fix false disconnect due to a signal sent to the reading process

- In the current implementation, when a signal is sent to the reading process,
  read is cancelled by calling usb_ep_dequeue, which lead into calling
  acc_complete_out with ECONNRESET, but the current logic treats it as
  disconnection, which makes the device inaccessible until cable is actually
  disconnected.
- The fix calls disconnect only when ESHUTDOWN error is passed.
- If data has already arrived while trying cancelling, the data is marked
  as available, and it will be read out on the next read. This is necessary
  as USB bulk is assumed to guarantee no data loss.

Signed-off-by: keunyoung <keunyoung@google.com>

1 files changed, 27 insertions, 5 deletions

diff --git a/drivers/usb/gadget/f_accessory.c b/drivers/usb/gadget/f_accessory.c
index 1df88a6..e9872d1 100644
--- a/drivers/usb/gadget/f_accessory.c
+++ b/drivers/usb/gadget/f_accessory.c
@@ -261,8 +261,10 @@ static void acc_complete_in(struct usb_ep *ep, struct usb_request *req)
 {
 	struct acc_dev *dev = _acc_dev;
 
-	if (req->status != 0)
+	if (req->status == -ESHUTDOWN) {
+		pr_debug("acc_complete_in set disconnected");
 		acc_set_disconnected(dev);
+	}
 
 	req_put(dev, &dev->tx_idle, req);
 
@@ -274,8 +276,10 @@ static void acc_complete_out(struct usb_ep *ep, struct usb_request *req)
 	struct acc_dev *dev = _acc_dev;
 
 	dev->rx_done = 1;
-	if (req->status != 0)
+	if (req->status == -ESHUTDOWN) {
+		pr_debug("acc_complete_out set disconnected");
 		acc_set_disconnected(dev);
+	}
 
 	wake_up(&dev->read_wq);
 }
@@ -557,8 +561,10 @@ static ssize_t acc_read(struct file *fp, char __user *buf,
 
 	pr_debug("acc_read(%d)\n", count);
 
-	if (dev->disconnected)
+	if (dev->disconnected) {
+		pr_debug("acc_read disconnected");
 		return -ENODEV;
+	}
 
 	if (count > BULK_BUFFER_SIZE)
 		count = BULK_BUFFER_SIZE;
@@ -571,6 +577,12 @@ static ssize_t acc_read(struct file *fp, char __user *buf,
 		goto done;
 	}
 
+	if (dev->rx_done) {
+		// last req cancelled. try to get it.
+		req = dev->rx_req[0];
+		goto copy_data;
+	}
+
 requeue_req:
 	/* queue a request */
 	req = dev->rx_req[0];
@@ -588,9 +600,17 @@ requeue_req:
 	ret = wait_event_interruptible(dev->read_wq, dev->rx_done);
 	if (ret < 0) {
 		r = ret;
-		usb_ep_dequeue(dev->ep_out, req);
+		ret = usb_ep_dequeue(dev->ep_out, req);
+		if (ret != 0) {
+			// cancel failed. There can be a data already received.
+			// it will be retrieved in the next read.
+			pr_debug("acc_read: cancelling failed %d", ret);
+		}
 		goto done;
 	}
+
+copy_data:
+	dev->rx_done = 0;
 	if (dev->online) {
 		/* If we got a 0-len packet, throw it back and try again. */
 		if (req->actual == 0)
@@ -619,8 +639,10 @@ static ssize_t acc_write(struct file *fp, const char __user *buf,
 
 	pr_debug("acc_write(%d)\n", count);
 
-	if (!dev->online || dev->disconnected)
+	if (!dev->online || dev->disconnected) {
+		pr_debug("acc_write disconnected or not online");
 		return -ENODEV;
+	}
 
 	while (count > 0) {
 		if (!dev->online) {