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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,USER_AGENT_GIT 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 8FECCC2F3BE for ; Mon, 21 Jan 2019 13:55:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5AB7920879 for ; Mon, 21 Jan 2019 13:55:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548078939; bh=BPo/BOGj/ioXB67XrTTeURLxsdTnp5tGJljFcx8auHE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=WCwcLlUO1pI6Ab3e8/HE8GXlaw8uoR3G/8f03wxneoQAwXj+yBJEcYSkh84cT2Uz0 Iq9FOjYDuxeyYsLR1izfQ0HcvAvweDRk3iGBpvZddCBh9/KFACyRZGa6K+RmLYgaHz OWKg57VKWEERAhMGpQt40PoUpbhGkEWft1WGFLq8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731308AbfAUNzf (ORCPT ); Mon, 21 Jan 2019 08:55:35 -0500 Received: from mail.kernel.org ([198.145.29.99]:40238 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731733AbfAUNzb (ORCPT ); Mon, 21 Jan 2019 08:55:31 -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 3BF3520861; Mon, 21 Jan 2019 13:55:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548078930; bh=BPo/BOGj/ioXB67XrTTeURLxsdTnp5tGJljFcx8auHE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=XXvlMYb1zG9p770w4EUHlXVr/PnV1kMNro83ShR5vmWkgV01k4QCOfzFPDOzFQoi8 8IoEktS4PO0km3RTBX4Ojd19PRXmLToQ8TsXbvN+0VcobB6WrHaQ70QXzAnJNREqoK 6IQ0d1KR/WhTKqbafDgwKS1fvDMpGgLH+fEiU9kk= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jiri Slaby , "Lukas F. Hartmann" , Dmitry Safonov Subject: [PATCH 4.9 04/51] tty: Dont hold ldisc lock in tty_reopen() if ldisc present Date: Mon, 21 Jan 2019 14:44:00 +0100 Message-Id: <20190121122453.967865420@linuxfoundation.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190121122453.700446926@linuxfoundation.org> References: <20190121122453.700446926@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Dmitry Safonov commit d3736d82e8169768218ee0ef68718875918091a0 upstream. 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 | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-) --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -1475,7 +1475,8 @@ static void tty_driver_remove_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) @@ -1487,13 +1488,18 @@ static int tty_reopen(struct tty_struct if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN)) return -EBUSY; - 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); + 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 (retval == 0) tty->count++;