(I'm forwarding this bug upstream on the behalf of another user,
for the original downstream bug report please see:
https://bugs.launchpad.net/ubuntu/+source/xorg-server/+bug/370851 )

Repro steps:

0. (using ubuntu 9.04 final; probably works on all xserver 1.6.0 systems though)

1. attach barcode reader hw to X of model [ref #1]
2. scan a barcode ==> immediate segv in xserver, return to GDM, fail.


ref #1: the specific barcode reader hw model is:
http://www.rakuten.co.jp/fksystem/702994/613735/

Here is the "bt full":

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0xb7a6d6d0 (LWP 4704)]
updateSlaveDeviceCoords (master=0x995c258, pDev=0x99e87f8)
    at ../../dix/getevents.c:168
168	../../dix/getevents.c: No such file or directory.
	in ../../dix/getevents.c
(gdb) backtrace full
#0  updateSlaveDeviceCoords (master=0x995c258, pDev=0x99e87f8)
    at ../../dix/getevents.c:168
	scr = (ScreenPtr) 0x0
	i = <value optimized out>
	lastSlave = <value optimized out>
#1  0x080a0958 in GetKeyboardValuatorEvents (events=0x95ad238, pDev=0x99e87f8, 
    type=2, key_code=13, first_valuator=0, num_valuators=0, valuators=0x0)
    at ../../dix/getevents.c:541
	numEvents = <value optimized out>
	ms = <value optimized out>
	sym = 52
	kbp = <value optimized out>
#2  0x080a0cda in GetKeyboardEvents (events=0x95ad238, pDev=0x99e87f8, type=2, 
    key_code=13) at ../../dix/getevents.c:743
No locals.
#3  0x080d817b in xf86PostKeyboardEvent (device=0x99e87f8, key_code=13, 
    is_down=1) at ../../../../hw/xfree86/common/xf86Xinput.c:931
	nevents = <value optimized out>
	i = <value optimized out>
	pointer = (DeviceIntPtr) 0x995be98
#4  0xb58893db in EvdevReadInput (pInfo=0x99b6de0) at ../../src/evdev.c:256
	ev = {time = {tv_sec = 1241755265, tv_usec = 788288}, type = 1, 
  code = 5, value = 1}
	len = <value optimized out>
	value = 1
	dx = 0
	dy = 0
	abs = 0
	button = 0
	pEvdev = (EvdevPtr) 0x99e7ce0
#5  0x080c7da7 in xf86SigioReadInput (fd=30, closure=0x99b6de0)
    at ../../../../hw/xfree86/common/xf86Events.c:311
	errno_save = 11
	sigstate = 1
#6  0x080b82cc in xf86SIGIO (sig=29)
    at ../../../../../hw/xfree86/os-support/linux/../shared/sigio.c:114
	i = 1
	ready = {fds_bits = {1073741824, 0 <repeats 31 times>}}
	to = {tv_sec = 0, tv_usec = 0}
	save_errno = 11
	r = 1
#7  <signal handler called>
No symbol table info available.
#8  0xb80c6430 in __kernel_vsyscall ()
No symbol table info available.
#9  0xb7d5e77d in ___newselect_nocancel () from /lib/tls/i686/cmov/libc.so.6
No locals.
#10 0x081329f0 in WaitForSomething (pClientsReady=0x99b3398)
    at ../../os/WaitFor.c:228
	i = <value optimized out>
	waittime = {tv_sec = 59, tv_usec = 249118}
	wt = (struct timeval *) 0xbfbe3600
	timeout = <value optimized out>
	clientsReadable = {fds_bits = {0 <repeats 32 times>}}
	clientsWritable = {fds_bits = {163428176, -1213807560, 163429268, 
    136208372, 163428200, 157825752, 157825752, 157950132, 2, 32, 2, 
    -1210183692, -1210179264, 163431936, -1078053544, -1211157066, 
    -1210179264, 163431936, 163431928, 136208372, 163431936, 163153512, 
    -1078053528, 135499809, 163431936, 136208372, -1078053464, 134696004, 
    163431936, 23069101, -1078053464, 4096}}
	curclient = <value optimized out>
	selecterr = 2264
	nready = <value optimized out>
	devicesReadable = {fds_bits = {163428176, -1235542028, -1078053720, 
    -1235570038, 163428176, 163428176, -1078053720, 135499809, -1231418896, 
    157825752, 163428200, -1232039351, 163428176, -1231312192, -1211159436, 
    134688279, 162560600, 157830496, -1211159436, 136208372, 163429260, 
    157825752, -1078053640, 135788002, 163428176, 136274600, 163431936, 
    -1210179264, 1, 32, -1078053576, -1213853672}}
	now = 429526
	someReady = 0
#11 0x0808d2be in Dispatch () at ../../dix/dispatch.c:367
	result = 0
	client = (ClientPtr) 0x9b079d0
	nready = -1
	start_tick = 360
#12 0x080722ed in main (argc=10, argv=0xbfbe3754, envp=0x0)
    at ../../dix/main.c:397
	i = <value optimized out>
	alwaysCheckForInput = {0, 1}