Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933444AbaDIO57 (ORCPT ); Wed, 9 Apr 2014 10:57:59 -0400 Received: from mga01.intel.com ([192.55.52.88]:62268 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932807AbaDIO55 (ORCPT ); Wed, 9 Apr 2014 10:57:57 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.97,826,1389772800"; d="scan'208";a="517557317" Message-ID: <53455FC6.7080009@intel.com> Date: Wed, 09 Apr 2014 22:57:10 +0800 From: Xiao Jin User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130106 Thunderbird/17.0.2 MIME-Version: 1.0 To: oneukum@suse.de, jhovold@gmail.com, gnomes@lxorguk.ukuu.org.uk CC: gregkh@linuxfoundation.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, david.a.cohen@linux.intel.com, yanmin.zhang@intel.com, jin.xiao@intel.com Subject: Re: [PATCH] cdc-acm: some enhancement on acm delayed write References: <53436770.9090008@intel.com> In-Reply-To: <53436770.9090008@intel.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Thanks all for the review. We meet with the problems when developing product. I would like to explain my understanding. On 04/08/2014 11:05 AM, Xiao Jin wrote: > > We find two problems on acm tty write delayed mechanism. > (1) When acm resume, the delayed wb will be started. But now > only one write can be saved during acm suspend. More acm write > may be abandoned. The scenario usually happened when user space write series AT after acm suspend. If acm accept the first AT, what's the reason for acm to refuse the second AT? If write return 0, user space will try repeatedly until resume. It looks simpler that acm accept all the data and sent out urb when resume. > (2) acm tty port ASYNCB_INITIALIZED flag will be cleared when > close. If acm resume callback run after ASYNCB_INITIALIZED flag > cleared, there will have no chance for delayed write to start. > That lead to acm_wb.use can't be cleared. If user space open > acm tty again and try to setd, tty will be blocked in > tty_wait_until_sent for ever. > We see tty write and close concurrently after acm suspend in this case. It looks no method to avoid it from tty layer. acm_tty_write and acm_resume call after acm_port_shutdown. It looks any action in acm_port_shutdown can't solve the problem. As acm has accepted the user space data, we can only find a way to send out urb. I feel anyway to discard the data looks like a lie to user space. In my understanding acm should accept data as much as possible, and send out urb as soon as possible. What do you think of? Br, Jin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/