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

[Michael Grzeschik <mgr@pengutronix.de>]

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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?

Michael

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