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

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Message-ID: <8761h2nlk4.fsf@spindle.srvr.nix>
Date:	Fri, 05 Sep 2014 16:17:47 +0100
From:	Nix <nix@...eri.org.uk>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [3.16.1 REGRESSION]: Simtec Entropy Key (cdc-acm) broken in 3.16

On 5 Sep 2014, Oliver Neukum verbalised:

> On Fri, 2014-09-05 at 00:40 +0100, Nix wrote:
>> I'm working around this confusing morass by rebooting into each test
>> kernel, unplugging and replugging the entropy key if it was fubared,
>> then rebooting into the same kernel again and seeing if it was still
>> fubared. But this is not terribly fast, particularly not on a headless
>> compact-flash-based Geode box which doesn't even complete booting
>> without the entropy source which this bug cuts off :) so it'll be
>> sometime tomorrow before I can get this bisection done, I'm afraid.
>
> Ugh. My sympathies. I cannot suggest a better method, I am afraid.

Well, that method doesn't work. I've found pairs of kernels (e.g.
59a3d4c3631e553357b7305dc09db1990aa6757c and
b05d59dfceaea72565b1648af929b037b0f96d7f) where each kernel works on its
own (rebooting from that kernel into the same kernel keeps a working
key, so I would normally assume that each kernel is OK) but rebooting
from the first into the second yields a broken one if it was working
before (so one of them must, in fact, be broken, but I have no clue
which one).

So I can't figure out how to bisect this.

Any suggestions as to what failure-test I might use, or what other
methods I might use to figure out what's going wrong? Not knowing
anything about USB doesn't help here. I don't know for sure that this is
a cdc-acm problem -- bisecting just the cdc-acm driver was fruitless --
so it might be something more generally USBish.

-- 
NULL && (void)
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