Re: [PATCH v2 1/3] media: uvcvideo: Cancel async worker earlier

[Tomasz Figa]

On Mon, May 1, 2023 at 10:30 PM Ricardo Ribalda <ribalda@xxxxxxxxxxxx> wrote:
>
> Hi Laurent
>
> Friendly ping!

+Kieran and +Mauro, could you take a look at this please, since
Laurent has not responded to this for almost 2 months?

>
> On Tue, 28 Mar 2023 at 09:52, Ricardo Ribalda <ribalda@xxxxxxxxxxxx> wrote:
> >
> > Hi Laurent
> >
> > I have not tested it yet... but maybe something like this might be
> > slightly better?
> >
> >
> > diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> > index 5e9d3da862dd..3944404b2de2 100644
> > --- a/drivers/media/usb/uvc/uvc_ctrl.c
> > +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> > @@ -2762,10 +2762,6 @@ void uvc_ctrl_cleanup_device(struct uvc_device *dev)
> >         struct uvc_entity *entity;
> >         unsigned int i;
> >
> > -       /* Can be uninitialized if we are aborting on probe error. */
> > -       if (dev->async_ctrl.work.func)
> > -               cancel_work_sync(&dev->async_ctrl.work);
> > -
> >         /* Free controls and control mappings for all entities. */
> >         list_for_each_entry(entity, &dev->entities, list) {
> >                 for (i = 0; i < entity->ncontrols; ++i) {
> > diff --git a/drivers/media/usb/uvc/uvc_status.c
> > b/drivers/media/usb/uvc/uvc_status.c
> > index a78a88c710e2..0208612a9f12 100644
> > --- a/drivers/media/usb/uvc/uvc_status.c
> > +++ b/drivers/media/usb/uvc/uvc_status.c
> > @@ -292,7 +292,7 @@ int uvc_status_init(struct uvc_device *dev)
> >
> >  void uvc_status_unregister(struct uvc_device *dev)
> >  {
> > -       usb_kill_urb(dev->int_urb);
> > +       uvc_status_stop(dev);
> >         uvc_input_unregister(dev);
> >  }
> >
> >
> > The benefit from Guenter patch is that it has been tested for years...
> >
> > What do you think? Shall we try this approach instead?
> >
> > Regards!
> >
> > On Thu, 9 Mar 2023 at 15:57, Laurent Pinchart
> > <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
> > >
> > > Hi Ricardo and Guenter,
> > >
> > > Thank you for the patch.
> > >
> > > On Thu, Mar 09, 2023 at 03:44:05PM +0100, Ricardo Ribalda wrote:
> > > > From: Guenter Roeck <linux@xxxxxxxxxxxx>
> > > >
> > > > So far the asynchronous control worker was canceled only in
> > > > uvc_ctrl_cleanup_device. This is much later than the call to
> > > > uvc_disconnect. However, after the call to uvc_disconnect returns,
> > > > there must be no more USB activity. This can result in all kinds
> > > > of problems in the USB code. One observed example:
> > > >
> > > > URB ffff993e83d0bc00 submitted while active
> > > > WARNING: CPU: 0 PID: 4046 at drivers/usb/core/urb.c:364 usb_submit_urb+0x4ba/0x55e
> > > > Modules linked in: <...>
> > > > CPU: 0 PID: 4046 Comm: kworker/0:35 Not tainted 4.19.139 #18
> > > > Hardware name: Google Phaser/Phaser, BIOS Google_Phaser.10952.0.0 08/09/2018
> > > > Workqueue: events uvc_ctrl_status_event_work [uvcvideo]
> > > > RIP: 0010:usb_submit_urb+0x4ba/0x55e
> > > > Code: <...>
> > > > RSP: 0018:ffffb08d471ebde8 EFLAGS: 00010246
> > > > RAX: a6da85d923ea5d00 RBX: ffff993e71985928 RCX: 0000000000000000
> > > > RDX: ffff993f37a1de90 RSI: ffff993f37a153d0 RDI: ffff993f37a153d0
> > > > RBP: ffffb08d471ebe28 R08: 000000000000003b R09: 001424bf85822e96
> > > > R10: 0000001000000000 R11: ffffffff975a4398 R12: ffff993e83d0b000
> > > > R13: ffff993e83d0bc00 R14: 0000000000000000 R15: 00000000fffffff0
> > > > FS:  0000000000000000(0000) GS:ffff993f37a00000(0000) knlGS:0000000000000000
> > > > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > > CR2: 00000000ec9c0000 CR3: 000000025b160000 CR4: 0000000000340ef0
> > > > Call Trace:
> > > >  uvc_ctrl_status_event_work+0xd6/0x107 [uvcvideo]
> > > >  process_one_work+0x19b/0x4c5
> > > >  worker_thread+0x10d/0x286
> > > >  kthread+0x138/0x140
> > > >  ? process_one_work+0x4c5/0x4c5
> > > >  ? kthread_associate_blkcg+0xc1/0xc1
> > > >  ret_from_fork+0x1f/0x40
> > > >
> > > > Introduce new function uvc_ctrl_stop_device() to cancel the worker
> > > > and call it from uvc_unregister_video() to solve the problem.
> > > >
> > > > Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> > > > Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> > > > Cc: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
> > > > Reviewed-by: Tomasz Figa <tfiga@xxxxxxxxxxxx>
> > > > Reviewed-by: Sean Paul <seanpaul@xxxxxxxxxxxx>
> > > > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > > > Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> > > > ---
> > > >  drivers/media/usb/uvc/uvc_ctrl.c   | 11 +++++++----
> > > >  drivers/media/usb/uvc/uvc_driver.c |  1 +
> > > >  drivers/media/usb/uvc/uvcvideo.h   |  1 +
> > > >  3 files changed, 9 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> > > > index 5e9d3da862dd..769c1d2a2f45 100644
> > > > --- a/drivers/media/usb/uvc/uvc_ctrl.c
> > > > +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> > > > @@ -2757,14 +2757,17 @@ static void uvc_ctrl_cleanup_mappings(struct uvc_device *dev,
> > > >       }
> > > >  }
> > > >
> > > > -void uvc_ctrl_cleanup_device(struct uvc_device *dev)
> > > > +void uvc_ctrl_stop_device(struct uvc_device *dev)
> > > >  {
> > > > -     struct uvc_entity *entity;
> > > > -     unsigned int i;
> > > > -
> > > >       /* Can be uninitialized if we are aborting on probe error. */
> > > >       if (dev->async_ctrl.work.func)
> > > >               cancel_work_sync(&dev->async_ctrl.work);
> > > > +}
> > >
> > > There may be an opportunity for refactoring, as we have
> > > uvc_status_stop() that stops the work queue, but I think this is good
> > > enough for now. I'm wondering, though, if there could be a race
> > > condition here similar to the one that the recent changes to
> > > uvc_status_stop() have fixed ? As uvc_ctrl_stop_device() is called at
> > > release time I assume that URBs have been cancelled, so there should be
> > > no race, but a second pair of eyeballs to confirm this would be
> > > appreciated.
> > >
> > > Other than that, the patch looks good to me, and fixes an issue
> > > independent from the rest of the series, so
> > >
> > > Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> > >
> > > I will wait for a reply regarding the race condition before queuing this
> > > up though.
> > >
> > > > +
> > > > +void uvc_ctrl_cleanup_device(struct uvc_device *dev)
> > > > +{
> > > > +     struct uvc_entity *entity;
> > > > +     unsigned int i;
> > > >
> > > >       /* Free controls and control mappings for all entities. */
> > > >       list_for_each_entry(entity, &dev->entities, list) {
> > > > diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> > > > index 7aefa76a42b3..4be6dfeaa295 100644
> > > > --- a/drivers/media/usb/uvc/uvc_driver.c
> > > > +++ b/drivers/media/usb/uvc/uvc_driver.c
> > > > @@ -1893,6 +1893,7 @@ static void uvc_unregister_video(struct uvc_device *dev)
> > > >       }
> > > >
> > > >       uvc_status_unregister(dev);
> > > > +     uvc_ctrl_stop_device(dev);
> > > >
> > > >       if (dev->vdev.dev)
> > > >               v4l2_device_unregister(&dev->vdev);
> > > > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > > > index 9a596c8d894a..50f171e7381b 100644
> > > > --- a/drivers/media/usb/uvc/uvcvideo.h
> > > > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > > > @@ -760,6 +760,7 @@ int uvc_query_v4l2_menu(struct uvc_video_chain *chain,
> > > >  int uvc_ctrl_add_mapping(struct uvc_video_chain *chain,
> > > >                        const struct uvc_control_mapping *mapping);
> > > >  int uvc_ctrl_init_device(struct uvc_device *dev);
> > > > +void uvc_ctrl_stop_device(struct uvc_device *dev);
> > > >  void uvc_ctrl_cleanup_device(struct uvc_device *dev);
> > > >  int uvc_ctrl_restore_values(struct uvc_device *dev);
> > > >  bool uvc_ctrl_status_event_async(struct urb *urb, struct uvc_video_chain *chain,
> > >
> > > --
> > > Regards,
> > >
> > > Laurent Pinchart
> >
> >
> >
> > --
> > Ricardo Ribalda
>
>
>
> --
> Ricardo Ribalda