media: dvb-core: fix epoll() by calling poll_wait first

The epoll function expects that whenever the poll file op is
called, the poll_wait function is also called. That didn't
always happen in dvb_demux_poll(), dvb_dvr_poll() and
dvb_ca_en50221_io_poll(). Fix this, otherwise epoll()
can timeout when it shouldn't.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/dvb-core/dmxdev.c

@@ -1195,13 +1195,13 @@ static __poll_t dvb_demux_poll(struct file *file, poll_table *wait)
 	struct dmxdev_filter *dmxdevfilter = file->private_data;
 	__poll_t mask = 0;
 
+	poll_wait(file, &dmxdevfilter->buffer.queue, wait);
+
 	if ((!dmxdevfilter) || dmxdevfilter->dev->exit)
 		return EPOLLERR;
 	if (dvb_vb2_is_streaming(&dmxdevfilter->vb2_ctx))
 		return dvb_vb2_poll(&dmxdevfilter->vb2_ctx, file, wait);
 
-	poll_wait(file, &dmxdevfilter->buffer.queue, wait);
-
 	if (dmxdevfilter->state != DMXDEV_STATE_GO &&
 	    dmxdevfilter->state != DMXDEV_STATE_DONE &&
 	    dmxdevfilter->state != DMXDEV_STATE_TIMEDOUT)
@@ -1346,13 +1346,13 @@ static __poll_t dvb_dvr_poll(struct file *file, poll_table *wait)
 
 	dprintk("%s\n", __func__);
 
+	poll_wait(file, &dmxdev->dvr_buffer.queue, wait);
+
 	if (dmxdev->exit)
 		return EPOLLERR;
 	if (dvb_vb2_is_streaming(&dmxdev->dvr_vb2_ctx))
 		return dvb_vb2_poll(&dmxdev->dvr_vb2_ctx, file, wait);
 
-	poll_wait(file, &dmxdev->dvr_buffer.queue, wait);
-
 	if (((file->f_flags & O_ACCMODE) == O_RDONLY) ||
 	    dmxdev->may_do_mmap) {
 		if (dmxdev->dvr_buffer.error)

drivers/media/dvb-core/dvb_ca_en50221.c

@@ -1797,6 +1797,8 @@ static __poll_t dvb_ca_en50221_io_poll(struct file *file, poll_table *wait)
 
 	dprintk("%s\n", __func__);
 
+	poll_wait(file, &ca->wait_queue, wait);
+
 	if (dvb_ca_en50221_io_read_condition(ca, &result, &slot) == 1)
 		mask |= EPOLLIN;
 
@@ -1804,9 +1806,6 @@ static __poll_t dvb_ca_en50221_io_poll(struct file *file, poll_table *wait)
 	if (mask)
 		return mask;
 
-	/* wait for something to happen */
-	poll_wait(file, &ca->wait_queue, wait);
-
 	if (dvb_ca_en50221_io_read_condition(ca, &result, &slot) == 1)
 		mask |= EPOLLIN;