From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755477Ab3CEWUt (ORCPT ); Tue, 5 Mar 2013 17:20:49 -0500 Received: from mailout01.c08.mtsvc.net ([205.186.168.189]:53488 "EHLO mailout01.c08.mtsvc.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755104Ab3CEWUs (ORCPT ); Tue, 5 Mar 2013 17:20:48 -0500 Message-ID: <1362522029.18799.145.camel@thor.lan> Subject: Re: [PATCH v3 00/23] ldisc fixes From: Peter Hurley To: Sebastian Andrzej Siewior Cc: Greg Kroah-Hartman , Jiri Slaby , Sasha Levin , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Ilya Zykov , Dave Jones Date: Tue, 05 Mar 2013 17:20:29 -0500 In-Reply-To: <20130305205033.GA5771@linutronix.de> References: <1355509370-5883-1-git-send-email-peter@hurleysoftware.com> <1360095638-6624-1-git-send-email-peter@hurleysoftware.com> <20130305205033.GA5771@linutronix.de> 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 [--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. 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. Second, when the hangup actually does run -- in __tty_hangup() -- it expects the tty to exist. I didn't go looking through the gadget layers to see if the tty was disposed some other way, which might race the asynchronous tty hangup. Thanks, Peter Hurley