When you run the program in attachment, *even as an ordinary user*, the kernel
panic. Tested kernel is a 2.6.11.7 vanilla with alleged .config. Tested with
similar configuration on both a qemu machine and a real one (only fs changes).
The code is taken by a program of mine, and slightly simplified, but don't
trust comments.

Keywords: ptrace, (p)thread
Kernel version: 2.6.11.7 vanilla
Output:

When the program is run, the kernel triggers a BUG(), and the following one is
repeated quite a lot of times, with increasing Call Trace:

 ------------[ cut here ]------------
kernel BUG at kernel/exit.c:520!
invalid operand: 0000 [#1]
CPU:    0
EIP:    0060:[<c0110cd0>]    Not tainted VLI
EFLAGS: 00000046   (2.6.11.7-crasher) 
EIP is at exit_notify+0x5c0/0x840
eax: d7fffb04   ebx: d7fffaa0   ecx: 00000000   edx: d7fff5fc
esi: d7fff5a0   edi: d75b8540   ebp: d7fff5a0   esp: d6fadf54
ds: 007b   es: 007b   ss: 0068
Process ptrace-thread-f (pid: 808, threadinfo=d6fac000 task=d7fff5a0)
Stack: c010d3b0 b7e9d2e8 00000001 d7fff5fc d7fff640 00000000 00000000 d7fff5fc 
       d6fadf74 d6fadf74 c138a560 d7fff5a0 00000000 00000000 c0111067 d7fff5a0 
       d6fac000 c01184d4 c0118ebe d6fac000 00000000 b7fc8934 d6fac000 c0111244 
Call Trace:
 [<c010d3b0>] mm_release+0x90/0xa0
 [<c0111067>] do_exit+0x117/0x280
 [<c01184d4>] signal_wake_up+0x24/0x30
 [<c0118ebe>] zap_other_threads+0x5e/0xb0
 [<c0111244>] do_group_exit+0x34/0x70
 [<c0102483>] syscall_call+0x7/0xb
Code: 0f 85 79 ff ff ff eb dc 8d 76 00 89 5c 24 08 31 c0 89 44 24 04 8b 83 84 00 00 00 89 04 24 e8 48 82 00 00 e9 0c fc ff ff 8d 76 00 <0f> 0b 08 02 ff cc 27 c0 e9 da fb ff ff 8d 76 00 0f 0b 05 02 ff 
 ------------[ cut here ]------------

Last time this appears, before outputting '=======================' endlessly,
has this form:

 ------------[ cut here ]------------
kernel BUG at kernel/exit.c:520!
invalid operand: 0000 [#19]
CPU:    0
EIP:    0060:[<c0110cd0>]    Not tainted VLI
EFLAGS: 00000046   (2.6.11.7-crasher) 
EIP is at exit_notify+0x5c0/0x840
eax: d7fffb04   ebx: d7fffaa0   ecx: d7fff5a0   edx: d7fff5fc
esi: d7fff5a0   edi: d75b8540   ebp: d7fff5a0   esp: d6fac2a4
ds: 007b   es: 007b   ss: 0068
Process ptrace-thread-f (pid: 808, threadinfo=d6fac000 task=d7fff5a0)
Stack: 0000000a d7fff5a0 c011356b d7fff5fc d7fff640 c027bc4c c0103130 d7fff5fc 
       d6fac2c4 d6fac2c4 00000000 d7fff5a0 0000000b 00000000 c0111067 d7fff5a0 
       d7fff5a0 ffffffff 0000007b d6fac000 00000000 c0103130 d7fff5a0 c0102d5e 
Call Trace:
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c019b912>] __delay+0x12/0x20
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c010bf6e>] scheduler_tick+0x9e/0x290
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c019b912>] __delay+0x12/0x20
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c01be900>] i8042_timer_func+0x0/0x20
 [<c010bf6e>] scheduler_tick+0x9e/0x290
 [<c01be900>] i8042_timer_func+0x0/0x20
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c019b912>] __delay+0x12/0x20
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c010bf6e>] scheduler_tick+0x9e/0x290
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c019b912>] __delay+0x12/0x20
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c010bf6e>] scheduler_tick+0x9e/0x290
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c019b912>] __delay+0x12/0x20
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c010bf6e>] scheduler_tick+0x9e/0x290
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c019b912>] __delay+0x12/0x20
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c010c10d>] scheduler_tick+0x23d/0x290
 [<c01172a2>] update_process_times+0x32/0x110
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c019b912>] __delay+0x12/0x20
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c010bf6e>] scheduler_tick+0x9e/0x290
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c019b912>] __delay+0x12/0x20
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c010bf6e>] scheduler_tick+0x9e/0x290
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c019b912>] __delay+0x12/0x20
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c010bf6e>] scheduler_tick+0x9e/0x290
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c019b912>] __delay+0x12/0x20
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c010bf6e>] scheduler_tick+0x9e/0x290
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c010bf6e>] scheduler_tick+0x9e/0x290
 [<c01064c4>] timer_interrupt+0x54/0xf0
 [<c011351e>] __do_softirq+0x2e/0x90
 [<c0124020>] handle_IRQ_event+0x30/0x70
 [<c01240b1>] __do_IRQ+0x51/0xf0
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c010bf6e>] scheduler_tick+0x9e/0x290
 [<c01064c4>] timer_interrupt+0x54/0xf0
 [<c011351e>] __do_softirq+0x2e/0x90
 [<c0124020>] handle_IRQ_event+0x30/0x70
 [<c01240b1>] __do_IRQ+0x51/0xf0
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c010bf6e>] scheduler_tick+0x9e/0x290
 [<c01064c4>] timer_interrupt+0x54/0xf0
 [<c011351e>] __do_softirq+0x2e/0x90
 [<c0124020>] handle_IRQ_event+0x30/0x70
 [<c01240b1>] __do_IRQ+0x51/0xf0
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c019b912>] __delay+0x12/0x20
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c010bf6e>] scheduler_tick+0x9e/0x290
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c019b912>] __delay+0x12/0x20
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c010bf6e>] scheduler_tick+0x9e/0x290
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c019b912>] __delay+0x12/0x20
 [<c01c4ea0>] serial8250_console_write+0x160/0x250
 [<c010bf6e>] scheduler_tick+0x9e/0x290
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c010b6d2>] activate_task+0x62/0x80
 [<c010bf6e>] scheduler_tick+0x9e/0x290
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c011356b>] __do_softirq+0x7b/0x90
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0111067>] do_exit+0x117/0x280
 [<c0103130>] do_invalid_op+0x0/0xd0
 [<c0102d5e>] die+0x14e/0x150
 [<c01031e2>] do_invalid_op+0xb2/0xd0
 [<c0121b12>] get_futex_key+0x42/0x160
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c0121d26>] futex_wake+0x46/0xd0
 [<c012252c>] do_futex+0x6c/0xa0
 [<c010262b>] error_code+0x2b/0x30
 [<c0110cd0>] exit_notify+0x5c0/0x840
 [<c010d3b0>] mm_release+0x90/0xa0
 [<c0111067>] do_exit+0x117/0x280
 [<c01184d4>] signal_wake_up+0x24/0x30
 [<c0118ebe>] zap_other_threads+0x5e/0xb0
 [<c0111244>] do_group_exit+0x34/0x70
 [<c0102483>] syscall_call+0x7/0xb
 =======================

Software:
kernel was compiled under a system with the following characteristics:

>>>
If some fields are empty or look unusual you may have an old version.
Compare to the current minimal requirements in Documentation/Changes.
 
Linux ale 2.6.10-as3-virtuale #1 SMP Wed Feb 9 13:43:48 CET 2005 i686 GNU/Linux
 
Gnu C                  3.3.5
Gnu make               3.80
binutils               2.15
util-linux             2.12
mount                  2.12
module-init-tools      3.2-pre1
e2fsprogs              1.35
reiserfsprogs          line
reiser4progs           line
xfsprogs               2.6.20
quota-tools            3.12.
nfs-utils              1.0.6
Linux C Library        2.3.2
Dynamic linker (ldd)   2.3.2
Procps                 3.2.1
Net-tools              1.60
Console-tools          0.2.3
Sh-utils               5.2.1
./scripts/ver_linux: line 90: udevinfo: command not found
Modules Loaded         
>>>

And run on a qemu machine, between the others:

>>>
If some fields are empty or look unusual you may have an old version.
Compare to the current minimal requirements in Documentation/Changes.
 
Linux ubuntu-zoo 2.6.11.7-crasher #1 Tue Apr 19 22:08:08 CEST 2005 i686 GNU/Linux
 
Gnu C                  3.3.4
Gnu make               3.80
binutils               2.14.90.0.7
util-linux             2.12
mount                  2.12
module-init-tools      3.1-pre2
e2fsprogs              1.35
jfsutils               1.1.4
reiserfsprogs          3.6.17
reiser4progs           0.5.3
xfsprogs               2.6.18
Linux C Library        2.3.2
Dynamic linker (ldd)   2.3.2
Procps                 3.2.1
Net-tools              1.60
Console-tools          0.2.3
Sh-utils               5.0.91
udev                   026
>>>

But in fact I tried the original program (which shows the same behaviour) on at
least other two hardwares, with similar results, and this cut down version on
both qemu and my hardware, so I think it's quite indipendent.

I'm not subscribed to lkml, so please CC me in this thread.

-- 
Mat/tia Belletti             - Graduate student @ cs.unibo.it
ICQ: 33292311                - email: mbellett@cs.unibo.it
IRC: RedGlow                 - site(s): http://mbellett.web.cs.unibo.it/
RedGlow@jabber.linux.it/Gaim - Linux user 299762 @ machine 213003