linux-kernel - Re: [PATCH v2 1/2] media: uvcvideo: Fix race condition with usb_kill

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Date:   Wed, 14 Dec 2022 13:04:41 +0900
From:   Yunke Cao <yunkec@...omium.org>
To:     Ricardo Ribalda <ribalda@...omium.org>
Cc:     Max Staudt <mstaudt@...gle.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] media: uvcvideo: Fix race condition with usb_kill_urb

On Tue, Dec 13, 2022 at 11:36 PM Ricardo Ribalda <ribalda@...omium.org> wrote:
>
> usb_kill_urb warranties that all the handlers are finished when it
> returns, but does not protect against threads that might be handling
> asynchronously the urb.
>
> For UVC, the function uvc_ctrl_status_event_async() takes care of
> control changes asynchronously.
>
>  If the code is executed in the following order:
>
> CPU 0                                   CPU 1
> =====                                   =====
> uvc_status_complete()
>                                         uvc_status_stop()
> uvc_ctrl_status_event_work()
>                                         uvc_status_start() -> FAIL
>
> Then uvc_status_start will keep failing and this error will be shown:
>
> <4>[    5.540139] URB 0000000000000000 submitted while active
> drivers/usb/core/urb.c:378 usb_submit_urb+0x4c3/0x528
>
> Let's improve the current situation, by not re-submiting the urb if
> we are stopping the status event. Also process the queued work
> (if any) during stop.
>
> CPU 0                                   CPU 1
> =====                                   =====
> uvc_status_complete()
>                                         uvc_status_stop()
>                                         uvc_status_start()
> uvc_ctrl_status_event_work() -> FAIL
>
> Hopefully, with the usb layer protection this should be enough to cover
> all the cases.
>
> Cc: stable@...r.kernel.org
> Fixes: e5225c820c05 ("media: uvcvideo: Send a control event when a Control Change interrupt arrives")
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  drivers/media/usb/uvc/uvc_ctrl.c   | 3 +++
>  drivers/media/usb/uvc/uvc_status.c | 6 ++++++
>  drivers/media/usb/uvc/uvcvideo.h   | 1 +
>  3 files changed, 10 insertions(+)
>
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> index c95a2229f4fa..5160facc8e20 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> @@ -1442,6 +1442,9 @@ static void uvc_ctrl_status_event_work(struct work_struct *work)
>
>         uvc_ctrl_status_event(w->chain, w->ctrl, w->data);
>
> +       if (dev->flush_status)
> +               return;
> +
>         /* Resubmit the URB. */
>         w->urb->interval = dev->int_ep->desc.bInterval;
>         ret = usb_submit_urb(w->urb, GFP_KERNEL);
> diff --git a/drivers/media/usb/uvc/uvc_status.c b/drivers/media/usb/uvc/uvc_status.c
> index 7518ffce22ed..09a5802dc974 100644
> --- a/drivers/media/usb/uvc/uvc_status.c
> +++ b/drivers/media/usb/uvc/uvc_status.c
> @@ -304,10 +304,16 @@ int uvc_status_start(struct uvc_device *dev, gfp_t flags)
>         if (dev->int_urb == NULL)
>                 return 0;
>
> +       dev->flush_status = false;
>         return usb_submit_urb(dev->int_urb, flags);
>  }
>
>  void uvc_status_stop(struct uvc_device *dev)
>  {
> +       struct uvc_ctrl_work *w = &dev->async_ctrl;
> +
> +       dev->flush_status = true;
>         usb_kill_urb(dev->int_urb);
> +       if (cancel_work_sync(&w->work))
> +               uvc_ctrl_status_event(w->chain, w->ctrl, w->data);
>  }
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> index df93db259312..6a9b72d6789e 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -560,6 +560,7 @@ struct uvc_device {
>         struct usb_host_endpoint *int_ep;
>         struct urb *int_urb;
>         u8 *status;
> +       bool flush_status;
>         struct input_dev *input;
>         char input_phys[64];
>
>
> --
> 2.39.0.rc1.256.g54fd8350bd-goog-b4-0.11.0-dev-696ae

Reviewed-by: Yunke Cao <yunkec@...omium.org>