Re: workqueue code needing preemption disabled

[Steven Rostedt]

On Mon, 2013-03-18 at 12:23 -0400, Steven Rostedt wrote:

> > Maybe I'm confused but I can't really see how the above would be a
> > problem to workqueue in itself.  Both rq->lock and gcwq->lock are
> > irq-safe, so spin_lock() not disabling preemption shouldn't be a
> > problem.  Are CPU hotplug operations involved?
> 
> No CPU hotplug is involved here. But I will note that gcwq->lock in -rt
> is not irq -safe. That is, in rt the spin_lock_irq(&gcwq->lock) really
> becomes a special "mutex_lock(&gcwq->lock)".

IOW, what can happen in -rt here is:

	spin_lock_irq(&gcwq->lock);
	[...]
	<interrupt>
		-> preempt_schedule();
		   schedule();
		   try_to_wake_up_local();

	[...]
	spin_unlock_irq(&gcwq->lock);

Again, with -rt, spin_lock_irq() does not prevent interrupts nor
preemption.

-- Steve


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