Re: [PATCH 2/2] hso: fix deadlock when receiving bursts of data

Hi David,

On Mon, Jul 07, 2014 at 09:13:53AM +0000, David Laight wrote:

From: Olivier Sobrie

quoted

When the module sends bursts of data, sometimes a deadlock happens in
the hso driver when the tty buffer doesn't get the chance to be flushed
quickly enough.

To avoid this, first, we remove the endless while loop in
put_rx_bufdata() which is the root cause of the deadlock.
Secondly, when there is no room anymore in the tty buffer, we set up a
timer of 100 msecs to give a chance to the upper layer to flush the tty
buffer and make room for new data.

What is the timer for?
You need to get the sending code woken up by the urb completion.

In put_rxbuf_data() (which can be called under irq disabled),
tty_flip_buffer_push() is called and schedules a push of the tty buffer.
When the buffer is full, I give some time to the above layer in order
to flush it.
The timer is used to recall put_rxbuf_data_and_resubmit_bulk_urb()
later in order to read the remaining data stored in
"urb->transfer_buffer" and then to resubmit the urb to receive more data
from the gsm module.
I don't understand what you mean by "getting the sending code woken up".
Calling tty_port_tty_wakeup()?? We are in the receive path...

Thanks,

-- 
Olivier