lkml.org 
[lkml]   [2003]   [Aug]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: tasklet_kill will always hang for recursive tasklets on a UP
Sorry, I forgot to mention my kernel version.
It is 2.14.18-14 (RH-8.0 stock kernel)

Thanx
tomar

On Mon, 25 Aug 2003, Tomar, Nagendra wrote:

> Hi,
> While going thru the code for tasklet_kill(), I cannot figure
> out
> how recursive tasklets (tasklets that schedule themselves from within
> their tasklet handler) can be killed by this function. To me it looks
> that
> tasklet_kill will never complete for such tasklets.
>
> void tasklet_kill(struct tasklet_struct *t)
> {
> ...
> ...
> while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
> current->state = TASK_RUNNING;
> do
> sys_sched_yield();
> while (test_bit(TASKLET_STATE_SCHED, &t->state));
> }
> ...
> ...
> }
>
> The above while loop will only exit if TASKLET_STATE_SCHED is not set
> (tasklet is not scheduled).
> Now if we see tasklet_action
>
> static void tasklet_action(struct softirq_action *a)
> {
> ...
> ...
> if (!atomic_read(&t->count)) {
> --> TASKLET_STATE_SCHED is set here
> if(!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
> BUG();
> t->func(t->data);
> --> if we schedule the tasklet inside its handler,
> --> TASKLET_STATE_SCHED will be set here also
> tasklet_unlock(t);
> continue;
> }
> ...
> ...
> }
>
> The only small window when TASKLET_STATE_SCHED is not set is between the
>
> time when test_and_clear_bit above clears it and by the time the tasklet
>
> handler again calls tasklet_schedule(). But since tasklet_kill is called
>
> from user context the while loop in tasklet_kill checking for
> TASKLET_STATE_SCHED to be cleared cannot interleave between the above
> two
> lines in tasklet_action and hence tasklet_kill will never come out of
> the
> while loop.
> This is true only for UP machines.
>
> Pleae point me out if I am missing something.
>
> Thanx
> tomar
>
>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel"
> in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
>

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:48    [from the cache]
©2003-2011 Jasper Spaans