Subject: Re: route cache DoS testing and softirqs

From: Srivatsa Vaddagiri <[email-masked]>
Date: Tue, 30 Mar 2004 11:05:15 +0530

On Tue, Mar 30, 2004 at 10:36:14AM +0530, Srivatsa Vaddagiri wrote:
> kthread_stop does:
> 
> 	1. kthread_stop_info.k = k;
>         2. wake_up_process(k);
> 
> and if ksoftirqd were to do :
> 
> 	a. while (!kthread_should_stop()) {
>         b.         __set_current_state(TASK_INTERRUPTIBLE);
>         c.         schedule();
>            }
> 
> 
> There is a (narrow) possibility here that a) happens _after_ 1) as well as 
> b) _after_ 2).

hmm .. I meant a) happening _before_ 1) and b) happening _after_ 2) ..

> 
>         a. __set_current_state(TASK_INTERRUPTIBLE);
> 	b. while (!kthread_should_stop()) {
>         c.         schedule();
>         d.         __set_current_state(TASK_INTERRUPTIBLE);
>            }
> 
>         e. __set_current_state(TASK_RUNNING);
> 
> In this case, even if b) happens _after_ 1) and c) _after_ 2), 

Again I meant "even if b) happens _before_ 1) and c) _after_ 2) !!

> schedule simply returns immediately because task's state would have been set 
> to TASK_RUNNING by 2). It goes back to the kthread_should_stop() check and 
> exits!

-- 

Thanks and Regards,
Srivatsa Vaddagiri,
Linux Technology Center,
IBM Software Labs,
Bangalore, INDIA - 560017