Plug in USB-Memorystick. Wait a few seconds. 
$ mkdir/media/USB_DISK/foobar 
segmentation fault 
$ dmesg 
usb 1-1: new full speed USB device using uhci_hcd and address 2 
module_usb[5425]: main: action = 'add' 
module_usb[5425]: add: PRODUCT='(null)', TYPE = '(null)' 
module_usb[5425]: add: missing an environment variable, aborting. 
Initializing USB Mass Storage driver... 
scsi0 : SCSI emulation for USB Mass Storage devices 
usb-storage: device found at 2 
usb-storage: waiting for device to settle before scanning 
usbcore: registered new driver usb-storage 
USB Mass Storage support registered. 
  Vendor:           Model: USB DRIVE         Rev: 2.00 
  Type:   Direct-Access                      ANSI SCSI revision: 02 
sda: Unit Not Ready, sense: 
: Current: sense key: Unit Attention 
    Additional sense: Not ready to ready change, medium may have changed 
sda : READ CAPACITY failed. 
sda : status=1, message=00, host=0, driver=08  
sd: Current: sense key: Unit Attention 
    Additional sense: Not ready to ready change, medium may have changed 
sda: test WP failed, assume Write Enabled 
sda: assuming drive cache: write through 
sda: Unit Not Ready, sense: 
: Current: sense key: Unit Attention 
    Additional sense: Not ready to ready change, medium may have changed 
SCSI device sda: 2048000 512-byte hdwr sectors (1049 MB) 
sda: Write Protect is off 
sda: Mode Sense: 03 00 00 00 
sda: assuming drive cache: write through 
SCSI device sda: 2048000 512-byte hdwr sectors (1049 MB) 
sda: Write Protect is off 
sda: Mode Sense: 03 00 00 00 
sda: assuming drive cache: write through 
 sda: sda1 
Attached scsi removable disk sda at scsi0, channel 0, id 0, lun 0 
usb-storage: device scan complete 
Unable to handle kernel NULL pointer dereference at virtual address 00000004 
 printing eip: 
d8e9d340 
*pde = 00000000 
Oops: 0000 [#1] 
Modules linked in: nls_iso8859_1 nls_cp437 usb_storage hfsplus vfat fat subfs 
ip 
t_pkttype ipt_LOG ipt_limit speedstep_lib freq_table autofs4 thermal processor 
s 
nd_pcm_oss fan button battery snd_mixer_oss ac edd af_packet ipt_REJECT 
ipt_stat 
e iptable_mangle iptable_nat iptable_filter ip6table_mangle ip_conntrack 
ip_tabl 
es ip6table_filter ip6_tables ipv6 snd_via82xx gameport snd_ac97_codec 
snd_ac97_ 
bus snd_pcm snd_timer snd_page_alloc snd_mpu401_uart snd_rawmidi 
snd_seq_device  
snd soundcore i2c_viapro via686a i2c_sensor i2c_core tulip uhci_hcd usbcore 
via_ 
agp agpgart generic shpchp pci_hotplug video1394 ohci1394 raw1394 ieee1394 
parpo 
rt_pc lp parport dm_mod reiserfs via82cxxx ide_disk ide_cd ide_core sr_mod 
cdrom 
 sd_mod scsi_mod 
CPU:    0 
EIP:    0060:[<d8e9d340>]    Tainted: G     U VLI 
EFLAGS: 00210246   (2.6.13-rc5-git3-3-default)  
EIP is at subfs_lookup+0x40/0xd0 [subfs] 
eax: 00000000   ebx: cbbfa174   ecx: 00000000   edx: cbaab31c 
esi: ccacc2a0   edi: 00000000   ebp: 00000000   esp: cb419f30 
ds: 007b   es: 007b   ss: 0068 
Process mkdir (pid: 5513, threadinfo=cb418000 task=d60cc0a0) 
Stack: d8e9e980 cbaab31c 00000000 cb419f70 c0166598 cbbfa174 cb419f68 00000001  
       bfcd029b cb418000 c0167158 00000000 d7e01000 c016763c cbaf9d9c d7fe4d40  
       002a038d 00000003 d7e01010 00000000 00000000 00000000 c0108e94 00032e50  
Call Trace: 
 [<c0166598>] __lookup_hash+0x78/0x90 
 [<c0167158>] lookup_create+0x38/0x70 
 [<c016763c>] sys_mkdir+0x4c/0xc0 
 [<c0108e94>] do_mmap2+0x54/0xa0 
 [<c0102d1b>] sysenter_past_esp+0x54/0x79 
Code: 43 70 0f 8e 0a 05 00 00 ff 4e 14 0f 88 0e 05 00 00 31 c0 85 c0 74 14 ff 
4b 
 70 0f 88 0c 05 00 00 b8 00 fe ff ff 5b 5e 5f 5d c3 90 <8b> 51 04 89 f0 e8 06 
ff 
 ff ff 89 c7 ff 46 14 0f 8e f9 04 00 00  
 <6>usb 1-1: USB disconnect, address 2 
 
when not using mkdir, the usb-memorstick works perfectly well.