add_timer crashes the kernel,Why?
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?
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?
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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.
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
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
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Mulyadi Santosa -
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