staging: speakup: fix speakup-r empty line lockup

When cursor is at beginning of an empty or whitespace-only line and
speakup-r typed, kernel locks up. This happens because deadlock of in
input_event function over dev->event_lock, as demonstrated by lockdep
logs. The reason for that is speakup simulates a down arrow - because
cursor is at an empty line - while inside key press notifier handler
which is ultimately triggered from input_event function. The simulated
key press leads to input_event being called again, this time under its
own context. So the spinlock is dev->event_lock is acquired while still
being held.

This patch ensures that key press is not simulated from inside key press
notifier handler. Instead it delegates to cursor_timer. It starts the
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.

When not inside key press notifier callback, the behaviour will remain
the same as before this patch.

Signed-off-by: Okash Khawaja <[e-mail]>
Reviewed-by: Samuel Thibault <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/speakup/main.c

···
 
 static int read_all_key;
 
+static int in_keyboard_notifier;
+
 static void start_read_all_timer(struct vc_data *vc, int command);
 
 enum {
···
 	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);
+		if (!in_keyboard_notifier)
+			speakup_fake_down_arrow();
+		start_read_all_timer(vc, RA_DOWN_ARROW);
 	} else {
 		say_sentence_num(0, 0);
 		synth_insert_next_index(0);
···
 	int ret = NOTIFY_OK;
 	static int keycode;	/* to hold the current keycode */
 
+	in_keyboard_notifier = 1;
+
 	if (vc->vc_mode == KD_GRAPHICS)
-		return ret;
+		goto out;
 
 	/*
 	 * First, determine whether we are handling a fake keypress on
···
 	 */
 
 	if (speakup_fake_key_pressed())
-		return ret;
+		goto out;
 
 	switch (code) {
 	case KBD_KEYCODE:
···
 			break;
 		}
 	}
+out:
+	in_keyboard_notifier = 0;
 	return ret;
 }