Re: a few usb issues related to edge cases

on 21/12/2011 18:38 Hans Petter Selasky said the following:
> On Wednesday 21 December 2011 12:29:49 Andriy Gapon wrote:
>> on 20/12/2011 14:25 Andriy Gapon said the following:
>>> I just wanted to draw your attention to the fact that obtaining any locks
>>> in the kdb context (or USB polling code in general, even) is not a good
>>> idea. Chances of getting into trouble on those locks are probably quite
>>> moderate or even low, but they do exist.  I am not sure if you are
>>> getting any bug reports about such troubles :-)  Regular users probably
>>> do not use kdb too often and a panic for them is just a "crash", so they
>>> likely do not expect anything usable/debuggable after that :-)
>>
>> Looking some more at the code I just got myself confused as to how the
>> dumping to a umass device could work when the scheduler is stopped.
>> It seems that the umass_command_start -> usbd_transfer_start ->
>> usbd_callback_ss_done_defer functions would always put a transfer request
>> onto a queue and try to wake up a thread to process that queue and the
>> request.  But that's obviously not going to work when the other thread is
>> not going to be run. Have I missed a code path that leads directly to the
>> controller in this context? Thank you for your help.
> 
> Hi,
> 
> Those threads should be polled when calling usbd_transfer_poll(). I.E. the 
> wakeup should be stubbed in the !scheduler_running case.

Ah, that's what I missed!

-- 
Andriy Gapon