linux-kernel - Call of /proc/ entry troughs a kernel bug

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Date:	Wed, 13 Apr 2011 13:36:31 +0100
From:	limp <johnkyr83@...mail.com>
To:	<linux-kernel@...r.kernel.org>
Subject: Call of /proc/ entry troughs a kernel bug

Hi all,

I am using a 2.6.31.8 vanilla kernel on a Debian "lenny" distro.

What I am trying to do is to create a module that creates a pseudo-file
named '/proc/myfile' which prints some messages on the screen.

My module compiles correctly and I am also inserting it (insmod) into the
kernel without a problem. The problem occurs when I am trying to call it
like that: 

$ cat /proc/myfile

When I am doing that, I am getting the following output:


Installing 'myfile' module
BUG: unable to handle kernel paging request at 5a58e10f
IP: [<5a58e10f>] 0x5a58e10f
*pde = 00000000 
Oops: 0000 [#1] PREEMPT 
last sysfs file:
/sys/devices/pci0000:00/0000:00:1d.2/usb3/3-2/3-2:1.0/host2/target2:0:0/2:0:
0:0/block/sdb/size
Modules linked in: myfile

Pid: 2150, comm: cat Not tainted (2.6.31.8 #3) 986LCD-M/mITX
EIP: 0060:[<5a58e10f>] EFLAGS: 00210206 CPU: 0
EIP is at 0x5a58e10f
EAX: d25c6ad8 EBX: 00000000 ECX: 00000006 EDX: d4652d00
ESI: d443c2a0 EDI: d44a67a0 EBP: d4619e8c ESP: d4619e68
 DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 0068
Process cat (pid: 2150, ti=d4618000 task=d463c9c0 task.ti=d4618000)
Stack:
 c10cfd2d d4652d00 d25c6ad8 5a58e10f 00000004 00000020 00000000 d4652d00
<0> d25c6ad8 d4619eac c1095f99 de92a200 d25b2c00 c114f913 d4652d00 d4619ef8
<0> d4619ef8 d4619ec8 c1096120 d4652d00 c10cfc0f d4652380 00000000 d4619ef8
Call Trace:
 [<c10cfd2d>] ? proc_reg_open+0x11e/0x1aa
 [<c1095f99>] ? __dentry_open+0x155/0x243
 [<c114f913>] ? security_inode_permission+0x1e/0x20
 [<c1096120>] ? nameidata_to_filp+0x2b/0x42
 [<c10cfc0f>] ? proc_reg_open+0x0/0x1aa
 [<c10a0c94>] ? do_filp_open+0x3e4/0x75b
 [<c10a106f>] ? getname+0x20/0xb6
 [<c10a9b8a>] ? alloc_fd+0xdb/0xee
 [<c1095d4d>] ? do_sys_open+0x4a/0xe2
 [<c1095e27>] ? sys_open+0x1e/0x26
 [<c1002a30>] ? sysenter_do_call+0x12/0x22
Code:  Bad EIP value.
EIP: [<5a58e10f>] 0x5a58e10f SS:ESP 0068:d4619e68
CR2: 000000005a58e10f
---[ end trace dcbe10409eb0e88c ]---


The code of my module is the following:


#include <linux/module.h>	// for init_module() 
#include <linux/proc_fs.h>	// for proc_create_data() 

char modname[] = "myfile";

int my_get_info( char *buf, char **start, off_t off, int count )
{
	int len = 1;
	printk( "I am inside my get info function! \n");
	return len;
}

static int __init my_init( void )
{
	printk( "<1>\nInstalling \'%s\' module\n", modname );
	proc_create_data( modname, 0, NULL, my_get_info, NULL ); 
	return	0;
}

static void __exit my_exit(void )
{
	remove_proc_entry( modname, NULL );
	printk( "<1>Removing \'%s\' module\n", modname );
}

module_init( my_init );
module_exit( my_exit );

MODULE_LICENSE("GPL");


Any help on trying to debug this problem will be greatly appreciated.

King regards,

John K.

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