Bug 23379

	Null-modem connection between 2 machines (both running 4.2-S),
	connected via SLIP.  Transfer data between machines for a while, the
	"server" will lock up.

	server# /sbin/ifconfig sl0 inet 195.92.95.128 195.92.95.129 netmask 0xffffffff
	server# /sbin/sysctl -w net.inet.ip.forwarding=1
	server# /sbin/slattach -a -c -s 115200 -L -l cuaa0
	server# /usr/sbin/arp -s 195.92.95.129 0:90:27:b0:b2:2b pub

	client# /sbin/ifconfig sl0 inet 195.92.95.129 195.92.95.128 netmask 0xffffffff
	client# /sbin/slattach -a -c -s 115200 -L -l cuaa0
	client# route add default 195.92.95.128

	client$ ftp something, run cvsup, whatever.

	server# gdb -k /usr/obj/usr/src/sys/WEIRDO/kernel.debug /var/crash/vmcore.0
	GNU gdb 4.18
	Copyright 1998 Free Software Foundation, Inc.
	GDB is free software, covered by the GNU General Public License, and
	you are
	welcome to change it and/or distribute copies of it under certain
	conditions.
	Type "show copying" to see the conditions.
	There is absolutely no warranty for GDB.  Type "show warranty" for
	details.
	This GDB was configured as "i386-unknown-freebsd"...
	IdlePTD 3940352
	initial pcb at 2d9f00
	panicstr: page fault
	panic messages:
	---
	Fatal trap 12: page fault while in kernel mode
	fault virtual address   = 0x1ee9b6cf
	fault code              = supervisor read, page not present
	instruction pointer     = 0x8:0xc015d2a4
	stack pointer           = 0x10:0xc02937ec
	frame pointer           = 0x10:0xc02937f8
	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
	trap number             = 12
	panic: page fault

	syncing disks...

	Fatal trap 12: page fault while in kernel mode
	fault virtual address   = 0x30
	fault code              = supervisor read, page not present
	instruction pointer     = 0x8:0xc01dbf40
	stack pointer           = 0x10:0xc0293624
	frame pointer           = 0x10:0xc0293628
	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 bio cam
	trap number             = 12
	panic: page fault
	Uptime: 25m31s

	dumping to dev #ad/0x20006, offset 0
	dump ata0: resetting devices .. done
	256 255 254 253 252 251 250 249 248 247 246 245 244 243 242 241 240 239 238 237
	236 235 234 233 232 231 230 229 228 227 226 225 224 223 222 221 220 219 218 217
	216 215 214 213 212 211 210 209 208 207 206 205 204 203 202 201 200 199 198 197
	196 195 194 193 192 191 190 189 188 187 186 185 184 183 182 181 180 179 178 177
	176 175 174 173 172 171 170 169 168 167 166 165 164 163 162 161 160 159 158 157
	156 155 154 153 152 151 150 149 148 147 146 145 144 143 142 141 140 139 138 137
	136 135 134 133 132 131 130 129 128 127 126 125 124 123 122 121 120 119 118 117
	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  dumpsys () at /usr/src/sys/kern/kern_shutdown.c:469
	 469             if (dumping++) {
	 (kgdb) where
	#0  dumpsys () at /usr/src/sys/kern/kern_shutdown.c:469
	#1  0xc01431cf in boot (howto=260) at /usr/src/sys/kern/kern_shutdown.c:309
	#2  0xc0143565 in panic (fmt=0xc028ae0f "page fault")
	    at /usr/src/sys/kern/kern_shutdown.c:556
	#3  0xc024d94e in trap_fatal (frame=0xc02935e4, eva=48)
	    at /usr/src/sys/i386/i386/trap.c:951
	#4  0xc024d601 in trap_pfault (frame=0xc02935e4, usermode=0, eva=48)
	    at /usr/src/sys/i386/i386/trap.c:844
	#5  0xc024d1a3 in trap (frame={tf_fs = 6684688, tf_es = -1071054832
	      tf_ds = -1054474224, tf_edi = 0, tf_esi = -1054424576,
	      tf_ebp = -1071040984, tf_isp = -1071041008, tf_ebx = -1070970340,
	      tf_edx = 6864960, tf_ecx = -880820032, tf_eax = 0, tf_trapno = 12,
	      tf_err = 0, tf_eip = -1071792320, tf_cs = 8, tf_eflags = 66050,
	      tf_esp = -1054424576, tf_ss = -1071040952})
	    at /usr/src/sys/i386/i386/trap.c:443
	#6  0xc01dbf40 in acquire_lock (lk=0xc02a4a1c)
	    at /usr/src/sys/ufs/ffs/ffs_softdep.c:267
	#7  0xc01dfc28 in softdep_update_inodeblock (ip=0xc126c200, bp=0xc61c1838,
	    waitfor=0) at /usr/src/sys/ufs/ffs/ffs_softdep.c:3592
	#8  0xc01db211 in ffs_update (vp=0xcb7fc0c0, waitfor=0)
	    at /usr/src/sys/ufs/ffs/ffs_inode.c:106
	#9  0xc01e2f34 in ffs_sync (mp=0xc0f96600, waitfor=2, cred=0xc0a5f580,
	    p=0xc02f1920) at /usr/src/sys/ufs/ffs/ffs_vfsops.c:987
---Type <return> to continue, or q <return> to quit---
	#10 0xc01707df in sync (p=0xc02f1920, uap=0x0)
	    at /usr/src/sys/kern/vfs_syscalls.c:545
	#11 0xc0142faa in boot (howto=256) at /usr/src/sys/kern/kern_shutdown.c:233
	#12 0xc0143565 in panic (fmt=0xc028ae0f "page fault")
	    at /usr/src/sys/kern/kern_shutdown.c:556
	#13 0xc024d94e in trap_fatal (frame=0xc02937ac, eva=518633167)
	    at /usr/src/sys/i386/i386/trap.c:951
	#14 0xc024d601 in trap_pfault (frame=0xc02937ac, usermode=0, eva=518633167)
	    at /usr/src/sys/i386/i386/trap.c:844
	#15 0xc024d1a3 in trap (frame={tf_fs = 16, tf_es = 16, tf_ds = -1071054832,
	      tf_edi = 6686720, tf_esi = -1062538496, tf_ebp = -1071040520,
	      tf_isp = -1071040552, tf_ebx = 518633149, tf_edx = 0,
	      tf_ecx = -1062656000, tf_eax = -6686721, tf_trapno = 12, tf_err = 0,
	      tf_eip = -1072311644, tf_cs = 8, tf_eflags = 66054,
	      tf_esp = -1062538752, tf_ss = -1062538496})
	    at /usr/src/sys/i386/i386/trap.c:443
	#16 0xc015d2a4 in m_freem (m=0x1ee9b6bd) at /usr/src/sys/kern/uipc_mbuf.c:525
	#17 0xc015d2b8 in m_freem (m=0xc0a90a00) at /usr/src/sys/kern/uipc_mbuf.c:534
	#18 0xc01d1502 in fxp_stats_update (arg=0xc0ee2a00) at /usr/src/sys/pci/if_fxp.c:1366
	#19 0xc0148c7d in softclock () at /usr/src/sys/kern/kern_timeout.c:131
	
	
	server#
	machine		i386
	cpu		I686_CPU
	ident		WEIRDO
	maxusers	64
	makeoptions	DEBUG=-g
	options		INET
	options		INET6
	options		FFS
	options		FFS_ROOT
	options		SOFTUPDATES
	options		NFS
	options		CD9660
	options		PROCFS
	options		COMPAT_43
	options		UCONSOLE
	options		USERCONFIG
	options		SYSVSHM
	options		SYSVMSG
	options		SYSVSEM
	options		P1003_1B
	options		KBD_INSTALL_CDEV
	options		_KPOSIX_PRIORITY_SCHEDULING

	device		isa
	device		pci

	device		fdc0	at isa? port IO_FD1 irq 6 drq 2
	device		fd0	at fdc0 drive 0

	device		ata
	device		atadisk
	device		atapicd
	options		ATA_STATIC_ID
	options		ATA_ENABLE_ATAPI_DMA

	device		atkbdc0 at isa? port IO_KBD
	device		atkbd0  at atkbdc? irq 1 flags 0x1
	device		psm0    at atkbdc? irq 12
	device		vga0    at isa?

	device		sc0     at isa? flags 0x100

	device		npx0    at nexus? port IO_NPX irq 13

	device		sio0    at isa? port IO_COM1 flags 0x10 irq 4

	device		ppc0    at isa? irq 7
	device		ppbus
	device		lpt
	device		plip

	device		fxp0

	pseudo-device	loop
	pseudo-device	ether
	pseudo-device	sl	1
	pseudo-device	gif	1
	pseudo-device	pty
	pseudo-device	splash
	pseudo-device	gzip
	pseudo-device	bpf

	options		VESA
	options		DDB
	options		CPU_FASTER_5X86_FPU
	options		NFS_NOSERVER
	options		SC_DISABLE_REBOOT
	options		SC_HISTORY_SIZE=1000
	options		COMPAT_LINUX
	options		INCLUDE_CONFIG_FILE
	options		IPFIREWALL
	options		IPFIREWALL_VERBOSE
	options		IPFIREWALL_DEFAULT_TO_ACCEPT
	options		IPV6FIREWALL
	options		TCP_RESTRICT_RST
	options		IPDIVERT
	options		DUMMYNET
	options		BRIDGE

	device		pcm
	device		usb
	device		ugen
	device		uhid
	device		ums

	device		smb
	device		smbus
	device		intpm
	device		ichsmb
	device		ic
	device		iic
	device		iicsmb
	device		iicbus
	device		iicbb

	server# dmesg
	Copyright (c) 1992-2000 The FreeBSD Project.
	Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994
	        The Regents of the University of California. All rights reserved.
	FreeBSD 4.2-STABLE #0: Thu Dec  7 15:12:17 GMT 2000
	    sketchy@weirdo.netcraft.com:/usr/obj/usr/src/sys/WEIRDO
	Timecounter "i8254"  frequency 1193182 Hz
	Timecounter "TSC"  frequency 598624822 Hz
	CPU: Pentium III/Pentium III Xeon/Celeron (598.62-MHz 686-class CPU)
	  Origin = "GenuineIntel"  Id = 0x673  Stepping = 3
	  Features=0x383f9ff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,MMX,FXSR,SSE>
	real memory  = 268435456 (262144K bytes)
	avail memory = 257482752 (251448K bytes)
	Preloaded elf kernel "kernel" at 0xc03a3000.
	Preloaded elf module "splash_bmp.ko" at 0xc03a309c.
	Preloaded splash_image_data "/boot/splash.bmp" at 0xc03a3140.
	VESA: v2.0, 32768k memory, flags:0x1, mode table:0xc00c6954
	(c0006954)
	VESA: Matrox Graphics Inc.
	Pentium Pro MTRR support enabled
	npx0: <math processor> on motherboard
	npx0: INT 16 interface
	pcib0: <Intel 82443BX (440 BX) host to PCI bridge> on motherboard
	pci0: <PCI bus> on pcib0
	pcib1: <Intel 82443BX (440 BX) PCI-PCI (AGP) bridge> at device 1.0
	on pci0
	pci1: <PCI bus> on pcib1
	pci1: <Matrox MGA G400 AGP graphics accelerator> at 0.0 irq 11
	isab0: <Intel 82371AB PCI to ISA bridge> at device 7.0 on pci0
	isa0: <ISA bus> on isab0
	atapci0: <Intel PIIX4 ATA33 controller> port 0x10a0-0x10af at device 7.1 on pci0
	ata0: at 0x1f0 irq 14 on atapci0
	ata1: at 0x170 irq 15 on atapci0
	pci0: <Intel 82371AB/EB (PIIX4) USB controller> at 7.2 irq 9
	intpm0: <Intel 82371AB Power management controller> port 0x7000-0x700f irq 9 at device 7.3 on pci
	intpm0: I/O mapped 7000
	fxp0: <Intel Pro 10/100B/100+ Ethernet> port 0x1000-0x103f mem 0xd0000000-0xd00fffff,0xd0100000-0xd0100fff irq 11 at device 13.0 on pci0
	fxp0: Ethernet address 00:90:27:b0:b2:2b
	pcm0: <AudioPCI ES1371> port 0x1040-0x107f irq 10 at device 14.0 on
	pci0
	fdc0: <NEC 72065B or clone> at port 0x3f0-0x3f5,0x3f7 irq 6 drq 2 on
	isa0
	fdc0: FIFO enabled, 8 bytes threshold
	fd0: <1440-KB 3.5" drive> on fdc0 drive 0
	atkbdc0: <Keyboard controller (i8042)> at port 0x60,0x64 on isa0
	atkbd0: <AT Keyboard> flags 0x1 irq 1 on atkbdc0
	kbd0 at atkbd0
	psm0: <PS/2 Mouse> irq 12 on atkbdc0
	psm0: model Generic PS/2 mouse, device ID 0
	vga0: <Generic ISA VGA> at port 0x3c0-0x3df iomem 0xa0000-0xbffff on isa0
	sc0: <System console> at flags 0x100 on isa0
	sc0: VGA <16 virtual consoles, flags=0x300>
	sio0 at port 0x3f8-0x3ff irq 4 flags 0x10 on isa0
	sio0: type 16550A
	ppc0: <Parallel port> at port 0x378-0x37f irq 7 on isa0
	ppc0: Generic chipset (EPP/NIBBLE) in COMPATIBLE mode
	lpt0: <Printer> on ppbus0
	lpt0: Interrupt-driven port
	plip0: <PLIP network interface> on ppbus0
	DUMMYNET initialized (000608)
	IPv6 packet filtering initialized, logging disabled
	IP packet filtering initialized, divert enabled, rule-based forwarding disabled, default to accept, unlimited logging
	BRIDGE 990810, have 5 interfaces
	-- index 1  type 6 phy 0 addrl 6 addr 00.90.27.b0.b2.2b
	ad0: 14324MB <QUANTUM FIREBALLlct10 15> [29104/16/63] at ata0-master
	UDMA33
	acd0: CDROM <MATSHITA CR-583> at ata1-master using PIO3
	Mounting root from ufs:/dev/ad0s1a

How-To-Repeat: 
	The above crashes the server box 100% of the time, usually within 5/10
	minutes.  Has done for both 4.2-RELEASE and for every version of
	-stable since.