Hello ,
When you are declaring a variable inside a function it is pushed onto the stack.
The kernel stack is small , 4K so i guess that you somehow corrupt the stack.
thanks,
Daniel.
On Sun, Mar 8, 2009 at 11:55 AM, yogeshwar sonawane <yogyas@xxxxxxxxx> wrote:
> 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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>
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