| Message ID | 20241105-uvc-rmrefcount-v1-1-123f56b01731@chromium.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | media: uvcvideo: Remove refcounted cleanup | expand |
On Tue, Nov 05, 2024 at 02:32:39PM +0000, Ricardo Ribalda wrote: > After commit c9ec6f173636 ("media: uvcvideo: Stop stream during unregister") > we have some guarantee that userspace will not be able to access any of > our internal structures after disconnect(). > > This means that we can do the cleanup at the end of disconnect and make > the code more resilient to races. > > This change will also enable the use of devres functions in more parts > of the code. That's the wrong direction, let's not go there, especially given that this doesn't fix anything. Strong nack on my side, especially given how many of your previous patches introduced race conditions. It's not broken, don't touch it. A better use of your time would be to fix the unplug race issue at the subsystem level. > Signed-off-by: Ricardo Ribalda <ribalda@chromium.org> > --- > drivers/media/usb/uvc/uvc_driver.c | 24 +++++------------------- > drivers/media/usb/uvc/uvcvideo.h | 1 - > 2 files changed, 5 insertions(+), 20 deletions(-) > > diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c > index a96f6ca0889f..2735fccdf454 100644 > --- a/drivers/media/usb/uvc/uvc_driver.c > +++ b/drivers/media/usb/uvc/uvc_driver.c > @@ -1868,16 +1868,12 @@ static int uvc_scan_device(struct uvc_device *dev) > /* > * Delete the UVC device. > * > - * Called by the kernel when the last reference to the uvc_device structure > - * is released. > - * > - * As this function is called after or during disconnect(), all URBs have > + * As this function is called during disconnect(), all URBs have > * already been cancelled by the USB core. There is no need to kill the > * interrupt URB manually. > */ > -static void uvc_delete(struct kref *kref) > +static void uvc_delete(struct uvc_device *dev) > { > - struct uvc_device *dev = container_of(kref, struct uvc_device, ref); > struct list_head *p, *n; > > uvc_status_cleanup(dev); > @@ -1919,14 +1915,6 @@ static void uvc_delete(struct kref *kref) > kfree(dev); > } > > -static void uvc_release(struct video_device *vdev) > -{ > - struct uvc_streaming *stream = video_get_drvdata(vdev); > - struct uvc_device *dev = stream->dev; > - > - kref_put(&dev->ref, uvc_delete); > -} > - > /* > * Unregister the video devices. > */ > @@ -2009,7 +1997,7 @@ int uvc_register_video_device(struct uvc_device *dev, > vdev->v4l2_dev = &dev->vdev; > vdev->fops = fops; > vdev->ioctl_ops = ioctl_ops; > - vdev->release = uvc_release; > + vdev->release = video_device_release_empty; > vdev->prio = &stream->chain->prio; > if (type == V4L2_BUF_TYPE_VIDEO_OUTPUT) > vdev->vfl_dir = VFL_DIR_TX; > @@ -2045,7 +2033,6 @@ int uvc_register_video_device(struct uvc_device *dev, > return ret; > } > > - kref_get(&dev->ref); > return 0; > } > > @@ -2160,7 +2147,6 @@ static int uvc_probe(struct usb_interface *intf, > INIT_LIST_HEAD(&dev->entities); > INIT_LIST_HEAD(&dev->chains); > INIT_LIST_HEAD(&dev->streams); > - kref_init(&dev->ref); > atomic_set(&dev->nmappings, 0); > > dev->udev = usb_get_dev(udev); > @@ -2300,7 +2286,7 @@ static int uvc_probe(struct usb_interface *intf, > > error: > uvc_unregister_video(dev); > - kref_put(&dev->ref, uvc_delete); > + uvc_delete(dev); > return -ENODEV; > } > > @@ -2319,7 +2305,7 @@ static void uvc_disconnect(struct usb_interface *intf) > return; > > uvc_unregister_video(dev); > - kref_put(&dev->ref, uvc_delete); > + uvc_delete(dev); > } > > static int uvc_suspend(struct usb_interface *intf, pm_message_t message) > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h > index 07f9921d83f2..feb8de640a26 100644 > --- a/drivers/media/usb/uvc/uvcvideo.h > +++ b/drivers/media/usb/uvc/uvcvideo.h > @@ -578,7 +578,6 @@ struct uvc_device { > > /* Video Streaming interfaces */ > struct list_head streams; > - struct kref ref; > > /* Status Interrupt Endpoint */ > struct usb_host_endpoint *int_ep; > > --- > base-commit: c7ccf3683ac9746b263b0502255f5ce47f64fe0a > change-id: 20241105-uvc-rmrefcount-010d98d496c5
Hi On Tue, 5 Nov 2024 at 15:43, Laurent Pinchart <laurent.pinchart@ideasonboard.com> wrote: > > On Tue, Nov 05, 2024 at 02:32:39PM +0000, Ricardo Ribalda wrote: > > After commit c9ec6f173636 ("media: uvcvideo: Stop stream during unregister") > > we have some guarantee that userspace will not be able to access any of > > our internal structures after disconnect(). > > > > This means that we can do the cleanup at the end of disconnect and make > > the code more resilient to races. > > > > This change will also enable the use of devres functions in more parts > > of the code. > > That's the wrong direction, let's not go there, especially given that > this doesn't fix anything. Strong nack on my side, especially given how > many of your previous patches introduced race conditions. It's not They have also fixed some race conditions... keep the discussion professional please. I think this only proves that uvc code is quite complicated. It also lacks a lot of consistency with the rest of the drivers in media (and in the kernel in general) that is exactly what this patch tries to fix. > broken, don't touch it. A better use of your time would be to fix the > unplug race issue at the subsystem level. Now memory is allocated during uvc_probe(), but it is not freed until after disconnect() if userspace has a videodevice open. Luckily userspace now cannot interfere with the driver after disconnect(), so lets make use of that property to simplify the code. As the commit message says, with this change we can start using devm_ functions and we will have less chances to make mistakes Eg: no more - this cleanout belongs to uvc_register_video_device vs uvc_delete - devm_ function fails because it is called too late This patch fixes a class of bugs. I would really appreciate it if you can review it. I have moved it to its own patchset: https://patchwork.linuxtv.org/project/linux-media/patch/20241105-uvc-rmrefcount-v1-1-123f56b01731@chromium.org/ I am planning to send more patches on top of it making use of devres Regards! > > > Signed-off-by: Ricardo Ribalda <ribalda@chromium.org> > > --- > > drivers/media/usb/uvc/uvc_driver.c | 24 +++++------------------- > > drivers/media/usb/uvc/uvcvideo.h | 1 - > > 2 files changed, 5 insertions(+), 20 deletions(-) > > > > diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c > > index a96f6ca0889f..2735fccdf454 100644 > > --- a/drivers/media/usb/uvc/uvc_driver.c > > +++ b/drivers/media/usb/uvc/uvc_driver.c > > @@ -1868,16 +1868,12 @@ static int uvc_scan_device(struct uvc_device *dev) > > /* > > * Delete the UVC device. > > * > > - * Called by the kernel when the last reference to the uvc_device structure > > - * is released. > > - * > > - * As this function is called after or during disconnect(), all URBs have > > + * As this function is called during disconnect(), all URBs have > > * already been cancelled by the USB core. There is no need to kill the > > * interrupt URB manually. > > */ > > -static void uvc_delete(struct kref *kref) > > +static void uvc_delete(struct uvc_device *dev) > > { > > - struct uvc_device *dev = container_of(kref, struct uvc_device, ref); > > struct list_head *p, *n; > > > > uvc_status_cleanup(dev); > > @@ -1919,14 +1915,6 @@ static void uvc_delete(struct kref *kref) > > kfree(dev); > > } > > > > -static void uvc_release(struct video_device *vdev) > > -{ > > - struct uvc_streaming *stream = video_get_drvdata(vdev); > > - struct uvc_device *dev = stream->dev; > > - > > - kref_put(&dev->ref, uvc_delete); > > -} > > - > > /* > > * Unregister the video devices. > > */ > > @@ -2009,7 +1997,7 @@ int uvc_register_video_device(struct uvc_device *dev, > > vdev->v4l2_dev = &dev->vdev; > > vdev->fops = fops; > > vdev->ioctl_ops = ioctl_ops; > > - vdev->release = uvc_release; > > + vdev->release = video_device_release_empty; > > vdev->prio = &stream->chain->prio; > > if (type == V4L2_BUF_TYPE_VIDEO_OUTPUT) > > vdev->vfl_dir = VFL_DIR_TX; > > @@ -2045,7 +2033,6 @@ int uvc_register_video_device(struct uvc_device *dev, > > return ret; > > } > > > > - kref_get(&dev->ref); > > return 0; > > } > > > > @@ -2160,7 +2147,6 @@ static int uvc_probe(struct usb_interface *intf, > > INIT_LIST_HEAD(&dev->entities); > > INIT_LIST_HEAD(&dev->chains); > > INIT_LIST_HEAD(&dev->streams); > > - kref_init(&dev->ref); > > atomic_set(&dev->nmappings, 0); > > > > dev->udev = usb_get_dev(udev); > > @@ -2300,7 +2286,7 @@ static int uvc_probe(struct usb_interface *intf, > > > > error: > > uvc_unregister_video(dev); > > - kref_put(&dev->ref, uvc_delete); > > + uvc_delete(dev); > > return -ENODEV; > > } > > > > @@ -2319,7 +2305,7 @@ static void uvc_disconnect(struct usb_interface *intf) > > return; > > > > uvc_unregister_video(dev); > > - kref_put(&dev->ref, uvc_delete); > > + uvc_delete(dev); > > } > > > > static int uvc_suspend(struct usb_interface *intf, pm_message_t message) > > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h > > index 07f9921d83f2..feb8de640a26 100644 > > --- a/drivers/media/usb/uvc/uvcvideo.h > > +++ b/drivers/media/usb/uvc/uvcvideo.h > > @@ -578,7 +578,6 @@ struct uvc_device { > > > > /* Video Streaming interfaces */ > > struct list_head streams; > > - struct kref ref; > > > > /* Status Interrupt Endpoint */ > > struct usb_host_endpoint *int_ep; > > > > --- > > base-commit: c7ccf3683ac9746b263b0502255f5ce47f64fe0a > > change-id: 20241105-uvc-rmrefcount-010d98d496c5 > > -- > Regards, > > Laurent Pinchart
On Tue, Nov 05, 2024 at 04:36:38PM +0100, Ricardo Ribalda wrote: > On Tue, 5 Nov 2024 at 15:43, Laurent Pinchart wrote: > > On Tue, Nov 05, 2024 at 02:32:39PM +0000, Ricardo Ribalda wrote: > > > After commit c9ec6f173636 ("media: uvcvideo: Stop stream during unregister") > > > we have some guarantee that userspace will not be able to access any of > > > our internal structures after disconnect(). > > > > > > This means that we can do the cleanup at the end of disconnect and make > > > the code more resilient to races. > > > > > > This change will also enable the use of devres functions in more parts > > > of the code. > > > > That's the wrong direction, let's not go there, especially given that > > this doesn't fix anything. Strong nack on my side, especially given how > > many of your previous patches introduced race conditions. It's not > > They have also fixed some race conditions... keep the discussion > professional please. > > I think this only proves that uvc code is quite complicated. It also > lacks a lot of consistency with the rest of the drivers in media (and > in the kernel in general) > that is exactly what this patch tries to fix. > > > broken, don't touch it. A better use of your time would be to fix the > > unplug race issue at the subsystem level. > > Now memory is allocated during uvc_probe(), but it is not freed until > after disconnect() if userspace has a videodevice open. > Luckily userspace now cannot interfere with the driver after > disconnect(), so lets make use of that property to simplify the code. > > As the commit message says, with this change we can start using devm_ > functions and we will have less chances to make mistakes > Eg: no more > - this cleanout belongs to uvc_register_video_device vs uvc_delete > - devm_ function fails because it is called too late > > This patch fixes a class of bugs. I would really appreciate it if you > can review it. > I have moved it to its own patchset: > https://patchwork.linuxtv.org/project/linux-media/patch/20241105-uvc-rmrefcount-v1-1-123f56b01731@chromium.org/ > I am planning to send more patches on top of it making use of devres I currently lack confidence in your patches when it comes to race conditions and use-after-free. For the ones that fix bugs, or introduce new features, I bite the bullet and review them. The most recent example (https://lore.kernel.org/r/20241105-uvc-crashrmmod-v5-1-8623fa51a74f@chromium.org) is a good example of why I lack that confidence. I will prioritize my time to get important uvcvideo patches in as quickly as possible, not on reviewing patches that do not address any issue and have a high risk of introducing problems. If you would like to get this kind of rework in, I recommend rebuilding bridges first and creating trust. I would request you to drop this patch in the meantime. > > > Signed-off-by: Ricardo Ribalda <ribalda@chromium.org> > > > --- > > > drivers/media/usb/uvc/uvc_driver.c | 24 +++++------------------- > > > drivers/media/usb/uvc/uvcvideo.h | 1 - > > > 2 files changed, 5 insertions(+), 20 deletions(-) > > > > > > diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c > > > index a96f6ca0889f..2735fccdf454 100644 > > > --- a/drivers/media/usb/uvc/uvc_driver.c > > > +++ b/drivers/media/usb/uvc/uvc_driver.c > > > @@ -1868,16 +1868,12 @@ static int uvc_scan_device(struct uvc_device *dev) > > > /* > > > * Delete the UVC device. > > > * > > > - * Called by the kernel when the last reference to the uvc_device structure > > > - * is released. > > > - * > > > - * As this function is called after or during disconnect(), all URBs have > > > + * As this function is called during disconnect(), all URBs have > > > * already been cancelled by the USB core. There is no need to kill the > > > * interrupt URB manually. > > > */ > > > -static void uvc_delete(struct kref *kref) > > > +static void uvc_delete(struct uvc_device *dev) > > > { > > > - struct uvc_device *dev = container_of(kref, struct uvc_device, ref); > > > struct list_head *p, *n; > > > > > > uvc_status_cleanup(dev); > > > @@ -1919,14 +1915,6 @@ static void uvc_delete(struct kref *kref) > > > kfree(dev); > > > } > > > > > > -static void uvc_release(struct video_device *vdev) > > > -{ > > > - struct uvc_streaming *stream = video_get_drvdata(vdev); > > > - struct uvc_device *dev = stream->dev; > > > - > > > - kref_put(&dev->ref, uvc_delete); > > > -} > > > - > > > /* > > > * Unregister the video devices. > > > */ > > > @@ -2009,7 +1997,7 @@ int uvc_register_video_device(struct uvc_device *dev, > > > vdev->v4l2_dev = &dev->vdev; > > > vdev->fops = fops; > > > vdev->ioctl_ops = ioctl_ops; > > > - vdev->release = uvc_release; > > > + vdev->release = video_device_release_empty; > > > vdev->prio = &stream->chain->prio; > > > if (type == V4L2_BUF_TYPE_VIDEO_OUTPUT) > > > vdev->vfl_dir = VFL_DIR_TX; > > > @@ -2045,7 +2033,6 @@ int uvc_register_video_device(struct uvc_device *dev, > > > return ret; > > > } > > > > > > - kref_get(&dev->ref); > > > return 0; > > > } > > > > > > @@ -2160,7 +2147,6 @@ static int uvc_probe(struct usb_interface *intf, > > > INIT_LIST_HEAD(&dev->entities); > > > INIT_LIST_HEAD(&dev->chains); > > > INIT_LIST_HEAD(&dev->streams); > > > - kref_init(&dev->ref); > > > atomic_set(&dev->nmappings, 0); > > > > > > dev->udev = usb_get_dev(udev); > > > @@ -2300,7 +2286,7 @@ static int uvc_probe(struct usb_interface *intf, > > > > > > error: > > > uvc_unregister_video(dev); > > > - kref_put(&dev->ref, uvc_delete); > > > + uvc_delete(dev); > > > return -ENODEV; > > > } > > > > > > @@ -2319,7 +2305,7 @@ static void uvc_disconnect(struct usb_interface *intf) > > > return; > > > > > > uvc_unregister_video(dev); > > > - kref_put(&dev->ref, uvc_delete); > > > + uvc_delete(dev); > > > } > > > > > > static int uvc_suspend(struct usb_interface *intf, pm_message_t message) > > > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h > > > index 07f9921d83f2..feb8de640a26 100644 > > > --- a/drivers/media/usb/uvc/uvcvideo.h > > > +++ b/drivers/media/usb/uvc/uvcvideo.h > > > @@ -578,7 +578,6 @@ struct uvc_device { > > > > > > /* Video Streaming interfaces */ > > > struct list_head streams; > > > - struct kref ref; > > > > > > /* Status Interrupt Endpoint */ > > > struct usb_host_endpoint *int_ep; > > > > > > --- > > > base-commit: c7ccf3683ac9746b263b0502255f5ce47f64fe0a > > > change-id: 20241105-uvc-rmrefcount-010d98d496c5
diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c index a96f6ca0889f..2735fccdf454 100644 --- a/drivers/media/usb/uvc/uvc_driver.c +++ b/drivers/media/usb/uvc/uvc_driver.c @@ -1868,16 +1868,12 @@ static int uvc_scan_device(struct uvc_device *dev) /* * Delete the UVC device. * - * Called by the kernel when the last reference to the uvc_device structure - * is released. - * - * As this function is called after or during disconnect(), all URBs have + * As this function is called during disconnect(), all URBs have * already been cancelled by the USB core. There is no need to kill the * interrupt URB manually. */ -static void uvc_delete(struct kref *kref) +static void uvc_delete(struct uvc_device *dev) { - struct uvc_device *dev = container_of(kref, struct uvc_device, ref); struct list_head *p, *n; uvc_status_cleanup(dev); @@ -1919,14 +1915,6 @@ static void uvc_delete(struct kref *kref) kfree(dev); } -static void uvc_release(struct video_device *vdev) -{ - struct uvc_streaming *stream = video_get_drvdata(vdev); - struct uvc_device *dev = stream->dev; - - kref_put(&dev->ref, uvc_delete); -} - /* * Unregister the video devices. */ @@ -2009,7 +1997,7 @@ int uvc_register_video_device(struct uvc_device *dev, vdev->v4l2_dev = &dev->vdev; vdev->fops = fops; vdev->ioctl_ops = ioctl_ops; - vdev->release = uvc_release; + vdev->release = video_device_release_empty; vdev->prio = &stream->chain->prio; if (type == V4L2_BUF_TYPE_VIDEO_OUTPUT) vdev->vfl_dir = VFL_DIR_TX; @@ -2045,7 +2033,6 @@ int uvc_register_video_device(struct uvc_device *dev, return ret; } - kref_get(&dev->ref); return 0; } @@ -2160,7 +2147,6 @@ static int uvc_probe(struct usb_interface *intf, INIT_LIST_HEAD(&dev->entities); INIT_LIST_HEAD(&dev->chains); INIT_LIST_HEAD(&dev->streams); - kref_init(&dev->ref); atomic_set(&dev->nmappings, 0); dev->udev = usb_get_dev(udev); @@ -2300,7 +2286,7 @@ static int uvc_probe(struct usb_interface *intf, error: uvc_unregister_video(dev); - kref_put(&dev->ref, uvc_delete); + uvc_delete(dev); return -ENODEV; } @@ -2319,7 +2305,7 @@ static void uvc_disconnect(struct usb_interface *intf) return; uvc_unregister_video(dev); - kref_put(&dev->ref, uvc_delete); + uvc_delete(dev); } static int uvc_suspend(struct usb_interface *intf, pm_message_t message) diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h index 07f9921d83f2..feb8de640a26 100644 --- a/drivers/media/usb/uvc/uvcvideo.h +++ b/drivers/media/usb/uvc/uvcvideo.h @@ -578,7 +578,6 @@ struct uvc_device { /* Video Streaming interfaces */ struct list_head streams; - struct kref ref; /* Status Interrupt Endpoint */ struct usb_host_endpoint *int_ep;
After commit c9ec6f173636 ("media: uvcvideo: Stop stream during unregister") we have some guarantee that userspace will not be able to access any of our internal structures after disconnect(). This means that we can do the cleanup at the end of disconnect and make the code more resilient to races. This change will also enable the use of devres functions in more parts of the code. Signed-off-by: Ricardo Ribalda <ribalda@chromium.org> --- drivers/media/usb/uvc/uvc_driver.c | 24 +++++------------------- drivers/media/usb/uvc/uvcvideo.h | 1 - 2 files changed, 5 insertions(+), 20 deletions(-) --- base-commit: c7ccf3683ac9746b263b0502255f5ce47f64fe0a change-id: 20241105-uvc-rmrefcount-010d98d496c5 Best regards,