Quoting David Howells (dhowells@xxxxxxxxxx):
> David Howells <dhowells@xxxxxxxxxx> wrote:
>
> > I guess I need to stick a comment in slow_work_enqueue() to detail this,
> > though the comments in slow_work_execute() do talk about it.
>
> How about this:
>
> diff --git a/kernel/slow-work.c b/kernel/slow-work.c
> index f638f36..adf9b78 100644
> --- a/kernel/slow-work.c
> +++ b/kernel/slow-work.c
> @@ -195,12 +195,32 @@ int slow_work_enqueue(struct slow_work *work)
> BUG_ON(!work->ops);
> BUG_ON(!work->ops->get_ref);
>
> + /* when honouring an enqueue request, we only promise that we will run
> + * the work function in the future; we do not promise to run it once
> + * per enqueue request
That, there, is precisely what i needed to hear :)
> + * we use the PENDING bit to merge together repeat requests without
> + * having to disable IRQs and take the spinlock, whilst still
> + * maintaining our promise
> + */
> if (!test_and_set_bit_lock(SLOW_WORK_PENDING, &work->flags)) {
> spin_lock_irqsave(&slow_work_queue_lock, flags);
>
> + /* we promise that we will not attempt to execute the work
> + * function in more than one thread simultaneously
> + *
> + * this, however, leaves us with a problem if we're asked to
> + * enqueue the work whilst someone is executing the work
> + * function as simply queueing the work immediately means that
> + * another thread may try executing it whilst it is already
> + * under execution
> + *
> + * to deal with this, we set the ENQ_DEFERRED bit instead of
> + * enqueueing, and the thread currently executing the work
> + * function will enqueue the work item when the work function
> + * returns and it has cleared the EXECUTING bit
> + */
> if (test_bit(SLOW_WORK_EXECUTING, &work->flags)) {
> - /* can't queue lest we cause multiple threads to try
> - * executing this item, so defer for later */
> set_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags);
> } else {
> if (work->ops->get_ref(work) < 0)
>
> David
thanks,
-serge
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