Re: puting task to TASK_INTERRUPTIBLE before adding it to an waitqueue

[Mike Galbraith]

On Fri, 2006-03-17 at 00:31 +0200, Yitzchak Eidus wrote:
> the function worker_thread in kernel 2.6.15.6  first put the task to
> TASK_INTERRUPTIBLE and only then add itself to an wait queue:
> 	set_current_state(TASK_INTERRUPTIBLE);
> 	while (!kthread_should_stop()) {
> 		add_wait_queue(&cwq->more_work, &wait);

See dusty old archives...

http://www.ussg.iu.edu/hypermail/linux/kernel/9712.2/0545.html

<quote>
Anyway, the basic race-free wait loop looks like this (there are
variations, but this is one of the basic versions that you find in
various places):


if (should_wait_condition) {
add_wait_queue(..);
repeat:
current->state = TASK_UNINTERRUPTIBLE;
if (should_wait_condition) {
schedule();
goto repeat;
}
remove_wait_queue(..);
current->state = TASK_RUNNING;
}


There are only two important rules:
- you have to add yourself to the wait queue _before_ testing for the
condition.
- you have to mark yourself asleep _before_ testing for the condition.

</quote>

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