staging: comedi: wake up async waiters when become non-busy

Wake up all waiters on the comedi subdevice's async wait queue whenever
the subdevice is marked "non-busy".  This happens when an asynchronous
command is cancelled or when a command is terminated and all data has
been read or written.  Note: use `wake_up_interruptible_all()` as we
only use interruptible waits.

Remove the call to `wake_up_interruptible()` from `do_cancel_ioctl()` as
it will call `wake_up_interruptible_all()` indirectly via `do_cancel()`
and `do_become_nonbusy()`.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/comedi_fops.c

@@ -563,12 +563,13 @@ static void do_become_nonbusy(struct comedi_device *dev,
 		async->inttrig = NULL;
 		kfree(async->cmd.chanlist);
 		async->cmd.chanlist = NULL;
+		s->busy = NULL;
+		wake_up_interruptible_all(&s->async->wait_head);
 	} else {
 		dev_err(dev->class_dev,
 			"BUG: (?) do_become_nonbusy called with async=NULL\n");
-	}
-
 		s->busy = NULL;
+	}
 }
 
 static int do_cancel(struct comedi_device *dev, struct comedi_subdevice *s)
@@ -1700,7 +1701,6 @@ static int do_cancel_ioctl(struct comedi_device *dev, unsigned int arg,
 		return -EBUSY;
 
 	ret = do_cancel(dev, s);
-	wake_up_interruptible(&s->async->wait_head);
 
 	return ret;
 }