linux-kernel - [PATCH] media: uvcvideo: Stop stream during unregister

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Message-Id: <20240926-uvc_stop_streaming-v1-1-038180fafe5f@chromium.org>
Date: Thu, 26 Sep 2024 05:59:06 +0000
From: Ricardo Ribalda <ribalda@...omium.org>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
 Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Hans Verkuil <hverkuil-cisco@...all.nl>, 
 Ricardo Ribalda <ribalda@...omium.org>
Subject: [PATCH] media: uvcvideo: Stop stream during unregister

uvc_unregister_video() can be called asynchronously from
uvc_disconnect(). If the device is still streaming when that happens, a
plethora of race conditions can occur.

Make sure that the device has stopped streaming before exiting this
function.

If the user still holds handles to the driver's file descriptors, any
ioctl will return -ENODEV from the v4l2 core.

This change makes uvc more consistent with the rest of the v4l2 drivers
using the vb2_fop_* and vb2_ioctl_* helpers.

Reviewed-by: Hans Verkuil <hverkuil-cisco@...all.nl>
Suggested-by: Hans Verkuil <hverkuil-cisco@...all.nl>
Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
---
This patch was part of the series:
https://patchwork.linuxtv.org/project/linux-media/list/?series=13064

Moved out from it to ease the review.
---
 drivers/media/usb/uvc/uvc_driver.c | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index f0febdc08c2d..bee150b852e4 100644
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -1919,11 +1919,41 @@ static void uvc_unregister_video(struct uvc_device *dev)
 	struct uvc_streaming *stream;
 
 	list_for_each_entry(stream, &dev->streams, list) {
+		/* Nothing to do here, continue. */
 		if (!video_is_registered(&stream->vdev))
 			continue;
 
+		/*
+		 * For stream->vdev we follow the same logic as:
+		 * vb2_video_unregister_device().
+		 */
+
+		/* 1. Take a reference to vdev */
+		get_device(&stream->vdev.dev);
+
+		/* 2. Ensure that no new ioctls can be called. */
 		video_unregister_device(&stream->vdev);
-		video_unregister_device(&stream->meta.vdev);
+
+		/* 3. Wait for old ioctls to finish. */
+		mutex_lock(&stream->mutex);
+
+		/* 4. Stop streaming. */
+		uvc_queue_release(&stream->queue);
+
+		mutex_unlock(&stream->mutex);
+
+		put_device(&stream->vdev.dev);
+
+		/*
+		 * For stream->meta.vdev we can directly call:
+		 * vb2_video_unregister_device().
+		 */
+		vb2_video_unregister_device(&stream->meta.vdev);
+
+		/*
+		 * Now both vdevs are not streaming and all the ioctls will
+		 * return -ENODEV.
+		 */
 
 		uvc_debugfs_cleanup_stream(stream);
 	}

---
base-commit: 81ee62e8d09ee3c7107d11c8bbfd64073ab601ad
change-id: 20240926-uvc_stop_streaming-6e9fd20e97bc

Best regards,
-- 
Ricardo Ribalda <ribalda@...omium.org>