where are the bug ?

[Fan Yang]

2012/10/19 Rohan Puri <rohan.puri15 at gmail.com>

>
>
> On Fri, Oct 19, 2012 at 7:38 PM, Anuz Pratap Singh Tomar <
> chambilkethakur at gmail.com> wrote:
>
>>
>>
>> On Fri, Oct 19, 2012 at 2:46 PM, Fan Yang <lljyangfan at gmail.com> wrote:
>>
>>>
>>>
>>> 2012/10/19 Arun KS <getarunks at gmail.com>
>>> >
>>> > Hi Fan,
>>> >
>>> > On Fri, Oct 19, 2012 at 6:50 PM, Fan Yang <lljyangfan at gmail.com>
>>> 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
>>> >>
>>> >> _______________________________________________
>>> >> Kernelnewbies mailing list
>>> >> Kernelnewbies at kernelnewbies.org
>>> >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>>> >>
>>> >
>>> 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
>>>
>>> _______________________________________________
>>> Kernelnewbies mailing list
>>> Kernelnewbies at kernelnewbies.org
>>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>>>
>>>
>>
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>> Kernelnewbies mailing list
>> Kernelnewbies at kernelnewbies.org
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>>
>>
> Hi Fan,
>
> 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
>
Hi 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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