xc012f837 in boot ()
(kgdb) where
#0  0xc012f837 in boot ()
#1  0xc012fabc in at_shutdown ()
#2  0xc01f6c45 in trap_fatal ()
#3  0xc01f6923 in trap_pfault ()
#4  0xc01f659a in trap ()
#5  0xc01b8a74 in xl_newbuf ()
#6  0xc01b8bcd in xl_rxeof ()
#7  0xc01b925f in xl_intr ()
#8  0xc01f5551 in i686_pagezero ()
#9  0xc01faa47 in vm_page_zero_idle ()
--------------------------------------------------
end of kgdb
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~

Fix: 

I do not know
How-To-Repeat: Sometimes when I work with a network, I do ping another ... it happens.