USB: gadget: f_hid: avoid crashes and log spam

Disconnecting and reconnecting the USB cable can lead to crashes and a
variety of kernel log spam. Try to fix or minimise both.

See: #3870

Signed-off-by: Phil Elwell <phil@raspberrypi.com>

drivers/usb/gadget/function/f_hid.c

@@ -338,6 +338,11 @@ static ssize_t f_hidg_write(struct file *file, const char __user *buffer,
 
 	spin_lock_irqsave(&hidg->write_spinlock, flags);
 
+	if (!hidg->req) {
+		spin_unlock_irqrestore(&hidg->write_spinlock, flags);
+		return -ESHUTDOWN;
+	}
+
 #define WRITE_COND (!hidg->write_pending)
 try_again:
 	/* write queue */
@@ -358,7 +363,13 @@ static ssize_t f_hidg_write(struct file *file, const char __user *buffer,
 	count  = min_t(unsigned, count, hidg->report_length);
 
 	spin_unlock_irqrestore(&hidg->write_spinlock, flags);
-	status = copy_from_user(req->buf, buffer, count);
+	if (req) {
+		status = copy_from_user(req->buf, buffer, count);
+	} else {
+		ERROR(hidg->func.config->cdev, "hidg->req is NULL\n");
+		status = -ESHUTDOWN;
+		goto release_write_pending;
+	}
 
 	if (status != 0) {
 		ERROR(hidg->func.config->cdev,
@@ -387,10 +398,13 @@ static ssize_t f_hidg_write(struct file *file, const char __user *buffer,
 
 	spin_unlock_irqrestore(&hidg->write_spinlock, flags);
 
+	if (!hidg->in_ep->enabled) {
+		ERROR(hidg->func.config->cdev, "in_ep is disabled\n");
+		status = -ESHUTDOWN;
+		goto release_write_pending;
+	}
 	status = usb_ep_queue(hidg->in_ep, req, GFP_ATOMIC);
 	if (status < 0) {
-		ERROR(hidg->func.config->cdev,
-			"usb_ep_queue error on int endpoint %zd\n", status);
 		goto release_write_pending;
 	} else {
 		status = count;