panic: uhci_abort_xfer: not in process context (was Re: uplcom / ucom problems on RELENG_5)

[Sebastien B]

> When one is designing a driver, it is very convenient if USB-transfers can
> be stopped/started from the callback of another USB-transfer.
I have run exactly into the same trouble by calling usbd_bulk_transfer() from 
a software interrupt handler (scheduled to run from the context of the start 
procedure of a network interface in order to send packets). The kernel panics 
with "ehci_abort_xfer: not in process context" a few while after the 
transfer. Is it the same problem ? Is a software interrupt handler unsuitable 
for the abort xfer function ? How can I fix it, by using a task queue instead 
of a software interrupt handler ?
Regards,
Sebastien