staging: comedi: comedi_fops: always clear events

`comedi_event()` is called from low-level drivers to handle asynchronous
command event flags that are stored in `s->async->events` for subdevice
`s`.  It normally clears the event flags as well.  As a safety check, it
does nothing if no asynchronous command is running, but it leaves
`s->async->events` unchanged in this case.  For additional safety,
change it to always clear the event flags to avoid leaving stale event
flags set when another asynchronous command is set up.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/comedi_fops.c

@@ -2648,18 +2648,20 @@ void comedi_event(struct comedi_device *dev, struct comedi_subdevice *s)
 	struct comedi_async *async = s->async;
 	unsigned runflags = 0;
 	unsigned runflags_mask = 0;
+	unsigned int events = async->events;
 
+	async->events = 0;
 	if (!comedi_is_subdevice_running(s))
 		return;
 
-	if (async->events & COMEDI_CB_CANCEL_MASK)
+	if (events & COMEDI_CB_CANCEL_MASK)
 		runflags_mask |= COMEDI_SRF_RUNNING;
 
 	/*
 	 * Remember if an error event has occurred, so an error
 	 * can be returned the next time the user does a read().
 	 */
-	if (async->events & COMEDI_CB_ERROR_MASK) {
+	if (events & COMEDI_CB_ERROR_MASK) {
 		runflags_mask |= COMEDI_SRF_ERROR;
 		runflags |= COMEDI_SRF_ERROR;
 	}
@@ -2671,14 +2673,13 @@ void comedi_event(struct comedi_device *dev, struct comedi_subdevice *s)
 		comedi_update_subdevice_runflags(s, runflags_mask, runflags);
 	}
 
-	if (async->cb_mask & async->events) {
+	if (async->cb_mask & events) {
 		wake_up_interruptible(&async->wait_head);
 		if (s->subdev_flags & SDF_CMD_READ)
 			kill_fasync(&dev->async_queue, SIGIO, POLL_IN);
 		if (s->subdev_flags & SDF_CMD_WRITE)
 			kill_fasync(&dev->async_queue, SIGIO, POLL_OUT);
 	}
-	async->events = 0;
 }
 EXPORT_SYMBOL_GPL(comedi_event);