Re: [PATCH v4] usb: gadget: uvc: increase worker prio to WQ_HIGHPRI

[Nathan Chancellor <nathan@kernel.org>]

On Wed, Sep 28, 2022 at 09:45:29PM +0200, Michael Grzeschik wrote:
> Hi Nathan!
> 
> On Wed, Sep 28, 2022 at 09:29:55AM -0700, Nathan Chancellor wrote:
> > On Wed, Sep 07, 2022 at 11:58:18PM +0200, Michael Grzeschik wrote:
> > > This patch is changing the simple workqueue in the gadget driver to be
> > > allocated as async_wq with a higher priority. The pump worker, that is
> > > filling the usb requests, will have a higher priority and will not be
> > > scheduled away so often while the video stream is handled. This will
> > > lead to fewer streaming underruns.
> > > 
> > > Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
> > 
> > ...
> > 
> > > diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
> > > index 58e383afdd4406..1a31e6c6a5ffb8 100644
> > > --- a/drivers/usb/gadget/function/uvc.h
> > > +++ b/drivers/usb/gadget/function/uvc.h
> > > @@ -88,6 +88,7 @@ struct uvc_video {
> > >  	struct usb_ep *ep;
> > > 
> > >  	struct work_struct pump;
> > > +	struct workqueue_struct *async_wq;
> > > 
> > >  	/* Frame parameters */
> > >  	u8 bpp;
> > 
> > I am commenting here because this is the most recent change but after
> > this showed up in -next as commit 9b91a6523078 ("usb: gadget: uvc:
> > increase worker prio to WQ_HIGHPRI"), I see the following warning/error
> > when building s390 allmodconfig:
> > 
> >  In file included from ../include/linux/string.h:253,
> >                   from ../include/linux/bitmap.h:11,
> >                   from ../include/linux/cpumask.h:12,
> >                   from ../include/linux/smp.h:13,
> >                   from ../include/linux/lockdep.h:14,
> >                   from ../include/linux/rcupdate.h:29,
> >                   from ../include/linux/rculist.h:11,
> >                   from ../include/linux/pid.h:5,
> >                   from ../include/linux/sched.h:14,
> >                   from ../include/linux/ratelimit.h:6,
> >                   from ../include/linux/dev_printk.h:16,
> >                   from ../include/linux/device.h:15,
> >                   from ../drivers/usb/gadget/function/f_uvc.c:9:
> >  In function ‘fortify_memset_chk’,
> >      inlined from ‘uvc_register_video’ at ../drivers/usb/gadget/function/f_uvc.c:424:2:
> >  ../include/linux/fortify-string.h:301:25: error: call to ‘__write_overflow_field’ declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
> >    301 |                         __write_overflow_field(p_size_field, size);
> >        |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > 
> > This commit did not directly cause this, it just made the issue more
> > obvious. In commit e4ce9ed835bc ("usb: gadget: uvc: ensure the vdev is
> > unset"), also authored by you, the size parameter appears to be wrong?
> > It is using the size of 'struct uvc_video', instead of the size of
> > 'struct video_device'. It appears to be pure luck that everything worked
> > up until this point, as those two types had the same size (1400 bytes)
> > before this change but now 'struct uvc_video' is 1408 bytes, meaning
> > there is now an overwrite. Any reason this is not the fix?
> > 
> > Cheers,
> > Nathan
> > 
> > diff --git a/drivers/usb/gadget/function/f_uvc.c b/drivers/usb/gadget/function/f_uvc.c
> > index e6948cf8def3..836601227155 100644
> > --- a/drivers/usb/gadget/function/f_uvc.c
> > +++ b/drivers/usb/gadget/function/f_uvc.c
> > @@ -421,7 +421,7 @@ uvc_register_video(struct uvc_device *uvc)
> > 	int ret;
> > 
> > 	/* TODO reference counting. */
> > -	memset(&uvc->vdev, 0, sizeof(uvc->video));
> > +	memset(&uvc->vdev, 0, sizeof(uvc->vdev));
> > 	uvc->vdev.v4l2_dev = &uvc->v4l2_dev;
> > 	uvc->vdev.v4l2_dev->dev = &cdev->gadget->dev;
> > 	uvc->vdev.fops = &uvc_v4l2_fops;
> > 
> 
> This sounds right. Do you send a proper patch?

Yup, I sent

https://lore.kernel.org/20220928201921.3152163-1-nathan@kernel.org/

which should be in your mailbox now :)

Cheers,
Nathan