speakup-r empty line lockup

[John Covici]

Thanks a lot, I will definitely test this -- do I need a new
export.patch as well?

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