add_timer crashes the kernel,Why?

add_timer crashes the kernel,Why?

[lijin liu]

Hello everyone!

I want to use the timer in my kernel module. I read the book  _Linux
kernel development 3rd version_  and LDD 3rd version.

Both the two books tell me write the code like this:

struct timer_list my_timer;
init_timer(&my_timer);

my_timer.expires = jiffies + wait;
my_timer.data = 0;
my_timer.function=my_function;

//active the timer:
add_timer(&timer);


When I insmod the module, the kernel crashed, and when I change my
code to *mod_timer* rather than add_timer.

It just works!

But why the add_timer crash the kernel?

add_timer crashes the kernel,Why?

[Raz]

try to remove mytimer from stack

On Mon, Dec 20, 2010 at 10:27 AM, lijin liu <llj098@gmail.com> wrote:

> Hello everyone!
>
> I want to use the timer in my kernel module. I read the book  _Linux
> kernel development 3rd version_  and LDD 3rd version.
>
> Both the two books tell me write the code like this:
>
> struct timer_list my_timer;
> init_timer(&my_timer);
>
> my_timer.expires = jiffies + wait;
> my_timer.data = 0;
> my_timer.function=my_function;
>
> //active the timer:
> add_timer(&timer);
>
>
> When I insmod the module, the kernel crashed, and when I change my
> code to *mod_timer* rather than add_timer.
>
> It just works!
>
> But why the add_timer crash the kernel?
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
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add_timer crashes the kernel,Why?

[Wick]

Hi Lijin:


On Mon, Dec 20, 2010 at 4:27 PM, lijin liu <llj098@gmail.com> wrote:
> Hello everyone!
>
> I want to use the timer in my kernel module. I read the book ?_Linux
> kernel development 3rd version_ ?and LDD 3rd version.
>
> Both the two books tell me write the code like this:
>
> struct timer_list my_timer;
> init_timer(&my_timer);
>
> my_timer.expires = jiffies + wait;
> my_timer.data = 0;
> my_timer.function=my_function;

You just constructed my_timer.

>
> //active the timer:
> add_timer(&timer);

and add timer (not my_timer )to the timer list ...

If the problem still exists, suggest you copy all codes and crash log here.

>
>
> When I insmod the module, the kernel crashed, and when I change my
> code to *mod_timer* rather than add_timer.

add_timer crashes the kernel,Why?

[lijin liu]

On Mon, Dec 20, 2010 at 4:42 PM, Raz <raziebe@gmail.com> wrote:
> try to remove mytimer from stack

Yes, I made a stupid mistake, It works now.

add_timer crashes the kernel,Why?

[Mulyadi Santosa]

On Mon, Dec 20, 2010 at 16:06, lijin liu <llj098@gmail.com> wrote:
> On Mon, Dec 20, 2010 at 4:42 PM, Raz <raziebe@gmail.com> wrote:
>> try to remove mytimer from stack
>
> Yes, I made a stupid mistake, It works now.

ah so you put all of the mentioned code in module_init? no wonder
then....init finishes...code and stack cleaned up....timer refers to
NULL...boom.

next time, please paste the exact code...so people didn't mis conclude
the statement....

-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com

add_timer crashes the kernel,Why?

[Mulyadi Santosa]

Hi :)

On Mon, Dec 20, 2010 at 15:27, lijin liu <llj098@gmail.com> wrote:
> Hello everyone!
>
> I want to use the timer in my kernel module. I read the book ?_Linux
> kernel development 3rd version_ ?and LDD 3rd version.
>
> Both the two books tell me write the code like this:
>
> struct timer_list my_timer;
> init_timer(&my_timer);
>
> my_timer.expires = jiffies + wait;
> my_timer.data = 0;
> my_timer.function=my_function;
>
> //active the timer:
> add_timer(&timer);
>
>
> When I insmod the module, the kernel crashed, and when I change my
> code to *mod_timer* rather than add_timer.

Hmmm, from http://lxr.linux.no/linux+v2.6.36/kernel/timer.c#L864, it reads:
void add_timer(struct timer_list *timer)
{
        BUG_ON(timer_pending(timer));
        mod_timer(timer, timer->expires);
}

thus, IMHO the error happened because there is other timer pending...
somehow it is forbidden to add timer when other are still in queue in
latest kernel

-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com

add_timer crashes the kernel,Why?

[Dexter Haslem]

On 12/20/2010 2:08 AM, Mulyadi Santosa wrote:
> Hi :)
>
> On Mon, Dec 20, 2010 at 15:27, lijin liu<llj098@gmail.com>  wrote:
>> Hello everyone!
>>
>> I want to use the timer in my kernel module. I read the book  _Linux
>> kernel development 3rd version_  and LDD 3rd version.
>>
>> Both the two books tell me write the code like this:
>>
>> struct timer_list my_timer;
>> init_timer(&my_timer);
>>
>> my_timer.expires = jiffies + wait;
>> my_timer.data = 0;
>> my_timer.function=my_function;
>>
>> //active the timer:
>> add_timer(&timer);
>>
>>
>> When I insmod the module, the kernel crashed, and when I change my
>> code to *mod_timer* rather than add_timer.
>
> Hmmm, from http://lxr.linux.no/linux+v2.6.36/kernel/timer.c#L864, it reads:
> void add_timer(struct timer_list *timer)
> {
>          BUG_ON(timer_pending(timer));
>          mod_timer(timer, timer->expires);
> }
>
> thus, IMHO the error happened because there is other timer pending...
> somehow it is forbidden to add timer when other are still in queue in
> latest kernel
>

I believe add_timer just prevents creating duplicate timers from the 
same struct. I was actually thinking I had the same problem with timer 
code (following essential linux device drivers). But the issue was 
removing a module with an active timer will cause a crash.

Here is what I ended up with, a silly sample timer that chains itself 3 
times. It might be useful to OP: http://pastebin.com/v4rr3t50

-- 
-Dexter Haslem