Kernel BUG in 2.6.38.2 slub.c when communicating via usb

[Oncaphillis]

 We are experiencing sporadic kernel bug messages and total
kernel freezes during usb communication via libusb-1.0.8

The communication should work as follows:

  - Send a 2 byte sequence to endpoint #4
    selecting the register to which the command should be send

  - The device should answer with the same two byte sequence
    on Endpoint #8

  - Send a 2 byte command sequence to endpoint #4

  - The device should acknowledge the command by returning
    the same two bytes on endpoint #8

  - The device may also initiate inbound data transfer on endpoint #8
    to inform about status changes.

We send the register selection and command data via

 libusb_bulk_transfer() with a time out of 10000 ms

 and read the reply via libusb_interrupt_transfer
 with a time out of 100  ms as specified for our device
 We also periodically read on endpoint #8 to get the
 status changes.
 Sometimes we run into the following situation.

 - We send the 2 byte register selection sequence via
   libusb_bulk_transfer
 - We try to read the response via libusb_interrupt_transfer but run
   into a time out or read junk (seems to be zero)
 - If we look at the USB communication via USB analyser we actually
   see the inbound transfer of the correct two bytes and the ACK by the
   kernel, but this data never ends up as a valid result of
   libusb_interrupt_transfer. Sometimes we get a timeout, sometimes we
   read junk.
 - Since we got a time out or junk data we retry the read up to 30
   times. Within  this polling we see the following kernel bug
   message in dmesg. Sometimes the kernel freezes completely

This BUG message is actually from a 2.6.30.10 kernel, but the
message is almost the same referring to a different line in slug.c
wher e it seems to complain that someone tries to free  memory
that has never been allocated.
The stack trace varies even for the same kernel versions.

The whole issue seems to vanish if the libusb has been compiled
with --enable-timerfd

The chipset on the host side is an Intel 82801I. The device Is A Sparta
Xilinx FPGA which seems to talk nicely to windows

A detailed screen shot of a USB analyzation can be found under

 http://www.oncaphillis.net/usb.pdf


<snip>
   ------------[ cut here ]------------
kernel BUG at mm/slub.c:2808!
invalid opcode: 0000 [#1] SMP
last sysfs file: 
/sys/devices/pci0000:00/0000:00:1d.7/usb2/2-3/bConfigurationValue
CPU 3
Modules linked in:
Pid: 4314, comm: rrdupdate Not tainted 2.6.30.10 #2 To Be Filled By O.E.M.
RIP: 0010:[<ffffffff8028d2f8>]  [<ffffffff8028d2f8>] kfree+0x7c/0xdb
RSP: 0000:ffff880077de1d38  EFLAGS: 00010246
RAX: 4000000000000000 RBX: ffff88007a07a772 RCX: ffff88007acea7e0
RDX: ffffe20000000000 RSI: ffffe20001ab1ab0 RDI: ffff88007a07a772
RBP: ffff880077de1d58 R08: 0000000000000000 R09: 0000000000000008
R10: 00000000f7f5e000 R11: 00000000f7f5d5b8 R12: ffff88007c081c80
R13: ffffffff802c9cd8 R14: 00000000f7f5e000 R15: ffff880077de1f58
FS:  0000000000000000(0000) GS:ffff88000105b000(0000) knlGS:0000000000000000
CS:  0010 DS: 002b ES: 002b CR0: 000000008005003b
CR2: 00000000f7f5d5b8 CR3: 0000000079940000 CR4: 00000000000406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process rrdupdate (pid: 4314, threadinfo ffff880077de0000, task 
ffff8800790d8b40)
Stack:
 00000000f7f5e000 0000000000000000 ffff88007c081c80 ffff880077d77800
 ffff880077de1e48 ffffffff802c9cd8 0000000000000080 ffff880077d77800
 0000000000000001 00000000f7f3d000 ffff880077df2000 ffff880077df2000
Call Trace:
 [<ffffffff802c9cd8>] load_elf_binary+0xfda/0x1862
 [<ffffffff802c0b6f>] ? compat_copy_strings+0x1b8/0x1ca
 [<ffffffff802958fe>] search_binary_handler+0xb0/0x23f
 [<ffffffff802c0dc7>] compat_do_execve+0x246/0x36f
 [<ffffffff8022593b>] sys32_execve+0x3e/0x5c
 [<ffffffff80225765>] ia32_ptregs_common+0x25/0x4c
Code: ba 00 00 00 00 00 e2 ff ff 48 c1 e8 0c 48 6b f0 38 48 01 d6 66 83 
3e 00 79 04 48 8b 76 10 48 8b 06 84 c0 78 14 66 a9 00 c0 75 04 <0f> 0b 
eb fe 48 89 f7 e8 35 13 fe ff eb 48 48 8b 4d 08 48 8b 7e
RIP  [<ffffffff8028d2f8>] kfree+0x7c/0xdb
 RSP <ffff880077de1d38>
---[ end trace ba800619f794f281 ]---

</snip>
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