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 <okash.khawaja@gmail.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/speakup/main.c b/drivers/staging/speakup/main.c
index 67956e2..56f7be6 100644 (file)
--- a/drivers/staging/speakup/main.c
+++ b/drivers/staging/speakup/main.c
@@ -1376,6 +1376,8 @@ static void reset_highlight_buffers(struct vc_data *);
 
 static int read_all_key;
 
+static int in_keyboard_notifier;
+
 static void start_read_all_timer(struct vc_data *vc, int command);
 
 enum {
@@ -1408,7 +1410,10 @@ static void read_all_doc(struct vc_data *vc)
        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);
@@ -2212,8 +2217,10 @@ static int keyboard_notifier_call(struct notifier_block *nb,
        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
@@ -2225,7 +2232,7 @@ static int keyboard_notifier_call(struct notifier_block *nb,
         */
 
        if (speakup_fake_key_pressed())
-               return ret;
+               goto out;
 
        switch (code) {
        case KBD_KEYCODE:
@@ -2266,6 +2273,8 @@ static int keyboard_notifier_call(struct notifier_block *nb,
                        break;
                }
        }
+out:
+       in_keyboard_notifier = 0;
        return ret;
 }