linux-kernel - [PATCH AUTOSEL 4.14 070/105] media: hdpvr: fix locking and a missing msleep

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Date:   Mon, 15 Jul 2019 10:28:04 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Hans Verkuil <hverkuil@...all.nl>,
        Keith Pyle <kpyle@...tin.rr.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Sasha Levin <sashal@...nel.org>, linux-media@...r.kernel.org
Subject: [PATCH AUTOSEL 4.14 070/105] media: hdpvr: fix locking and a missing msleep

From: Hans Verkuil <hverkuil@...all.nl>

[ Upstream commit 6bc5a4a1927556ff9adce1aa95ea408c95453225 ]

This driver has three locking issues:

- The wait_event_interruptible() condition calls hdpvr_get_next_buffer(dev)
  which uses a mutex, which is not allowed. Rewrite with list_empty_careful()
  that doesn't need locking.

- In hdpvr_read() the call to hdpvr_stop_streaming() didn't lock io_mutex,
  but it should have since stop_streaming expects that.

- In hdpvr_device_release() io_mutex was locked when calling flush_work(),
  but there it shouldn't take that mutex since the work done by flush_work()
  also wants to lock that mutex.

There are also two other changes (suggested by Keith):

- msecs_to_jiffies(4000); (a NOP) should have been msleep(4000).
- Change v4l2_dbg to v4l2_info to always log if streaming had to be restarted.

Reported-by: Keith Pyle <kpyle@...tin.rr.com>
Suggested-by: Keith Pyle <kpyle@...tin.rr.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@...all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/media/usb/hdpvr/hdpvr-video.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/media/usb/hdpvr/hdpvr-video.c b/drivers/media/usb/hdpvr/hdpvr-video.c
index 7fb036d6a86e..991f820a4530 100644
--- a/drivers/media/usb/hdpvr/hdpvr-video.c
+++ b/drivers/media/usb/hdpvr/hdpvr-video.c
@@ -439,7 +439,7 @@ static ssize_t hdpvr_read(struct file *file, char __user *buffer, size_t count,
 	/* wait for the first buffer */
 	if (!(file->f_flags & O_NONBLOCK)) {
 		if (wait_event_interruptible(dev->wait_data,
-					     hdpvr_get_next_buffer(dev)))
+					     !list_empty_careful(&dev->rec_buff_list)))
 			return -ERESTARTSYS;
 	}
 
@@ -465,10 +465,17 @@ static ssize_t hdpvr_read(struct file *file, char __user *buffer, size_t count,
 				goto err;
 			}
 			if (!err) {
-				v4l2_dbg(MSG_INFO, hdpvr_debug, &dev->v4l2_dev,
-					"timeout: restart streaming\n");
+				v4l2_info(&dev->v4l2_dev,
+					  "timeout: restart streaming\n");
+				mutex_lock(&dev->io_mutex);
 				hdpvr_stop_streaming(dev);
-				msecs_to_jiffies(4000);
+				mutex_unlock(&dev->io_mutex);
+				/*
+				 * The FW needs about 4 seconds after streaming
+				 * stopped before it is ready to restart
+				 * streaming.
+				 */
+				msleep(4000);
 				err = hdpvr_start_streaming(dev);
 				if (err) {
 					ret = err;
@@ -1133,9 +1140,7 @@ static void hdpvr_device_release(struct video_device *vdev)
 	struct hdpvr_device *dev = video_get_drvdata(vdev);
 
 	hdpvr_delete(dev);
-	mutex_lock(&dev->io_mutex);
 	flush_work(&dev->worker);
-	mutex_unlock(&dev->io_mutex);
 
 	v4l2_device_unregister(&dev->v4l2_dev);
 	v4l2_ctrl_handler_free(&dev->hdl);
-- 
2.20.1