linux-kernel - Re: [3.16.1 BISECTED REGRESSION]: Simtec Entropy Key (cdc-acm) broken in 3.16

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Date:	Fri, 24 Oct 2014 13:14:42 +0200
From:	Johan Hovold <johan@...nel.org>
To:	Nix <nix@...eri.org.uk>
Cc:	Johan Hovold <johan@...nel.org>, Paul Martin <pm@...ian.org>,
	Daniel Silverstone <dsilvers@...ian.org>,
	Oliver Neukum <oliver@...kum.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [3.16.1 BISECTED REGRESSION]: Simtec Entropy Key (cdc-acm)
 broken in 3.16

[ +CC: linux-usb ]

On Wed, Oct 22, 2014 at 04:36:59PM +0100, Nix wrote:
> On 22 Oct 2014, Johan Hovold outgrape:
> 
> > On Wed, Oct 22, 2014 at 10:31:17AM +0100, Nix wrote:
> >> On 14 Oct 2014, Johan Hovold verbalised:
> >> 
> >> > On Sun, Oct 12, 2014 at 10:36:30PM +0100, Nix wrote:
> >> >> I have checked: this code is being executed against a symlink that
> >> >> points to /dev/ttyACM0, and the tcsetattr() succeeds. (At least, it's
> >> >> succeeding on the kernel I'm running now, but of course that's 3.16.5
> >> >> with this commit reverted...)
> >> >
> >> > You could verify that by enabling debugging in the cdc-acm driver and
> >> > making sure that the corresponding control messages are indeed sent on
> >> > close.
> >> 
> >> I have a debugging dump at
> >> <http://www.esperi.org.uk/~nix/temporary/cdc-acm.log>; it's fairly
> >
> > What kernel were you using here? The log seems to suggest that it was
> > generated with the commit in question reverted.
> 
> Look now :) (the previous log is still there in cdc-acm-reverted.log.)

Unfortunately, it seems the logs are incomplete. There are lots of
entries missing (e.g. "acm_tty_install" when opening, but also some
"acm_submit_read_urb"), some of which were there in your first log.

Also you can disable the "acm_tty_write - count" output, which isn't
really useful here.

> This contains two boots -- one on which the USB key worked, and the next
> (with an identical kernel) with which the key was broken. (I'm not sure
> whether this problem happens at startup or shutdown time, so it seemed
> best to provide both.)

That's a good idea.

Is it only after reboot you've seen the device fail? What if you
physically disconnect and reconnect the device instead, or simply
repeatedly open and close it?

Johan
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