speakup-r empty line lockup

[Okash Khawaja]

Hi,

This looks like the problem you raised previously, the one which was
resolved by calling flush_buffers. Is this happening on ttyUSB?
usb-serial driver doesn't implement flush_buffers method which means
that speakup-r will have this issue until there is flush_buffers in
usb-serial.

Thanks,
Okash

On Mon, Jul 03, 2017 at 05:52:19AM -0400, John Covici wrote:
> I just tested the empty line lockup is  gone, but now speakup-r does
> not work, actually in the file I had, after reading a  number of lines
> when I hit control, the cursor was actually at the end of the file.
> 
> Thanks for working on this one.
> 
> On Sat, 24 Jun 2017 05:06:45 -0400,
> Okash Khawaja wrote:
> > 
> > Hi,
> > 
> > The lockup when running speakup-r at start of an empty line occurs
> > because simulated key press is generated (using speakup_fake_down_arrow)
> > from context of keyboard_notifier_call callback which is called in
> > interrupt context. The simulated keypress leads to
> > keybaord_notifier_call to be trigerred again from the same context
> > leading to the lockup. The exact cause could be priority inversion where
> > simulated keypress cannot be processed because there is a real keyboard
> > interrupt already being processed (the one from which simulated keypress
> > was triggered), hence causing a deadlock. Please share your thoughts on
> > this. Here is the call chain.
> > 
> > (speakup-r) --> keyboard_notifier_call --> speakup_key --> do_spkup -->
> > read_all_doc --> get_sentence_buf [which returns -1 because of empty
> > line] --> kbd_fakekey2(RA_DOWN_ARROW) --> speakup_fake_down_arrow
> > 
> > The following patch resolves this by not simulating the keypress inside
> > keyboard notifier callback but instead delegating it to cursor_timer. In
> > the above chain, when get_sentence_buf returns -1, this patch starts
> > timer and passes RA_DOWN_ARROW as argument. When timer handler runs and
> > sees RA_DOWN_ARROW, it will then call kbd_fakekey2(RA_DOWN_ARROW) which
> > will correctly simulate the keypress inside timer context. I've tested
> > this succesfully.
> > 
> > It's the first time I've worked on this side of the code so please
> > review carefully :)
> > 
> > Finally, I have updated the test repo on github so you can test from
> > there.
> > 
> > Thanks,
> > Okash
> > 
> > ---
> >  drivers/staging/speakup/main.c |    3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > --- a/drivers/staging/speakup/main.c
> > +++ b/drivers/staging/speakup/main.c
> > @@ -1408,7 +1408,8 @@ static void read_all_doc(struct vc_data
> >  	cursor_track = read_all_mode;
> >  	spk_reset_index_count(0);
> >  	if (get_sentence_buf(vc, 0) == -1) {
> > -		kbd_fakekey2(vc, RA_DOWN_ARROW);
> > +		del_timer(&cursor_timer);
> > +		start_read_all_timer(vc, RA_DOWN_ARROW);
> >  	} else {
> >  		say_sentence_num(0, 0);
> >  		synth_insert_next_index(0);
> 
> -- 
> Your life is like a penny.  You're going to lose it.  The question is:
> How do
> you spend it?
> 
>          John Covici
>          covici at ccs.covici.com