speakup-r empty line lockup

[Okash Khawaja]

Yes export-tty.patch on the repo has been updated. Let me know if you get any problems. 

Cheers,
Okash

> On 24 Jun 2017, at 11:12, John Covici <covici at ccs.covici.com> wrote:
> 
> 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