From 970679b04c4b2ae8aaede98e214449eb3e6e6b06 Mon Sep 17 00:00:00 2001 From: Ian Abbott Date: Mon, 12 Oct 2015 17:21:20 +0100 Subject: staging: comedi: remain busy until read end-of-file If a COMEDI subdevice is busy handling an asynchronous command in the "read" direction, then after the command has terminated itself, the "read" file operation handler, `comedi_read()` should keep the subdevice busy until all available data has been read and it has returned 0 to indicate an "end-of-file" condition. Currently, it has a bug where it can mark the subdevice as non-busy even when returning a non-zero count. The bug is slightly hidden because the next "read" will return 0 because the subdevice is no longer busy. Fix it by checking the return count is 0 before deciding to mark the subdevice as non-busy. The call to `comedi_is_subdevice_idle()` is superfluous as the `become_nonbusy` variable will have been set to `true` when considering becoming non-busy. Strictly speaking, checking the return count is superfluous too, as `become_nonbusy` doesn't get set to `true` unless the count is 0, but check the return count anyway to make the intention clearer. Signed-off-by: Ian Abbott Reviewed-by: H Hartley Sweeten Signed-off-by: Greg Kroah-Hartman --- drivers/staging/comedi/comedi_fops.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/staging/comedi/comedi_fops.c') diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c index fe25287c5688..bb2e0ae0e052 100644 --- a/drivers/staging/comedi/comedi_fops.c +++ b/drivers/staging/comedi/comedi_fops.c @@ -2551,7 +2551,7 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes, } remove_wait_queue(&async->wait_head, &wait); set_current_state(TASK_RUNNING); - if (become_nonbusy || comedi_is_subdevice_idle(s)) { + if (become_nonbusy && count == 0) { struct comedi_subdevice *new_s; /* -- cgit v1.2.3-55-g7522