2012/10/19 Rohan Puri <rohan.puri15@xxxxxxxxx>
Hi Rohan,Hi Fan,On Fri, Oct 19, 2012 at 7:38 PM, Anuz Pratap Singh Tomar <chambilkethakur@xxxxxxxxx> wrote:
On Fri, Oct 19, 2012 at 2:46 PM, Fan Yang <lljyangfan@xxxxxxxxx> wrote:
2012/10/19 Arun KS <getarunks@xxxxxxxxx>
>
> Hi Fan,
>
> On Fri, Oct 19, 2012 at 6:50 PM, Fan Yang <lljyangfan@xxxxxxxxx> wrote:
>>
>> HI ALL:
>> I just run a module on my machine, but it can't work. When the module run the kernel will painc. I don't know where is wrong. This is my code:
>>
>> 1 #include<linux/module.h>
>> 2 #include<linux/kernel.h>
>> 3 #include<linux/init.h>
>> 4 #include<linux/sched.h>
>> 5
>> 6 int input = 1;
>> 7 module_param (input, int, S_IRUGO);
>> 8
>> 9 static int __init printvma_init (void)
>> 10 {
>> 11 struct vm_area_struct *p, *start;
>> 12 int i;
>> 13 struct task_struct *thread;
>> 14
>> 15 thread = current;
>> 16
>> 17 while (1)
>> 18 {
>> 19 if (thread->pid == input)
>> 20 break;
>> 21 thread = list_entry (thread->tasks.next, struct task_struct, tasks);
>> 22 }
>> 23 p = thread->mm->mmap;
>> 24
>> 25 do{
>> 26 printk ("%lx\t%lx\t%s\n", p->vm_start,\
>> 27 p->vm_end, p->vm_file->f_path.dentry->d_iname);
>> 28 p = p->vm_next;
>> 29 }while (p != NULL);
>> 30
>> 31 printk ("vm_file address is:%d\tf_path address is:%d\
>> 32 \tname is:%s",& p->vm_file->f_path,\
>> 33 p->vm_file->f_path.dentry->d_iname);
>> 34
>> 35 printk ("info from the kernel space:%s\n", thread->comm);
>> 36 return 0;
>> 37 }
>> 38
>> 39 static void __exit printvma_exit (void)
>> 40 {
>> 41 printk ("the module will leave the kernel space..\n");
>> 42 }
>> 43
>> 44 module_init (printvma_init);
>> 45 module_exit (printvma_exit);
>> 46 MODULE_LICENSE ("GPL");
>>
>>
>> what's wrong?
>
>
> It would be good if you paste your crash log here.
>
> Thanks,
> Arun
>>
>>
>> thanks
>>
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>>
>The module run in a virtual machine, I can't control the machine when it crashed, so I just got a picture when the kernel panic.
you can run the module under uml, it wont be hard to copy the crash log from terminal in uml.
Thanks
Fan
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See the issue is thread->mm is NULL in your case. The simplest way to test this in your case is by the following : -
Put these statements after the while loop
if(!thread->mm) { printk("thread->mm is NULL\n"); return 0; }
After this compile and load the module, you will see this statement printed in dmesg command output.
General programming practice : -
Always make checks for NULL pointer in your code, before dereferencing your code.
- Rohan
I don't think the thread->mm is NULL, because when I print the several vm_area_struct of the thread->mm it work well, but if put the code in the loop to print all the vma, it crashed.
Thinks
Fan
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