Re: Oops in kthread

From: Balbir Singh
Date: Sat May 20 2006 - 09:25:17 EST

On 5/20/06, Liu haixiang <liu.haixiang@xxxxxxxxx> wrote:
Hi All,

Today I debug one kernel thread created by kthread_run. And after
several hours run, there is one Oops coming from kthread. Please see
below mesage:
Unable to handle kernel NULL pointer dereference at virtual address 00000000
pc = 00000000
*pde = 00000000
Oops: 0000 [#1]

Pid : 261, Comm: CallbackManager
PC is at 0x0
PC : 00000000 SP : 869bbf8c SR : 40008100 TEA : c016db88 Tainted: P
R0 : 00000000 R1 : 00000000 R2 : 005770c5 R3 : 40008101
R4 : 8b000006 R5 : 00000003 R6 : 07b1ce60 R7 : 00000079
R8 : c01c0800 R9 : 07b1ce60 R10 : 00000003 R11 : 00000000
R12 : 0000004c R13 : 00000000 R14 : 00000079
MACH: 0000025c MACL: 000001c8 GBR : 00000000 PR : c01b514a

Your kernel is Tainted. I do not see a list of loaded modules in the
oops log. A quick grep through the kernel sources did not reveal any
routine called "CallbackManager". From the trace CallbackManager
(which is also the name of the thread) belongs to a module called

Are you writing fdma or do you have the source code for it? If your
planning to submit fdma to the linux kernel, I would recommend that
you go through the coding standards for the kernel. I don't think
CallbackManager is an acceptable naming convention.

Call trace:
[<8442d184>] kthread+0xe4/0x140
[<c01b4f80>] CallbackManager+0x0/0x2c0 [fdma]
[<8440f4c0>] complete+0x0/0xc0
[<8442d080>] kthread_should_stop+0x0/0x20
[<84403004>] kernel_thread_helper+0x4/0x20

Then I do objdump the kernel/kthread.c. Please see attached dumped
contents. And find the offset 0xe4. The assembly line code is:
e4: 08 20 tst r0,r0

Does anybody can explain to me which C code in kthread create this
Oops?Is there any easy way to translate assembly code to C?

Try running objdump -d -l on the object file. It should dump the line
numbers and the corresponding disassembled assembly code.

best regards

Liu haixiang

Linux Technology Center,
India Software Labs,
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