[RFC PATCH 0/4] USB: HCD/EHCI: giveback of URB in tasklet context

Oliver Neukum oliver at neukum.org
Tue Jun 11 06:51:41 EDT 2013

On Tuesday 11 June 2013 17:27:28 Ming Lei wrote:
> On Tue, Jun 11, 2013 at 4:49 PM, Oliver Neukum <oliver at neukum.org> wrote:
> > On Tuesday 11 June 2013 16:14:25 Ming Lei wrote:

> > The driver itself may have submitted a timer and race against it.
> > What locking do you need in complete() and a timer to lock against
> > each other?
> Good catch.
> The problem will come if only spin_lock() is called inside complete(),
> I will check main USB drivers in tree to see if there is such use case.

All network drivers race against timeout. I think they just unlink the URB,
but there's a lot of them.

> > But it makes no sense to go to a tasklet when you are already in task context.
> > In those cases you need to do something, essentially blocking the tasklet.
> At least now, always doing complete() in tasklet handler can simplify
> implementation since these cases aren't in hot path.

Well, I am afraid this is not simply the case. These cases are partially
synchronous. For example you need to make sure all calls to complete()
are finished before you disconnect a HCD itself. The same applies to a device
being disconnected.

It the same area, what happens if an URB is unlinked between the irq handler
and the tasklet?


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