array declaration inside init function causing kernel panic

[yogeshwar sonawane <yogyas@xxxxxxxxx>]

Hi,

While doing some driver development, i was seeing a kernel panic.
After some trials, i found a simple condition which is triggering that
kernel panic.

I have declared an array having large interger elements(@2k) in
init_module(). The values are random/dummy.
The driver is a very simple code, just registering a character driver
in init_module() &
unregistering in cleanup_module() functions respectively.

After clean compilation, when i try to load my module, i see kernel
panic message(pasted below).
But, if i declare that array as a global variable(outside any
function), then it works fine. No any panic seen.

I tried putting the array in cleanup_module(), then also panic is
seen, but with some different messages.
I tried some different values in array, then also panic seen, but
messages are different.
my guess is that some corruption is happening inside kernel.

I just want to understand the reason behind this.
Is there any limit for local variables while writing drivers ?
How to know such limits ?

Kindly update me, if i am missing something very basic.
Any info/link/reference will be helpful.

For normal user processes, such large array declarations in a function
OR outside the function, does not create any problem.

I am using 2.6.9-42.ELsmp kernel (RHEL4-update 4,x86_64).

driver.c & Makefile are attached with this mail.

# insmod driver.ko
In init modulesize of array = 8992
The device is registered by Major no: 253
Unable to handle kernel NULL pointer dereference at 0000000000000048 RIP:
<ffffffff80139fa7>{do_exit+1027}
PML4 13364e067 PGD 0
Oops: 0000 [1] SMP
CPU 0
Modules linked in: driver(U) autofs4 i2c_dev i2c_core nfs lockd
nfs_acl sunrpc rdma_ucm(U) ib_sdp(U) rdma_cm(U) d
Pid: 4626, comm: insmod Not tainted 2.6.9-42.ELsmp
RIP: 0010:[<ffffffff80139fa7>] <ffffffff80139fa7>{do_exit+1027}
RSP: 0018:0000010133685f08  EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000010037c56780 RCX: 0000000000000014
RDX: 0000000000000056 RSI: 0000010001043380 RDI: 0000000000000000
RBP: 0000010037f08f40 R08: 0000010001043380 R09: 0000010001043380
R10: 0000000000000000 R11: 0000010037c56780 R12: 0000010037c56030
R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000502010
FS:  0000000000000000(0000) GS:ffffffff804e5080(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000000000048 CR3: 0000000000101000 CR4: 00000000000006e0
Process insmod (pid: 4626, threadinfo 0000010133684000, task 0000010037c56030)
Stack: d42e0180a6fb127c a643177c00000060 ffff0038d82e41b8 0000000000000000
      0000003556c2b110 0000003556c2b110 0000000000000000 0000000000000000
      0000007fbffff8f0 0000000000502030
Call Trace:<ffffffff8013a8f6>{sys_exit_group+0}
<ffffffff8011026a>{system_call+126}


Code: 48 8b 50 48 48 85 d2 74 29 65 8b 04 25 34 00 00 00 89 c0 48
RIP <ffffffff80139fa7>{do_exit+1027} RSP <0000010133685f08>
CR2: 0000000000000048
 <0>Kernel panic - not syncing: Oops


Thanks,
Yogeshwar


Note:- Earlier i tried to send the same mail with driver.c & Makefile
as attachments, but i think kernelnewbies mailing list does not accept
mails with attachments. Correct me, if i am wrong ? Now, i am pasting
the codes below.

driver.c :-

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>

struct file_operations fops;
static int major;

int mydevice_init_module(void)
{
   unsigned int array[] = {
    0x00000000, 0x00000000, 0x00000000, 0x00000000,
    0x12345678, 0x12345678, 0x12345678, 0x12345678,
    ......set any dummy/garbage values, .......................
    ................create large sized array..........................
    } ;

        printk("In init module");
        printk("size of array = %ld\n", sizeof(array)) ;
        major = register_chrdev(0,"mydevice",&fops);
        printk("\nThe device is registered by Major no: %d",major);
        if(major == -1)
                printk("\nError in registering the module");
        else
                printk("\n");
        return 0;
}

void mydevice_cleanup_module(void)
{
        unregister_chrdev(major,"mydevice");
        printk("In cleanup module");
}

static int my_open(struct inode *inode, struct file *file)
{
        printk("\nmydevice: open");
        return 0;
}

static int my_release(struct inode *inode, struct file *file)
{
        printk("\nmydevice: release");
        return 0;
}

struct file_operations fops =
{
        open: my_open,
        release: my_release,
};

module_init(mydevice_init_module);
module_exit(mydevice_cleanup_module);
MODULE_LICENSE("GPL");


Makefile :-

obj-m := driver.o
KDIR := /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
EXTRA_CFLAGS += -D DEBUG_INFO -D DEBUG_CRITICAL

default :
        $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules

clean :
        $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) clean

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