From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758928AbcHDRpc (ORCPT ); Thu, 4 Aug 2016 13:45:32 -0400 Received: from bhuna.collabora.co.uk ([46.235.227.227]:32921 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758969AbcHDRp3 (ORCPT ); Thu, 4 Aug 2016 13:45:29 -0400 Subject: Re: [PACTH v1] cdc-wdm: Clear read pipeline in case of error To: Oliver Neukum References: <1469729992-6228-1-git-send-email-robert.foss@collabora.com> <1470140595.30985.20.camel@suse.com> <04ca38d7-6538-d220-3fe7-7ece503ce4ad@collabora.com> <1470146394.30985.25.camel@suse.com> <1470220742.4612.7.camel@suse.com> Cc: pprabhu@chromium.org, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, Guenter Roeck , Ben Chan From: Robert Foss Message-ID: <1775d53f-0129-4e94-b08c-7d4c58fa9fa6@collabora.com> Date: Thu, 4 Aug 2016 13:44:29 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: <1470220742.4612.7.camel@suse.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2016-08-03 06:39 AM, Oliver Neukum wrote: > On Tue, 2016-08-02 at 10:37 -0400, Robert Foss wrote: >> >> On 2016-08-02 09:59 AM, Oliver Neukum wrote: >>> On Tue, 2016-08-02 at 09:54 -0400, Robert Foss wrote: >>>> >>>> On 2016-08-02 08:23 AM, Oliver Neukum wrote: >>>>> On Thu, 2016-07-28 at 14:19 -0400, robert.foss@collabora.com wrote: >>>>>> From: Prathmesh Prabhu >>>>>> >>>>>> Implemented queued response handling. This queue is processed every >>>>>> time the >>>>>> WDM_READ flag is cleared. >>>>>> >>>>>> In case of a read error, userspace may not actually read the data, >>>>>> since the >>>>>> driver returns an error through wdm_poll. After this, the underlying >>>>>> device may >>>>>> attempt to send us more data, but the queue is not processed. While >>>>>> userspace is >>>>>> also blocked, because the read error is never cleared. >>>>> >>>>> Could you explain why user space cannot just read more data? >>>>> That will clear the error. >>>> >>>> Userspace certainly could read more data, but for the case when >>>> userspace doesn't read and clear a potential an error, we still would >>>> like to not be stuck if the device sends more data. space >>>> >>>> I hope that answers your question, if not I'll try to be more elaborate. >>> >>> Clear, but why does that require the suppression of an error condition? >>> errors should always be delivered. >> >> The goal is not to clear the error condition, but that is required to >> not stay stuck. > > How can that depend on what we return to user space? > In the driver we can continue just ignoring errors. > Now, if user space stops reading because we reported an error, > that is the decision user space has made. We cannot ignore errors > in the kernel because we don't like what user space does when it > sees the error. So perhaps the better solution is to be more intelligent about how desc->rerr is written to during after an error to be able to maintain the error condition? > > Regards > Oliver > >