linux-kernel - Re: [PATCH 1/2] cdc-acm: do not reset notification buffer index upon urb unlinking

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Message-ID: <1538659961.1254.2.camel@suse.com>
Date:   Thu, 04 Oct 2018 15:32:41 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Tobias Herzog <t-herzog@....de>
Cc:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH 1/2] cdc-acm: do not reset notification buffer index
 upon urb unlinking

On Sa, 2018-09-22 at 22:11 +0200, Tobias Herzog wrote:
> Resetting the write index of the notification buffer on urb unlink (e.g.
> closing a cdc-acm device from userspace) may lead to wrong interpretation
> of further received notifications, in case the index is not 0 when urb
> unlink happens (i.e. when parts of a notification already have been
> transferred). On the device side there is no "reset" of the notification
> transimission and thus we would get out of sync with the device.

Hi,

you are right, when you are describing the problem. The fix seems to me
to fix a part, albeit a large part of the issue. As far as I can tell,
the transfer could be partially succesful, meaning that the driver
loses a part in the middle of the notification.

	Regards
		Oliver