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SubjectRe: [PATCH v3] media: uvcvideo: Fix race condition with usb_kill_urb
Hi Laurent

On Wed, 14 Dec 2022 at 13:41, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> Hi Ricardo,
>
> Thank you for the patch.
>
> On Wed, Dec 14, 2022 at 12:18:52PM +0100, Ricardo Ribalda 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@vger.kernel.org
> > Fixes: e5225c820c05 ("media: uvcvideo: Send a control event when a Control Change interrupt arrives")
> > Reviewed-by: Yunke Cao <yunkec@chromium.org>
> > Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> > ---
> > uvc: Fix race condition on uvc
> >
> > Make sure that all the async work is finished when we stop the status urb.
> >
> > To: Yunke Cao <yunkec@chromium.org>
> > To: Sergey Senozhatsky <senozhatsky@chromium.org>
> > To: Max Staudt <mstaudt@google.com>
> > To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > To: Mauro Carvalho Chehab <mchehab@kernel.org>
> > Cc: linux-media@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
> > ---
> > Changes in v3:
> > - Remove the patch for dev->status, makes more sense in another series, and makes
> > the zero day less nervous.
> > - Update reviewed-by (thanks Yunke!).
> > - Link to v2: https://lore.kernel.org/r/20221212-uvc-race-v2-0-54496cc3b8ab@chromium.org
> >
> > Changes in v2:
> > - Add a patch for not kalloc dev->status
> > - Redo the logic mechanism, so it also works with suspend (Thanks Yunke!)
> > - Link to v1: https://lore.kernel.org/r/20221212-uvc-race-v1-0-c52e1783c31d@chromium.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);
>
> Isn't this still racy ?

Indeed...

I could add a mutex just for flush_status

what do you think?

>
> CPU0 CPU1
> ==== ====
>
> uvc_status_stop() uvc_ctrl_status_event_work()
> { {
> if (dev->flush_status)
> return;
>
> dev->flush_status = true;
> usb_kill_urb(dev->int_urb);
>
> /* Resubmit the URB. */
> w->urb->interval = dev->int_ep->desc.bInterval;
> ret = usb_submit_urb(w->urb, GFP_KERNEL);
> }
>
> if (cancel_work_sync(&w->work))
> uvc_ctrl_status_event(w->chain, w->ctrl, w->data);
> }
>
> uvc_status_start() will then return an error, right ?
>
> > + 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];
> >
> >
> > ---
> > base-commit: 0ec5a38bf8499f403f81cb81a0e3a60887d1993c
> > change-id: 20221212-uvc-race-09276ea68bf8
>
> --
> Regards,
>
> Laurent Pinchart



--
Ricardo Ribalda

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