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 <20231122-guenter-mini-v5-3-15d8cd8ed74f@chromium.org> <20231122133330.GE3909@pendragon.ideasonboard.com>
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From:   Ricardo Ribalda <ribalda@chromium.org>
Date:   Wed, 22 Nov 2023 15:59:10 +0100
Message-ID: <CANiDSCunxALoBJg-u_s=A1Zi-NF3SaNRFhv3=2jTx0oeAPrCZw@mail.gmail.com>
Subject: Re: [PATCH v5 3/3] media: uvcvideo: Do not use usb_* functions after .disconnect
To:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc:     Mauro Carvalho Chehab <mchehab@kernel.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Tomasz Figa <tfiga@chromium.org>,
        Alan Stern <stern@rowland.harvard.edu>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        Sean Paul <seanpaul@chromium.org>,
        Sakari Ailus <sakari.ailus@linux.intel.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Hi Laurent

On Wed, 22 Nov 2023 at 14:33, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> On Wed, Nov 22, 2023 at 11:45:49AM +0000, Ricardo Ribalda wrote:
> > usb drivers should not call to any I/O function after the
> > .disconnect() callback has been triggered.
> > https://www.kernel.org/doc/html/latest/driver-api/usb/callbacks.html#the-disconnect-callback
> >
> > If an application is receiving frames form a camera and the device is
> > disconnected: the device will call close() after the usb .disconnect()
> > callback has been called. The streamoff path will call usb_set_interface
> > or usb_clear_halt, which is not allowed.
> >
> > This patch only solves the calls to close() *after* .disconnect() is
> > being called.
> >
> > Trace:
> > [ 1065.389723] drivers/media/usb/uvc/uvc_driver.c:2248 uvc_disconnect enter
> > [ 1065.390160] drivers/media/usb/uvc/uvc_driver.c:2264 uvc_disconnect exit
> > [ 1065.433956] drivers/media/usb/uvc/uvc_v4l2.c:659 uvc_v4l2_release enter
> > [ 1065.433973] drivers/media/usb/uvc/uvc_video.c:2274 uvc_video_stop_streaming enter
> > [ 1065.434560] drivers/media/usb/uvc/uvc_video.c:2285 uvc_video_stop_streaming exit
> > [ 1065.435154] drivers/media/usb/uvc/uvc_v4l2.c:680 uvc_v4l2_release exit
> > [ 1065.435188] drivers/media/usb/uvc/uvc_driver.c:2248 uvc_disconnect enter
> >
> > Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> > ---
> >  drivers/media/usb/uvc/uvc_driver.c |  2 ++
> >  drivers/media/usb/uvc/uvc_video.c  | 45 ++++++++++++++++++++++++--------------
> >  drivers/media/usb/uvc/uvcvideo.h   |  2 ++
> >  3 files changed, 32 insertions(+), 17 deletions(-)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> > index d5dbf2644272..d78640d422f4 100644
> > --- a/drivers/media/usb/uvc/uvc_driver.c
> > +++ b/drivers/media/usb/uvc/uvc_driver.c
> > @@ -2266,6 +2266,8 @@ static void uvc_disconnect(struct usb_interface *intf)
> >               return;
> >
> >       uvc_unregister_video(dev);
> > +     /* Barrier needed to pair with uvc_video_stop_streaming(). */
> > +     smp_store_release(&dev->disconnected, true);
>
> I can't think this would be such a hot path that we really need barriers
> in the driver.

Using the same variable from two contexts without any sync feels weird.

Your concern is that there will be a big penalty by using the
barriers? This is only used in stop_streaming and the shutdown path.

Regards!

>
> >       kref_put(&dev->ref, uvc_delete);
> >  }
> >
> > diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> > index 28dde08ec6c5..f5ef375088de 100644
> > --- a/drivers/media/usb/uvc/uvc_video.c
> > +++ b/drivers/media/usb/uvc/uvc_video.c
> > @@ -2243,28 +2243,39 @@ int uvc_video_start_streaming(struct uvc_streaming *stream)
> >       return ret;
> >  }
> >
> > -void uvc_video_stop_streaming(struct uvc_streaming *stream)
> > +static void uvc_video_halt(struct uvc_streaming *stream)
> >  {
> > -     uvc_video_stop_transfer(stream, 1);
> > +     unsigned int epnum;
> > +     unsigned int pipe;
> > +     unsigned int dir;
> >
> >       if (stream->intf->num_altsetting > 1) {
> >               usb_set_interface(stream->dev->udev, stream->intfnum, 0);
> > -     } else {
> > -             /*
> > -              * UVC doesn't specify how to inform a bulk-based device
> > -              * when the video stream is stopped. Windows sends a
> > -              * CLEAR_FEATURE(HALT) request to the video streaming
> > -              * bulk endpoint, mimic the same behaviour.
> > -              */
> > -             unsigned int epnum = stream->header.bEndpointAddress
> > -                                & USB_ENDPOINT_NUMBER_MASK;
> > -             unsigned int dir = stream->header.bEndpointAddress
> > -                              & USB_ENDPOINT_DIR_MASK;
> > -             unsigned int pipe;
> > -
> > -             pipe = usb_sndbulkpipe(stream->dev->udev, epnum) | dir;
> > -             usb_clear_halt(stream->dev->udev, pipe);
> > +             return;
> >       }
> >
> > +     /*
> > +      * UVC doesn't specify how to inform a bulk-based device
> > +      * when the video stream is stopped. Windows sends a
> > +      * CLEAR_FEATURE(HALT) request to the video streaming
> > +      * bulk endpoint, mimic the same behaviour.
> > +      */
> > +     epnum = stream->header.bEndpointAddress & USB_ENDPOINT_NUMBER_MASK;
> > +     dir = stream->header.bEndpointAddress & USB_ENDPOINT_DIR_MASK;
> > +     pipe = usb_sndbulkpipe(stream->dev->udev, epnum) | dir;
> > +     usb_clear_halt(stream->dev->udev, pipe);
> > +}
> > +
> > +void uvc_video_stop_streaming(struct uvc_streaming *stream)
> > +{
> > +     uvc_video_stop_transfer(stream, 1);
> > +
> > +     /*
> > +      * Barrier needed to pair with uvc_disconnect().
> > +      * We cannot call usb_* functions on a disconnected USB device.
> > +      */
> > +     if (!smp_load_acquire(&stream->dev->disconnected))
> > +             uvc_video_halt(stream);
> > +
> >       uvc_video_clock_cleanup(stream);
> >  }
> > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > index ba8f8c1f2c83..5b1a3643de05 100644
> > --- a/drivers/media/usb/uvc/uvcvideo.h
> > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > @@ -559,6 +559,8 @@ struct uvc_device {
> >       unsigned int users;
> >       atomic_t nmappings;
> >
> > +     bool disconnected;
> > +
> >       /* Video control interface */
> >  #ifdef CONFIG_MEDIA_CONTROLLER
> >       struct media_device mdev;
> >
>
> --
> Regards,
>
> Laurent Pinchart


--
Ricardo Ribalda