[PATCH 5/6] media: dvb-core: dmxdev: wake up readers on release

[Josef Schlehofer <pepe.schlehofer@gmail.com>]

dvb_dmxdev_release() sets dmxdev->exit and waits for open demux and DVR
files to close, but readers blocked in dvb_dmxdev_buffer_read() wait
only for data or buffer->error. Setting exit therefore does not wake a
blocked read or epoll wait. The release, for example on a USB
disconnect, then waits forever.

Set -ENODEV on the DVR buffer and open filter buffers, wake their wait
queues, and return -ENODEV from dvb_demux_read() once exit is set. Do
not flush buffers when consuming -ENODEV so all readers see the error.

Blocking DMX_DQBUF waiters are not covered.

Fixes: 57861b432bda ("V4L/DVB (5511): Fix 2/3 for bug 7819: demux and dvr")
Cc: stable@vger.kernel.org
Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
---
 drivers/media/dvb-core/dmxdev.c | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/drivers/media/dvb-core/dmxdev.c b/drivers/media/dvb-core/dmxdev.c
index 6a825d9bae43..5f872bc89345 100644
--- a/drivers/media/dvb-core/dmxdev.c
+++ b/drivers/media/dvb-core/dmxdev.c
@@ -63,7 +63,9 @@ static ssize_t dvb_dmxdev_buffer_read(struct dvb_ringbuffer *src,
 
 	if (src->error) {
 		ret = src->error;
-		dvb_ringbuffer_flush(src);
+		/* -ENODEV: the demux is gone for good, keep it for all readers */
+		if (ret != -ENODEV)
+			dvb_ringbuffer_flush(src);
 		return ret;
 	}
 
@@ -81,7 +83,8 @@ static ssize_t dvb_dmxdev_buffer_read(struct dvb_ringbuffer *src,
 
 		if (src->error) {
 			ret = src->error;
-			dvb_ringbuffer_flush(src);
+			if (ret != -ENODEV)
+				dvb_ringbuffer_flush(src);
 			break;
 		}
 
@@ -1035,6 +1038,9 @@ dvb_demux_read(struct file *file, char __user *buf, size_t count,
 	struct dmxdev_filter *dmxdevfilter = file->private_data;
 	int ret;
 
+	if (dmxdevfilter->dev->exit)
+		return -ENODEV;
+
 	if (mutex_lock_interruptible(&dmxdevfilter->mutex))
 		return -ERESTARTSYS;
 
@@ -1457,8 +1463,29 @@ EXPORT_SYMBOL(dvb_dmxdev_init);
 
 void dvb_dmxdev_release(struct dmxdev *dmxdev)
 {
+	int i;
+
 	mutex_lock(&dmxdev->mutex);
 	dmxdev->exit = 1;
+
+	/*
+	 * Wake up everyone blocked in read() or poll() on the demux and dvr
+	 * devices, so that they see the error, close their file handles and
+	 * let the waits below finish.
+	 */
+	spin_lock_irq(&dmxdev->lock);
+	dmxdev->dvr_buffer.error = -ENODEV;
+	for (i = 0; i < dmxdev->filternum; i++) {
+		if (dmxdev->filter[i].state >= DMXDEV_STATE_ALLOCATED)
+			dmxdev->filter[i].buffer.error = -ENODEV;
+	}
+	spin_unlock_irq(&dmxdev->lock);
+
+	wake_up_all(&dmxdev->dvr_buffer.queue);
+	for (i = 0; i < dmxdev->filternum; i++) {
+		if (dmxdev->filter[i].state >= DMXDEV_STATE_ALLOCATED)
+			wake_up_all(&dmxdev->filter[i].buffer.queue);
+	}
 	mutex_unlock(&dmxdev->mutex);
 
 	if (dmxdev->dvbdev->users > 1) {
-- 
2.54.0 (Apple Git-157)