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

[Bernd Walter]

On Fri, Apr 01, 2005 at 11:17:53PM +0200, Hans Petter Selasky wrote:
> On Friday 01 April 2005 21:44, Sebastien B wrote:
> > > 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
> 
> With the existing USB driver you cannot call usbd_abort_pipe() nor 
> usbd_bulk_transfer(), from an interrupt context or callback, because those 
> functions will sleep. You can call usbd_transfer(), if the transfer is not 
> synchronous.

this is not really true.
Under 5.x only fast interrupt handlers are running in interrupt context.
It should be perfectly OK to sleep in a callback function.

> But the panic is a bug, and it might be because the ehci_abort_xfer() function 
> is called from the transfer's timeout function?

Likely something in this line.
AFAIK timer events are directly called from the interrupt handler.

> The solution is to use DELAY() instead of tsleep() and usb_delay_ms().

This is wrong either way - wasting cycles in interrupt context is bad.
IMO the timeout function should trigger a softint doing the real job.
Maybe Ian has an idea about this - he did a lot in respect to timeout
and aborting xfers lately and should be familar with this point.
To be shure it still exists you should verify with latest code.

-- 
B.Walter                   BWCT                http://www.bwct.de
bernd at bwct.de                                  info at bwct.de