Using tq_immediate

[Matthew Wilcox]

If you want to use tq_immediate, here's the current way to do it:

        queue_task(&bcs->tqueue, &tq_immediate);
        mark_bh(IMMEDIATE_BH);

There's about 80 drivers in the tree which do this, FYI.  This sucks,
because it sets up a linkage between task queues and bottom halves.
If you, like I, wish for bottom halves to go away, we're going to have
to change this.  Some people want to eradicate task queues too -- and
while I think this is a fine idea, I can't see it happening in the next
week or so.

My proposal is:

	queue_task(&bcs->tqueue, &tq_immediate);
	wake_immediate_queue();

While this is a little magic (there's no obvious connection between the
two), and it's special-purpose (no equivalent for other task queues),
I think it's an acceptable compromise that doesn't require taking out
all 80 drivers and shooting them.

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