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[PATCH 5/6] staging: comedi: check command started by file being polled

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Currently, the "poll" file operation checks if an asynchronous "read"
(or "write" command is active on the "read" (or "write" subdevice, but
does not consider whether the command was started from the file object
being polled.  Since that is the only file object able to read (or
write) data, take it into consideration.

With this change, if no read (or write) command is running on the
subdevice, or it is started by a different file object, the file object
is marked as readable (or writeable) regardless, but the read (or write)
file operation will return an error.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
---
 drivers/staging/comedi/comedi_fops.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 4793e30..07bb197 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -2275,7 +2275,7 @@ static unsigned int comedi_poll(struct file *file, poll_table *wait)
 	s_read = s;
 	if (s && s->async) {
 		poll_wait(file, &s->async->wait_head, wait);
-		if (!s->busy || !comedi_is_subdevice_running(s) ||
+		if (s->busy != file || !comedi_is_subdevice_running(s) ||
 		    (s->async->cmd.flags & CMDF_WRITE) ||
 		    comedi_buf_read_n_available(s) > 0)
 			mask |= POLLIN | POLLRDNORM;
@@ -2287,7 +2287,7 @@ static unsigned int comedi_poll(struct file *file, poll_table *wait)
 
 		if (s != s_read)
 			poll_wait(file, &s->async->wait_head, wait);
-		if (!s->busy || !comedi_is_subdevice_running(s) ||
+		if (s->busy != file || !comedi_is_subdevice_running(s) ||
 		    !(s->async->cmd.flags & CMDF_WRITE) ||
 		    comedi_buf_write_n_available(s) >= bps)
 			mask |= POLLOUT | POLLWRNORM;
-- 
2.6.1

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[PATCH 0/6] staging: comedi: fix some minor issues with file poll op Ian Abbott <abbotti@mev.co.uk> - 2015-10-09 13:30 +0200
  [PATCH 5/6] staging: comedi: check command started by file being polled Ian Abbott <abbotti@mev.co.uk> - 2015-10-09 13:30 +0200
  [PATCH 6/6] staging: comedi: don't use mutex when polling file Ian Abbott <abbotti@mev.co.uk> - 2015-10-09 13:30 +0200
    RE: [PATCH 6/6] staging: comedi: don't use mutex when polling file Hartley Sweeten <HartleyS@visionengravers.com> - 2015-10-09 19:30 +0200
  [PATCH 1/6] staging: comedi: don't poll_wait on same subdevice twice Ian Abbott <abbotti@mev.co.uk> - 2015-10-09 13:30 +0200
  RE: [PATCH 0/6] staging: comedi: fix some minor issues with file poll  op Hartley Sweeten <HartleyS@visionengravers.com> - 2015-10-09 19:30 +0200

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