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Re: route cache DoS testing and softirqs

To: Andrea Arcangeli <andrea@xxxxxxx>
Subject: Re: route cache DoS testing and softirqs
From: Srivatsa Vaddagiri <vatsa@xxxxxxxxxx>
Date: Tue, 30 Mar 2004 11:05:15 +0530
Cc: Dipankar Sarma <dipankar@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxx, Robert Olsson <Robert.Olsson@xxxxxxxxxxx>, "Paul E. McKenney" <paulmck@xxxxxxxxxx>, Dave Miller <davem@xxxxxxxxxx>, Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxx>, rusty@xxxxxxxxxxx
In-reply-to: <20040330050614.GA4669@xxxxxxxxxx>
References: <20040329184550.GA4540@xxxxxxxxxx> <20040329222926.GF3808@xxxxxxxxxxxxxxxxx> <20040330050614.GA4669@xxxxxxxxxx>
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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

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