From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758251AbaGWQE2 (ORCPT ); Wed, 23 Jul 2014 12:04:28 -0400 Received: from mailout32.mail01.mtsvc.net ([216.70.64.70]:44857 "EHLO n23.mail01.mtsvc.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1757646AbaGWQE0 (ORCPT ); Wed, 23 Jul 2014 12:04:26 -0400 Message-ID: <53CFDD05.4010104@hurleysoftware.com> Date: Wed, 23 Jul 2014 12:04:21 -0400 From: Peter Hurley User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: "xinhui.pan" CC: Greg KH , mnipxh , jslaby@suse.cz, linux-kernel@vger.kernel.org, yanmin_zhang@linux.intel.com Subject: Re: [PATCH] tty/tty_io.c: make a check before reuse cdev References: <53CD0BD4.4050007@gmail.com> <20140721153840.GA6802@kroah.com> <53CE5097.2000502@intel.com> <53CE941B.1030102@hurleysoftware.com> <53CF7EAC.8010201@intel.com> In-Reply-To: <53CF7EAC.8010201@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Authenticated-User: 990527 peter@hurleysoftware.com X-MT-ID: 8FA290C2A27252AACF65DBC4A42F3CE3735FB2A4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Xinhui, On 07/23/2014 05:21 AM, xinhui.pan wrote: > 于 2014年07月23日 00:40, Peter Hurley 写道: >> On 07/22/2014 07:52 AM, xinhui.pan wrote: >>> 于 2014年07月21日 23:38, Greg KH 写道: >>>> On Mon, Jul 21, 2014 at 08:47:16PM +0800, pp wrote: >>>>> tty driver register its device and (D)init the cdevs again. >>>> >>>> What driver does this with an "old" device, it should have created a new >>>> one, otherwise, as you have pointed out, it's a bug. >>>> >>> >>> I can't agree more with you. we should not use "old" device. >> >> This is a gsm driver problem. The GSM driver is reusing device indexes >> for still-open ttys. >> >> The GSM driver uses a global table, gsm_mux[], to allocate device indexes >> but prematurely clears the table entry in gsm_mux_cleanup(). If instead, >> clearing the gsm_mux table entry were deferred to gsm_mux_free(), then >> device indexes would not be getting reused until after the last tty >> associated with the last gsm attach was closed. >> > > Very nice solution. We will check if this can cause any risk, both to kernel and user space. > Using a new tty base to register with new cdevs may give us more chance to wait PROCESS quit/close. > when total 256 tty used up, what we should do is still in discuss. I saw your patch for the use of gsm->num before gsm_activate_mux() has allocated the table entry; thanks for fixing that. As for what to do if all the gsm_mux table entries are used: if the error is infrequent, I suggest simply returning an error which is what the driver does currently. Otherwise, a more dynamic allocation scheme may be required. I did notice while reviewing the error handling that gsmld_open() will leak the entire composite ldisc data allocated by gsm_alloc_mux() if gsmld_attach_gsm() fails. Regards, Peter Hurley