From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752869Ab3CEXOv (ORCPT ); Tue, 5 Mar 2013 18:14:51 -0500 Received: from mailout01.c08.mtsvc.net ([205.186.168.189]:57286 "EHLO mailout01.c08.mtsvc.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751163Ab3CEXOt (ORCPT ); Tue, 5 Mar 2013 18:14:49 -0500 Message-ID: <1362525272.18799.165.camel@thor.lan> Subject: Re: [PATCH v3 00/23] ldisc fixes From: Peter Hurley To: Jiri Slaby Cc: Felipe Balbi , Sebastian Andrzej Siewior , Greg Kroah-Hartman , Sasha Levin , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org Date: Tue, 05 Mar 2013 18:14:32 -0500 In-Reply-To: <51367433.4060408@suse.cz> References: <1355509370-5883-1-git-send-email-peter@hurleysoftware.com> <1360095638-6624-1-git-send-email-peter@hurleysoftware.com> <20130305205033.GA5771@linutronix.de> <1362522029.18799.145.camel@thor.lan> <51367433.4060408@suse.cz> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.6.3-0pjh1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Authenticated-User: 125194 peter@hurleysoftware.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [now this discussion has turned to usb gadget +cc Felipe Balbi, linux-usb, -cc Dave Jones, Ilya Zykov] On Tue, 2013-03-05 at 23:39 +0100, Jiri Slaby wrote: > On 03/05/2013 11:20 PM, Peter Hurley wrote: > > [--cc Alan Cox] > > > > On Tue, 2013-03-05 at 21:50 +0100, Sebastian Andrzej Siewior wrote: > >> * Peter Hurley | 2013-02-05 15:20:15 [-0500]: > >> > >>> Please re-test with your dummy_hcd/g_nokia testcase, although > >>> I'm not convinced that usb gadget is using tty_hangup() appropriately. > >>> tty drivers use this for async carrier loss coming from an IRQ > >>> which will be disabled if the tty has been shutdown. Does gserial > >>> prevent async hangup to a dead tty in a similar fashion? > >> > >> Not sure I understood. tty_hangup() is only called from within > >> gserial_disconnect() which calls right after usb_ep_disable(). After > >> usb_ep_disable() no further serial packets can be received until the > >> endpoints are re-enabled. This happens in gserial_connect(). > > > > That's why I asked. There are two potential issues: > > > > First, tty_hangup() is asynchronous -- ie., it returns immediately. It > > does not wait for the tty device to actually perform the hangup. So if > > the gadget layers start cleanup immediately after, expecting that they > > won't get a flurry of tty calls, that would be bad. > > Sorry, I missed what driver is this? g_serial. drivers/usb/gadget/u_serial.c > > tty_vhangup() is synchronous -- ie., you wait while it cleans up. This > > is what the usb serial core does on it's disconnect() method. But I > > didn't research further if the circumstances were the same. > > Even when tty_vhangup returns, it does not guarantee a closed tty. And > it also does not guarantee that any of tty->ops won't be called. The > latter is true only for devices that can be consoles. (For those, > file->ops are not redirected.) In that case one needs to wait for > port->count to become 0. Perhaps I was oversimplifying. But my point was I doubt usb gadget is conducting its teardown safely wrt tty. Regards, Peter Hurley