From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 65F59C43387 for ; Fri, 11 Jan 2019 19:33:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3E6B5218D4 for ; Fri, 11 Jan 2019 19:33:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1547235191; bh=WsNfx33BzIsjnY5yiFog9pEDVAqaiJ1DB5eYd1qgUdA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=Jv8rwbRAetUPS+QeKebiKVhERY3s8REgGPOE6DjftRMkQAUaQ9+2LMV8BjvPIPtRA mL80wL8tCVuh4wGZ28L8iFntfk2uveq+ur05tdHttLM4pO0iNkobEV0QHrVXwpDt7S sg24vBEx502SBoYDTfh7aUBHR66P3UjyvJQVJzPU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388658AbfAKTdI (ORCPT ); Fri, 11 Jan 2019 14:33:08 -0500 Received: from mail.kernel.org ([198.145.29.99]:33598 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388593AbfAKTdC (ORCPT ); Fri, 11 Jan 2019 14:33:02 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4468C218C3; Fri, 11 Jan 2019 19:33:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1547235181; bh=WsNfx33BzIsjnY5yiFog9pEDVAqaiJ1DB5eYd1qgUdA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=PyPsXlSjGuj6393JasHvCtv+SI2rh3+81KfdhlJVXQ0QJeOF6bDlJ1r+4NoHKvAUJ eHJmPlkfyBmxMfprhj3nms5+fYXNRHuEkDMV64ScGKSd5KRN/RyOo1mr0H5wL9D2Zk rp3OnGi9Dv9gA7/68wcqngVaXRL6EFIZKgXwwGIE= Date: Fri, 11 Jan 2019 20:32:59 +0100 From: Greg Kroah-Hartman To: Nicolas Pitre Cc: Dmitry Safonov , Jiri Slaby , Mark Rutland , Tetsuo Handa , Tycho Andersen , Dave Mielke , linux-kernel@vger.kernel.org Subject: Re: commit 83d817f410 broke my ability to use Linux with a braille display Message-ID: <20190111193259.GA14966@kroah.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.2 (2019-01-07) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 11, 2019 at 01:33:09PM -0500, Nicolas Pitre wrote: > I use Linux with the help of a braille display and the brltty daemon. It > turns out that the latest mainline kernel I can work with comes from > commit 231f8fd0cc. Anything past that and I lose the ability to read the > console barely a few seconds after the system has booted as brltty is > thrown a wrench and the braille display becomes completely inoperable. > > Things get somewhat better with commit c96cf923a9 as brltty is not > longer incapacitated, but some programs would randomly crash. Even the > very first login attempt won't work as I soon as I hit enter after my > user name the password prompt is skipped over, just like if the enter > key had been hit twice. Then lynx (the text web browser) would crash as > soon as I switch the virtual console with LeftAlt+FN. Mind you, this > isn't easy to perform bisection in those conditions. > > And the worst commit i.e. 83d817f410 is marked for stable! :-( > > Some interaction with brltty must be at play here otherwise such > breakage would never have survived up to the mainline kernel. > > As far as latest mainline is concerned, I managed to reproduce at least > one of the unwelcome behavior change (hoping that's all there is to this > issue) with a very simple test case so you won't have to learn braille > to debug this: > > # from any vt, make sure tty40 is allocated and empty > openvt -c 40 -f -- true > > # open it and wait on read() > cat /dev/tty40 > > # from a second vt, simply open tty40 again > true < /dev/tty40 > > # come back to the first vt and watch cat bailing out with EAGAIN. > > Please fix. Please try the patch below, it was just queued up to my tree and should resolve the issue. If not, please let us know. thanks, greg k-h >From d3736d82e8169768218ee0ef68718875918091a0 Mon Sep 17 00:00:00 2001 From: Dmitry Safonov Date: Wed, 9 Jan 2019 01:17:40 +0000 Subject: tty: Don't hold ldisc lock in tty_reopen() if ldisc present Try to get reference for ldisc during tty_reopen(). If ldisc present, we don't need to do tty_ldisc_reinit() and lock the write side for line discipline semaphore. Effectively, it optimizes fast-path for tty_reopen(), but more importantly it won't interrupt ongoing IO on the tty as no ldisc change is needed. Fixes user-visible issue when tty_reopen() interrupted login process for user with a long password, observed and reported by Lukas. Fixes: c96cf923a98d ("tty: Don't block on IO when ldisc change is pending") Fixes: 83d817f41070 ("tty: Hold tty_ldisc_lock() during tty_reopen()") Cc: Jiri Slaby Reported-by: Lukas F. Hartmann Tested-by: Lukas F. Hartmann Cc: stable Signed-off-by: Dmitry Safonov Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_io.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index bfe9ad85b362..23c6fd238422 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -1256,7 +1256,8 @@ static void tty_driver_remove_tty(struct tty_driver *driver, struct tty_struct * static int tty_reopen(struct tty_struct *tty) { struct tty_driver *driver = tty->driver; - int retval; + struct tty_ldisc *ld; + int retval = 0; if (driver->type == TTY_DRIVER_TYPE_PTY && driver->subtype == PTY_TYPE_MASTER) @@ -1268,13 +1269,18 @@ static int tty_reopen(struct tty_struct *tty) if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN)) return -EBUSY; - retval = tty_ldisc_lock(tty, 5 * HZ); - if (retval) - return retval; + ld = tty_ldisc_ref_wait(tty); + if (ld) { + tty_ldisc_deref(ld); + } else { + retval = tty_ldisc_lock(tty, 5 * HZ); + if (retval) + return retval; - if (!tty->ldisc) - retval = tty_ldisc_reinit(tty, tty->termios.c_line); - tty_ldisc_unlock(tty); + if (!tty->ldisc) + retval = tty_ldisc_reinit(tty, tty->termios.c_line); + tty_ldisc_unlock(tty); + } if (retval == 0) tty->count++; -- 2.20.1