Hi Daniel, Thank you for the patch. On Sunday, 23 April 2017 07:53:49 EET Daniel Axtens wrote: > Currently, disconnecting a USB webcam while it is in use prints out a > number of warnings, such as: > > WARNING: CPU: 2 PID: 3118 at > /build/linux-ezBi1T/linux-4.8.0/fs/sysfs/group.c:237 > sysfs_remove_group+0x8b/0x90 sysfs group ffffffffa7cd0780 not found for > kobject 'event13' > > This has been noticed before. [0] > > This is because of the order in which things are torn down. > > If there are no streams active during a USB disconnect: > > - uvc_disconnect() is invoked via device_del() through the bus > notifier mechanism. > > - this calls uvc_unregister_video(). > > - uvc_unregister_video() unregisters the video device for each > stream, > > - because there are no streams open, it calls uvc_delete() > > - uvc_delete() calls uvc_status_cleanup(), which cleans up the status > input device. > > - uvc_delete() calls media_device_unregister(), which cleans up the > media device > > - uvc_delete(), uvc_unregister_video() and uvc_disconnect() all > return, and we end up back in device_del(). > > - device_del() then cleans up the sysfs folder for the camera with > dpm_sysfs_remove(). Because uvc_status_cleanup() and > media_device_unregister() have already been called, this all works > nicely. > > If, on the other hand, there *are* streams active during a USB disconnect: > > - uvc_disconnect() is invoked > > - this calls uvc_unregister_video() > > - uvc_unregister_video() unregisters the video device for each > stream, > > - uvc_unregister_video() and uvc_disconnect() return, and we end up > back in device_del(). > > - device_del() then cleans up the sysfs folder for the camera with > dpm_sysfs_remove(). Because the status input device and the media > device are children of the USB device, this also deletes their > sysfs folders. > > - Sometime later, the final stream is closed, invoking uvc_release(). > > - uvc_release() calls uvc_delete() > > - uvc_delete() calls uvc_status_cleanup(), which cleans up the status > input device. Because the sysfs directory has already been removed, > this causes a WARNing. > > - uvc_delete() calls media_device_unregister(), which cleans up the > media device. Because the sysfs directory has already been removed, > this causes another WARNing. > > To fix this, we need to make sure the devices are always unregistered > before the end of uvc_disconnect(). To this, move the unregistration > into the disconnect path: > > - split uvc_status_cleanup() into two parts, one on disconnect that > unregisters and one on delete that frees. > > - move v4l2_device_unregister() and media_device_unregister() into > the disconnect path. > > [0]: https://lkml.org/lkml/2016/12/8/657 > > Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > Cc: Dave Stevenson <linux-media@xxxxxxxxxxxxxxxxxxxxxxxxxxx> > Cc: Greg KH <greg@xxxxxxxxx> > Signed-off-by: Daniel Axtens <dja@xxxxxxxxxx> > > --- > > v2: Move v4l2_device_unregister() as well as media_device_unregister(), > thanks Laurent. > > Tested with cheese and yavta. > > Laurent, I know you were concerned about race conditions so I plugged > and unplugged the camera over a dozen times, with lots of debugging > turned on. > > In particular: > - KASan was enabled and didn't trigger > - If I unplugged while yavta was running, and replugged *while yatva > was still running*, the video camera came up as video2, not video1. > This indicates that yatva was successfully holding a reference to > video1 - as it should. > - No other debugging triggered any warning. Thank you for running those tests. I'm still a bit concerned but I'll live with it. The issues are in the MC and V4L2 core anyway, there isn't much we could do here to fix them. > --- > drivers/media/usb/uvc/uvc_driver.c | 12 ++++++++---- > drivers/media/usb/uvc/uvc_status.c | 8 ++++++-- > drivers/media/usb/uvc/uvcvideo.h | 1 + > 3 files changed, 15 insertions(+), 6 deletions(-) > > diff --git a/drivers/media/usb/uvc/uvc_driver.c > b/drivers/media/usb/uvc/uvc_driver.c index 46d6be0bb316..0d0541054ce2 > 100644 > --- a/drivers/media/usb/uvc/uvc_driver.c > +++ b/drivers/media/usb/uvc/uvc_driver.c > @@ -1812,11 +1812,7 @@ static void uvc_delete(struct uvc_device *dev) > usb_put_intf(dev->intf); > usb_put_dev(dev->udev); > > - if (dev->vdev.dev) > - v4l2_device_unregister(&dev->vdev); > #ifdef CONFIG_MEDIA_CONTROLLER > - if (media_devnode_is_registered(dev->mdev.devnode)) > - media_device_unregister(&dev->mdev); > media_device_cleanup(&dev->mdev); > #endif > > @@ -1884,6 +1880,14 @@ static void uvc_unregister_video(struct uvc_device > *dev) uvc_debugfs_cleanup_stream(stream); > } > > + uvc_status_unregister(dev); > + if (dev->vdev.dev) > + v4l2_device_unregister(&dev->vdev); > +#ifdef CONFIG_MEDIA_CONTROLLER > + if (media_devnode_is_registered(dev->mdev.devnode)) > + media_device_unregister(&dev->mdev); > +#endif > + > /* Decrement the stream count and call uvc_delete explicitly if there > * are no stream left. > */ > diff --git a/drivers/media/usb/uvc/uvc_status.c > b/drivers/media/usb/uvc/uvc_status.c index f552ab997956..95709b23d3b4 > 100644 > --- a/drivers/media/usb/uvc/uvc_status.c > +++ b/drivers/media/usb/uvc/uvc_status.c > @@ -198,12 +198,16 @@ int uvc_status_init(struct uvc_device *dev) > return 0; > } > > -void uvc_status_cleanup(struct uvc_device *dev) > +void uvc_status_unregister(struct uvc_device *dev) > { > usb_kill_urb(dev->int_urb); > + uvc_input_cleanup(dev); I think it would make sense to rename uvc_input_cleanup() to uvc_input_unregister(). I'll make the change locally so there's no need to resubmit this patch. Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> and applied to my tree. > +} > + > +void uvc_status_cleanup(struct uvc_device *dev) > +{ > usb_free_urb(dev->int_urb); > kfree(dev->status); > - uvc_input_cleanup(dev); > } > > int uvc_status_start(struct uvc_device *dev, gfp_t flags) [snip] -- Regards, Laurent Pinchart
