From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757331Ab1LWPFr (ORCPT ); Fri, 23 Dec 2011 10:05:47 -0500 Received: from mx2.compro.net ([12.186.155.4]:62788 "EHLO mx2.compro.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752558Ab1LWPFo (ORCPT ); Fri, 23 Dec 2011 10:05:44 -0500 X-Greylist: delayed 846 seconds by postgrey-1.27 at vger.kernel.org; Fri, 23 Dec 2011 10:05:44 EST X-IronPort-AV: E=Sophos;i="4.71,399,1320642000"; d="scan'208";a="7421546" Message-ID: <4EF49579.9040907@compro.net> Date: Fri, 23 Dec 2011 09:51:37 -0500 From: Mark Hounschell Reply-To: markh@compro.net Organization: Compro Computer Svcs. User-Agent: Mozilla/5.0 (X11; Linux i686; rv:8.0) Gecko/20111105 Thunderbird/8.0 MIME-Version: 1.0 To: Linux-kernel CC: Mark Hounschell Subject: tty TTY_HUPPED anomaly 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 I have an application that has seemingly been stable for many years and even using the 3.1.1 kernel all is fine. I'm using the openSuSE distribution. All is good with the openSuSE-11.4 dist and the 3.1.1 kernel. We recently started testing this application on openSuSE-12.1 using the same vanilla 3.1.1 kernel and now we have problems with just about all out tty/serial related devices that we use. I thought the problem maybe an openSuSE glibc problem so I built and ran the openSuSE-12.1 version of glibc on the openSuSE-11.4 dist but the application worked just fine. So I started looking at the kernel and one of our serial devices that fails. I choose the Synclink GT because its driver is "in kernel". In our application with this particular card, the following TIOCSETD ioctl is this code snippet fails most of the time. int32_t hdlc_disc = N_HDLC; Q->fd = open(Q->FileName, (O_RDWR | O_NONBLOCK), 0); if (Q->fd < 0) return (FALSE); Q->File = fdopen(Q->fd, "rw"); fcntl(Q->fd, F_SETFL, fcntl(S->fd,F_GETFL) & ~O_NONBLOCK); if (ioctl(Q->fd, TIOCSETD, &hdlc_disc) < 0) { perror("SCM_open_port: TIOCSETD failed: "); return (FALSE); } The kernel code that results in the above code snippet failure is the following section of the tty_set_ldisc function in tty_io.c. if (test_bit(TTY_HUPPED, &tty->flags)) { /* We were raced by the hangup method. It will have stomped the ldisc data and closed the ldisc down */ clear_bit(TTY_LDISC_CHANGING, &tty->flags); mutex_unlock(&tty->ldisc_mutex); tty_ldisc_put(new_ldisc); tty_unlock(); return -EIO; } I do not really understand what TTY_HUPPED is or how it could be getting set. I look at it when the tty_set_ldisc function is entered and it is not set. Some where between entrance of the tty_set_ldisc and getting to the above code TTY_HUPPED gets set causing the -EIO return. I see nothing in my code that should cause this to happen. At start up time a thread for each port used does this then goes to sleep. Again, I can't understand why now with openSuSE-12.1 this starts happening. Can someone help me understand why this might happen. I don't know if it is me, the dist, or the kernel. Frequently it all works at startup and will eventually fail during operation. Other serial cards that I also have similar problems with (different ioctls) are various Digi serial cards. I haven't look into the kernel to see what is happening with those as yet but am sure the problem is related. Sometimes they work, most of the time they do not. Many thanks in advance Mark