cdc-acm: introduce a cool down

Immediate submission in case of a babbling device can lead
to a busy loop. Introducing a delayed work.

Signed-off-by: Oliver Neukum <[e-mail]>
Cc: stable <[e-mail]>
Tested-by: Jonas Karlsson <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/class/cdc-acm.c

···
 
 exit:
 	retval = usb_submit_urb(urb, GFP_ATOMIC);
-	if (retval && retval != -EPERM)
+	if (retval && retval != -EPERM && retval != -ENODEV)
 		dev_err(&acm->control->dev,
 			"%s - usb_submit_urb failed: %d\n", __func__, retval);
+	else
+		dev_vdbg(&acm->control->dev,
+			"control resubmission terminated %d\n", retval);
 }
 
 static int acm_submit_read_urb(struct acm *acm, int index, gfp_t mem_flags)
···
 			dev_err(&acm->data->dev,
 				"urb %d failed submission with %d\n",
 				index, res);
+		} else {
+			dev_vdbg(&acm->data->dev, "intended failure %d\n", res);
 		}
 		set_bit(index, &acm->read_urbs_free);
 		return res;
···
 	int status = urb->status;
 	bool stopped = false;
 	bool stalled = false;
+	bool cooldown = false;
 
 	dev_vdbg(&acm->data->dev, "got urb %d, len %d, status %d\n",
 		rb->index, urb->actual_length, status);
···
 			__func__, status);
 		stopped = true;
 		break;
+	case -EOVERFLOW:
+	case -EPROTO:
+		dev_dbg(&acm->data->dev,
+			"%s - cooling babbling device\n", __func__);
+		usb_mark_last_busy(acm->dev);
+		set_bit(rb->index, &acm->urbs_in_error_delay);
+		cooldown = true;
+		break;
 	default:
 		dev_dbg(&acm->data->dev,
 			"%s - nonzero urb status received: %d\n",
···
 	 */
 	smp_mb__after_atomic();
 
-	if (stopped || stalled) {
+	if (stopped || stalled || cooldown) {
 		if (stalled)
 			schedule_work(&acm->work);
+		else if (cooldown)
+			schedule_delayed_work(&acm->dwork, HZ / 2);
 		return;
 	}
 
···
 			acm_submit_read_urbs(acm, GFP_KERNEL);
 			clear_bit(EVENT_RX_STALL, &acm->flags);
 		}
+	}
+
+	if (test_and_clear_bit(ACM_ERROR_DELAY, &acm->flags)) {
+		for (i = 0; i < ACM_NR; i++) 
+			if (test_and_clear_bit(i, &acm->urbs_in_error_delay))
+					acm_submit_read_urb(acm, i, GFP_NOIO);
 	}
 
 	if (test_and_clear_bit(EVENT_TTY_WAKEUP, &acm->flags))
···
 	acm->readsize = readsize;
 	acm->rx_buflimit = num_rx_buf;
 	INIT_WORK(&acm->work, acm_softint);
+	INIT_DELAYED_WORK(&acm->dwork, acm_softint);
 	init_waitqueue_head(&acm->wioctl);
 	spin_lock_init(&acm->write_lock);
 	spin_lock_init(&acm->read_lock);
···
 
 	acm_kill_urbs(acm);
 	cancel_work_sync(&acm->work);
+	cancel_delayed_work_sync(&acm->dwork);
 
 	tty_unregister_device(acm_tty_driver, acm->minor);
 
···
 
 	acm_kill_urbs(acm);
 	cancel_work_sync(&acm->work);
+	cancel_delayed_work_sync(&acm->dwork);
+	acm->urbs_in_error_delay = 0;
 
 	return 0;
 }

drivers/usb/class/cdc-acm.h

···
 #		define EVENT_TTY_WAKEUP	0
 #		define EVENT_RX_STALL	1
 #		define ACM_THROTTLED	2
+#		define ACM_ERROR_DELAY	3
+	unsigned long urbs_in_error_delay;		/* these need to be restarted after a delay */
 	struct usb_cdc_line_coding line;		/* bits, stop, parity */
-	struct work_struct work;			/* work queue entry for line discipline waking up */
+	struct work_struct work;			/* work queue entry for various purposes*/
+	struct delayed_work dwork;			/* for cool downs needed in error recovery */
 	unsigned int ctrlin;				/* input control lines (DCD, DSR, RI, break, overruns) */
 	unsigned int ctrlout;				/* output control lines (DTR, RTS) */
 	struct async_icount iocount;			/* counters for control line changes */