Received-SPF: pass (google.com: domain of linux-kernel+bounces-144947-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
From: =?utf-8?Q?Bj=C3=B8rn_Mork?= <bjorn@mork.no>
To: Oliver Neukum <oneukum@suse.com>
Cc: Aleksander Morgado <aleksandermj@chromium.org>, linux-usb@vger.kernel.org,
        gregkh@linuxfoundation.org, linux@roeck-us.net,
        linux-kernel@vger.kernel.org, ejcaruso@chromium.org
Subject: Re: [PATCH] usb: cdc-wdm: close race between read and workqueue
Organization: m
References: <385a3519-b45d-48c5-a6fd-a3fdb6bec92f@chromium.org>
	<87mspvi0lk.fsf@miraculix.mork.no>
	<a6ad34d3-9cce-4178-8271-0e09ced2b6f4@suse.com>
	<878r1fht93.fsf@miraculix.mork.no>
	<c35f98be-23a3-41c3-bee5-f394ce504545@suse.com>
Date: Mon, 15 Apr 2024 12:53:31 +0200
In-Reply-To: <c35f98be-23a3-41c3-bee5-f394ce504545@suse.com> (Oliver Neukum's
	message of "Mon, 15 Apr 2024 12:14:48 +0200")
Message-ID: <8734rmj3ro.fsf@miraculix.mork.no>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux)
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable

Oliver Neukum <oneukum@suse.com> writes:
> On 15.04.24 11:26, Bj=C3=B8rn Mork wrote:
>> Oliver Neukum <oneukum@suse.com> writes:
>>> On 15.04.24 08:47, Bj=C3=B8rn Mork wrote:
>>>
>>>> urb from service_outstanding_interrupt(). That's why it was added. See
>>>> the explanation Robert wrote when introducing it:
>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/com=
mit/drivers/usb/class/cdc-wdm.c?id=3Dc1da59dad0ebd3f9bd238f3fff82b1f7ffda78=
29
>>>
>>> Well, the explanation is correct in that we must read
>>> data available. However, if the RESPONDING flag is set
>>> and the URB submitted, we are already doing so.
>> Sounds reasonable.  Except that the bug proves we didn't.
>
> Why? I am afraid I do not get that part.

I don't get how it happens either.  But that's the only thing changed by
the patch.

>  > If you are right that service_outstanding_interrupt can race
>   againts
>> itself (and I don't doubt that), then I guess this could also happen
>> between failure to submit the URB and clearing the flag?
>
> Yes, it can. In fact in this case the behavior should not change.
> I am afraid we have a misunderstanding. It seems to me that in the
> unchanged driver the result of service_outstanding_interrupt()
> is undefined.
> Please explain.

Sorry, I am so lost here that I am probably only confusing things.  I do
not understand why we unlock &desc->iuspin around the usb_submit_urb
call.  And git tells me I wrote that.


Bj=C3=B8rn