kernel stack memory

[Denis Kirjanov]

At the moment of forking a new process do_fork() creates a new stack for the
task by using alloc_thread_info_node():

        struct page *page = alloc_pages_node(node, THREADINFO_GFP,
                                             THREAD_SIZE_ORDER);


On 9/13/12, Rajat Sharma <fs.rajat at gmail.com> wrote:
> "The kernel stack is part of task_struct of the running process"
>
> Please double check that, its not part of task_struct, rather on some
> architectures, kernel stack is extended by a thread_info structure at
> the end which keeps a link to task_struct of the process.
>
> -Rajat
>
> On Thu, Sep 13, 2012 at 1:59 PM, Arun KS <getarunks at gmail.com> wrote:
>> Hello Shubham,
>>
>> On Thu, Sep 13, 2012 at 12:15 PM, shubham sharma <shubham20006 at gmail.com>
>> wrote:
>>>
>>> Hi,
>>>
>>> As far as i know, the size of stack allocated in the kernel space is
>>> 8Kb for each process. But in case i use more than 8Kb of memory from
>>> the stack then what will happen? I think that in that case the system
>>> would crash because i am accessing an illegal memory area. I wrote
>>> kernel module in which i defined an integer array whose size was 8000.
>>> But still it did not crash my system. Why?
>>>
>>> The module i wrote was as follows:
>>>
>>> #include <linux/kernel.h>
>>> #include <linux/module.h>
>>>
>>> int __init init_my_module(void)
>>> {
>>>         int arr[8000];
>>>         printk("%s:%d\tmodule initilized\n", __func__, __LINE__);
>>>         arr[1] = 1;
>>>         arr[4000] = 1;
>>>         arr[7999] = 1;
>>
>> Instead do a memset.
>> memset(arr, 0, 8192);
>>
>> If you do this the current calling process thread_info will be set to
>> zero.
>> This should cause a crash.
>>
>> Thanks,
>> Arun
>>
>>
>>>
>>>         printk("%s:%d\tarr[1]:%d, arr[4000]:%d, arr[7999]:%d\n",
>>> __func__,
>>> __LINE__, arr[1], arr[4000], arr[7999]);
>>>         return 0;
>>> }
>>>
>>> void __exit cleanup_my_module(void)
>>> {
>>>         printk("exiting\n");
>>>         return;
>>> }
>>>
>>> module_init(init_my_module);
>>> module_exit(cleanup_my_module);
>>>
>>> MODULE_LICENSE("GPL");
>>>
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>>> Kernelnewbies at kernelnewbies.org
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>>
>>
>>
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>
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-- 
Regards,
Denis