[Devel] 2.6.20-lxc8: kernel panic with af_unix as module

[Pierre Peiffer]

Hi,

I'm trying to test this kernel with network namespace compiled. But I have a 
kernel panic (see below) during the boot when loading the module unix.ko (in 
af_unix_init).

After some search, it seems that specifying a particular section for some 
variables is incompatible with using them in a module.

In my case, when registering per_net__unix_root_table (in function 
unix_sysctl_register in file net/unix/sysctl_net_unix.c), it tries to access the 
child (which is per_net__unix_net_table) at the address 0x00000080 which is the 
address of this symbol in the section .data.pernet of the module object, but not 
a virtual address.

When compiling this in the kernel, there is no problem...
As I'm not familiar with the use of some sections in ELF format, I don't know 
how to correct this....

By the way, just for my knowledge, what is the advantage of specifying a 
particular section (.data.pernet in this case) for some variables ?

Thanks.

Here is the panic:
INIT: version 2.86 booting
NET: Registered protocol family 1
BUG: unable to handle kernel NULL pointer dereference at virtual address 00000080
  printing eip:
c0123bae
*pde = 00000000
Oops: 0000 [#1]
PREEMPT SMP
Modules linked in: unix ide_disk ide_core ahci libata sd_mod scsi_mod ehci_hcd 
uhci_hcd usbcore
CPU:    3
EIP:    0060:[<c0123bae>]    Not tainted VLI
EFLAGS: 00010282   (2.6.20-lxc8 #4)
EIP is at sysctl_net_table_fixup+0x7e/0xa0
eax: 37a65e00   ebx: 000000a8   ecx: ffffffff   edx: 00000080
esi: 00000080   edi: 37a65e00   ebp: f7ab1f00   esp: f7ab1ee0
ds: 007b   es: 007b   ss: 0068
Process modprobe (pid: 404, ti=f7ab0000 task=c232aa90 task.ti=f7ab0000)
Stack: f7e2dd08 37a65e00 37a65e00 f7ab1f00 c011d61b f7e2dd08 00000080 37a65e00
        f7ab1f28 c0123bab c0329260 00000080 00000000 00000000 00000000 f7e2c0a0
        37a65e00 c03c62a0 f7ab1f40 c01241cd f7e2dce0 c03c7f30 37a65e00 08060588
Call Trace:
  [<c010414a>] show_trace_log_lvl+0x1a/0x30
  [<c0104211>] show_stack_log_lvl+0xb1/0xe0
  [<c0104409>] show_registers+0x1c9/0x310
  [<c010466c>] die+0x11c/0x250
  [<c02c4213>] do_page_fault+0x2c3/0x5c0
  [<c02c27c4>] error_code+0x7c/0x84
  [<c0123bab>] sysctl_net_table_fixup+0x7b/0xa0
  [<c01241cd>] register_net_sysctl_table+0x2d/0x70
  [<f885b360>] unix_sysctl_register+0x20/0x30 [unix]
  [<f885859c>] unix_net_init+0x2c/0x40 [unix]
  [<c0271024>] register_pernet_operations+0x34/0xc0
  [<c027129c>] register_pernet_subsys+0x1c/0x30
  [<f882b04c>] af_unix_init+0x4c/0x54 [unix]
  [<c013bbc1>] sys_init_module+0x91/0x160
  [<c010313c>] syscall_call+0x7/0xb
  =======================
Code: f8 89 43 e0 89 f8 e8 d2 ee ff ff 8b 53 fc 89 43 f8 89 f8 e8 c5 ee ff ff 85 
f6 89 43 fc 74 09 89 f2 89 f8 e8 85 ff ff ff 83 c3 28 <8b>
43 d8 85 c0 75 8b 8b 73 dc 85 f6 75 84 83 c4 14 5b 5e 5f 5d
EIP: [<c0123bae>] sysctl_net_table_fixup+0x7e/0xa0 SS:ESP 0068:f7ab1ee0
                 Welcome to Fedora Core
                 Press 'I' to enter interactive startup.


-- 
Pierre
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