linux-kernel - Re: USB autosuspend vs. URB submission

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Message-ID: <CACVXFVNUJ8i5hOX8oqcBn1rO=KmHQU3WMBVBh9HF=BfJw1QcPw@mail.gmail.com>
Date:	Thu, 10 Jan 2013 13:13:58 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	Josh Boyer <jwboyer@...hat.com>,
	Alan Stern <stern@...land.harvard.edu>,
	gregkh@...uxfoundation.org, mdharm-usb@...-eyed-alien.net,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: USB autosuspend vs. URB submission

On Thu, Jan 10, 2013 at 7:05 AM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> I've never heard of such problems with the uvcvideo driver, and I don't see
> anything wrong with the code at first sight. The driver only submits URBs when

IMO, there is a minor fault in the error handling path of
uvc_status_start() inside uvc_v4l2_open(), and the 'users' count
should have been decreased before usb_autopm_put_interface().
In theory, the warning can be triggered when the device is
opened just between usb_autopm_put_interface() and
atomic_dec(&stream->dev->users), but I don't think it is
the cause of the report.

> starting the video capture (at that point no URB should be in flight) or in
> the URB completion handler (by definition the URB has completed then).
>
> I've had a quick look at the trace posted at
> https://bugzilla.redhat.com/show_bug.cgi?id=879462 but usbmon only shows URBs
> that are successfully submitted. I'm not sure what useful information I could
> get from the trace.

It might be useful to post the relevant 'dmesg' and the usbmon together.

Thanks,
-- 
Ming Lei
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