Messages in this thread | | | Date | Fri, 11 Jul 2014 14:05:42 +0200 | From | Olivier Sobrie <> | Subject | Re: [PATCH 2/2] hso: fix deadlock when receiving bursts of data |
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On Fri, Jul 11, 2014 at 09:28:47AM +0000, David Laight wrote: > From: Olivier Sobrie Olivier Sobrie > > Hi Alan and Davids, > > > > On Thu, Jul 10, 2014 at 04:50:03PM +0100, One Thousand Gnomes wrote: > > > On Thu, 10 Jul 2014 14:37:37 +0000 > > > David Laight <David.Laight@ACULAB.COM> wrote: > > > > > > > From: Olivier Sobrie > > > > ... > > > > > The function put_rxbuf_data() is called from the urb completion handler. > > > > > It puts the data of the urb transfer in the tty buffer with > > > > > tty_insert_flip_string_flags() and schedules a work queue in order to > > > > > push the data to the ldisc. > > > > > Problem is that we are in a urb completion handler so we can't wait > > > > > until there is room in the tty buffer. > > > > > > The tty provides the input queue, if the queue is full then just chuck > > > the data in the bitbucket. hso is trying to be far too clever. > > > > > > If hso is fast enough that the buffering isn't sufficient on the tty side > > > then we need to fix the tty buffer size. > > > > Ok I'll adapt the patch to drop the data that can't be put in the tty > > buffer. I test this and resend a new patch. > > If you are going to drop data, then ideally you want to discard entire ppp > packets. Depending on exactly how the interface works it might be that > urb are likely to contain complete packets.
Indeed, urbs contains complete ppp packets. I see that the first and last byte are equal to 0x7e.
> > So discarding entire urb might work better than discarding a few bytes. > (But don't even think of scanning the data stream in the usb driver - except > for experiments.)
I will check with tty_buffer_request_room() that there is enough room to receive the frame before inserting the data in the tty buffer with tty_insert_flip_string().
-- Olivier
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