Re: [PATCH] hid: usbhid: fix possible deadlock in __usbhid_submit_report

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On Sat, Apr 21, 2012 at 6:25 PM, Oliver Neukum <oliver@xxxxxxxxxx> wrote:
> Am Samstag, 21. April 2012, 02:37:35 schrieb Alan Stern:
>> On Fri, 20 Apr 2012, Oliver Neukum wrote:
>>
>> > As I said, I'd very much appreciate sane semantics for usb_unlink_urb().
>>
>> Aside from the practicality issue of altering a large number of
>> existing drivers, changing the semantics the way you want would be
>> difficult because it would force the HCDs to defer some giveback
>> operations to a bottom half or timer routine.
>
> Or a work queue, which would have to be dedicated to avoid deadlocks
> with storage.
>
>> Think about what happens if the URB being unlinked hasn't been
>> presented to the hardware yet.  Once it has been removed from the HCD's
>> internal lists, there's no reason not to give it back right away.  And
>> there's no natural time to give it back later.
>
> Now. The question is not when, but from which context.
> The context should be uniform, so that the requirements
> for locking should also be uniform.

How about always scheduling a tasklet to run what usb_unlink_urb does?
just implement usb_unlink_urb as something like
tasklet_schedule(unlink_tasklet).

Then we can have a uniform lock requirement and no changes are involved
on host controller drivers.


Thanks,
--
Ming Lei
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