[PATCH v3 10/12] HID: logitech-hidpp: Fix connect event race

[Hans de Goede <hdegoede@xxxxxxxxxx>]

There is a connect event race in hidpp_probe() in these 2 lines:

	connected = hidpp_root_get_protocol_version(hidpp) == 0;
	atomic_set(&hidpp->connected, connected);

Specifically the following can happen:

1. This line from hidpp_probe() is executed:
	connected = hidpp_root_get_protocol_version(hidpp) == 0;
   and sets connected to false;

2. A connect-event packet is received and does:
	atomic_set(&hidpp->connected, true);

3. The next line from hidpp_probe() is executed:
	atomic_set(&hidpp->connected, connected);
   and sets the atomic_t back to 0 again.

4. hidpp_connect_event() runs and sees the connected device
   as disconnected because of this.

To fix this make hidpp_connect_event() query the connection status
of the device itself instead of having it rely on possibly stale
data cached in struct hidpp_device.

This series has been tested on the following devices:
Logitech Bluetooth Laser Travel Mouse (bluetooth, HID++ 1.0)
Logitech M720 Triathlon (bluetooth, HID++ 4.5)
Logitech M720 Triathlon (unifying, HID++ 4.5)
Logitech K400 Pro (unifying, HID++ 4.1)
Logitech K270 (eQUAD nano Lite, HID++ 2.0)
Logitech M185 (eQUAD nano Lite, HID++ 4.5)
Logitech LX501 keyboard (27 Mhz, HID++ builtin scroll-wheel, HID++ 1.0)
Logitech M-RAZ105 mouse (27 Mhz, HID++ extra mouse buttons, HID++ 1.0)

Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
---
 drivers/hid/hid-logitech-hidpp.c | 25 +++++--------------------
 1 file changed, 5 insertions(+), 20 deletions(-)

diff --git a/drivers/hid/hid-logitech-hidpp.c b/drivers/hid/hid-logitech-hidpp.c
index e945e4e8180f..4793a3236f17 100644
--- a/drivers/hid/hid-logitech-hidpp.c
+++ b/drivers/hid/hid-logitech-hidpp.c
@@ -194,7 +194,6 @@ struct hidpp_device {
 
 	struct work_struct work;
 	struct kfifo delayed_work_fifo;
-	atomic_t connected;
 	struct input_dev *delayed_input;
 
 	unsigned long quirks;
@@ -3893,8 +3892,6 @@ static int hidpp_raw_hidpp_event(struct hidpp_device *hidpp, u8 *data,
 	}
 
 	if (unlikely(hidpp_report_is_connect_event(hidpp, report))) {
-		atomic_set(&hidpp->connected,
-				!(report->rap.params[0] & (1 << 6)));
 		if (schedule_work(&hidpp->work) == 0)
 			dbg_hid("%s: connect event already queued\n", __func__);
 		return 1;
@@ -4189,12 +4186,14 @@ static struct input_dev *hidpp_allocate_input(struct hid_device *hdev)
 static void hidpp_connect_event(struct hidpp_device *hidpp)
 {
 	struct hid_device *hdev = hidpp->hid_dev;
-	int ret = 0;
-	bool connected = atomic_read(&hidpp->connected);
 	struct input_dev *input;
 	char *name, *devm_name;
+	int ret;
 
-	if (!connected) {
+	/* Get device version to check if it is connected */
+	ret = hidpp_root_get_protocol_version(hidpp);
+	if (ret) {
+		hid_info(hidpp->hid_dev, "Disconnected\n");
 		if (hidpp->battery.ps) {
 			hidpp->battery.online = false;
 			hidpp->battery.status = POWER_SUPPLY_STATUS_UNKNOWN;
@@ -4236,16 +4235,6 @@ static void hidpp_connect_event(struct hidpp_device *hidpp)
 			return;
 	}
 
-	/* the device is already connected, we can ask for its name and
-	 * protocol */
-	if (!hidpp->protocol_major) {
-		ret = hidpp_root_get_protocol_version(hidpp);
-		if (ret) {
-			hid_err(hdev, "Can not get the protocol version.\n");
-			return;
-		}
-	}
-
 	if (hidpp->protocol_major >= 2) {
 		u8 feature_index;
 
@@ -4395,7 +4384,6 @@ static int hidpp_probe(struct hid_device *hdev, const struct hid_device_id *id)
 {
 	struct hidpp_device *hidpp;
 	int ret;
-	bool connected;
 	unsigned int connect_mask = HID_CONNECT_DEFAULT;
 
 	/* report_fixup needs drvdata to be set before we call hid_parse */
@@ -4485,9 +4473,6 @@ static int hidpp_probe(struct hid_device *hdev, const struct hid_device_id *id)
 	else
 		hidpp_non_unifying_init(hidpp);
 
-	connected = hidpp_root_get_protocol_version(hidpp) == 0;
-	atomic_set(&hidpp->connected, connected);
-
 	schedule_work(&hidpp->work);
 	flush_work(&hidpp->work);
 
-- 
2.41.0