HID: wiimote: fix FF deadlock

The input core has an internal spinlock that is acquired during event
injection via input_event() and friends but also held during FF callbacks.
That means, there is no way to share a lock between event-injection and FF
handling. Unfortunately, this is what is required for wiimote state
tracking and what we do with state.lock and input->lock.

This deadlock can be triggered when using continuous data reporting and FF
on a wiimote device at the same time. I takes me at least 30m of
stress-testing to trigger it but users reported considerably shorter
times (http://bpaste.net/show/132504/) when using some gaming-console
emulators.

The real problem is that we have two copies of internal state, one in the
wiimote objects and the other in the input device. As the input-lock is
not supposed to be accessed from outside of input-core, we have no other
chance than offloading FF handling into a worker. This actually works
pretty nice and also allows to implictly merge fast rumble changes into a
single request.

Due to the 3-layered workers (rumble+queue+l2cap) this might reduce FF
responsiveness. Initial tests were fine so lets fix the race first and if
it turns out to be too slow we can always handle FF out-of-band and skip
the queue-worker.

Cc: <stable@vger.kernel.org> # 3.11+
Reported-by: Thomas Schneider
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

diff --git a/drivers/hid/hid-wiimote-modules.c b/drivers/hid/hid-wiimote-modules.c
index 2e7d644..71adf9e 100644 (file)
--- a/drivers/hid/hid-wiimote-modules.c
+++ b/drivers/hid/hid-wiimote-modules.c
@@ -119,12 +119,22 @@ static const struct wiimod_ops wiimod_keys = {
  * the rumble motor, this flag shouldn't be set.
  */
 
+/* used by wiimod_rumble and wiipro_rumble */
+static void wiimod_rumble_worker(struct work_struct *work)
+{
+       struct wiimote_data *wdata = container_of(work, struct wiimote_data,
+                                                 rumble_worker);
+
+       spin_lock_irq(&wdata->state.lock);
+       wiiproto_req_rumble(wdata, wdata->state.cache_rumble);
+       spin_unlock_irq(&wdata->state.lock);
+}
+
 static int wiimod_rumble_play(struct input_dev *dev, void *data,
                              struct ff_effect *eff)
 {
        struct wiimote_data *wdata = input_get_drvdata(dev);
        __u8 value;
-       unsigned long flags;
 
        /*
         * The wiimote supports only a single rumble motor so if any magnitude
@@ -137,9 +147,10 @@ static int wiimod_rumble_play(struct input_dev *dev, void *data,
        else
                value = 0;
 
-       spin_lock_irqsave(&wdata->state.lock, flags);
-       wiiproto_req_rumble(wdata, value);
-       spin_unlock_irqrestore(&wdata->state.lock, flags);
+       /* Locking state.lock here might deadlock with input_event() calls.
+        * schedule_work acts as barrier. Merging multiple changes is fine. */
+       wdata->state.cache_rumble = value;
+       schedule_work(&wdata->rumble_worker);
 
        return 0;
 }
@@ -147,6 +158,8 @@ static int wiimod_rumble_play(struct input_dev *dev, void *data,
 static int wiimod_rumble_probe(const struct wiimod_ops *ops,
                               struct wiimote_data *wdata)
 {
+       INIT_WORK(&wdata->rumble_worker, wiimod_rumble_worker);
+
        set_bit(FF_RUMBLE, wdata->input->ffbit);
        if (input_ff_create_memless(wdata->input, NULL, wiimod_rumble_play))
                return -ENOMEM;
@@ -159,6 +172,8 @@ static void wiimod_rumble_remove(const struct wiimod_ops *ops,
 {
        unsigned long flags;
 
+       cancel_work_sync(&wdata->rumble_worker);
+
        spin_lock_irqsave(&wdata->state.lock, flags);
        wiiproto_req_rumble(wdata, 0);
        spin_unlock_irqrestore(&wdata->state.lock, flags);
@@ -1731,7 +1746,6 @@ static int wiimod_pro_play(struct input_dev *dev, void *data,
 {
        struct wiimote_data *wdata = input_get_drvdata(dev);
        __u8 value;
-       unsigned long flags;
 
        /*
         * The wiimote supports only a single rumble motor so if any magnitude
@@ -1744,9 +1758,10 @@ static int wiimod_pro_play(struct input_dev *dev, void *data,
        else
                value = 0;
 
-       spin_lock_irqsave(&wdata->state.lock, flags);
-       wiiproto_req_rumble(wdata, value);
-       spin_unlock_irqrestore(&wdata->state.lock, flags);
+       /* Locking state.lock here might deadlock with input_event() calls.
+        * schedule_work acts as barrier. Merging multiple changes is fine. */
+       wdata->state.cache_rumble = value;
+       schedule_work(&wdata->rumble_worker);
 
        return 0;
 }
@@ -1756,6 +1771,8 @@ static int wiimod_pro_probe(const struct wiimod_ops *ops,
 {
        int ret, i;
 
+       INIT_WORK(&wdata->rumble_worker, wiimod_rumble_worker);
+
        wdata->extension.input = input_allocate_device();
        if (!wdata->extension.input)
                return -ENOMEM;
@@ -1817,12 +1834,13 @@ static void wiimod_pro_remove(const struct wiimod_ops *ops,
        if (!wdata->extension.input)
                return;
 
+       input_unregister_device(wdata->extension.input);
+       wdata->extension.input = NULL;
+       cancel_work_sync(&wdata->rumble_worker);
+
        spin_lock_irqsave(&wdata->state.lock, flags);
        wiiproto_req_rumble(wdata, 0);
        spin_unlock_irqrestore(&wdata->state.lock, flags);
-
-       input_unregister_device(wdata->extension.input);
-       wdata->extension.input = NULL;
 }
 
 static const struct wiimod_ops wiimod_pro = {

diff --git a/drivers/hid/hid-wiimote.h b/drivers/hid/hid-wiimote.h
index f1474f3..75db0c4 100644 (file)
--- a/drivers/hid/hid-wiimote.h
+++ b/drivers/hid/hid-wiimote.h
@@ -133,13 +133,15 @@ struct wiimote_state {
        __u8 *cmd_read_buf;
        __u8 cmd_read_size;
 
-       /* calibration data */
+       /* calibration/cache data */
        __u16 calib_bboard[4][3];
+       __u8 cache_rumble;
 };
 
 struct wiimote_data {
        struct hid_device *hdev;
        struct input_dev *input;
+       struct work_struct rumble_worker;
        struct led_classdev *leds[4];
        struct input_dev *accel;
        struct input_dev *ir;