From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754688Ab3CKUqD (ORCPT ); Mon, 11 Mar 2013 16:46:03 -0400 Received: from mailout01.c08.mtsvc.net ([205.186.168.189]:59170 "EHLO mailout01.c08.mtsvc.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754185Ab3CKUqA (ORCPT ); Mon, 11 Mar 2013 16:46:00 -0400 From: Peter Hurley To: Greg Kroah-Hartman , Jiri Slaby Cc: Sasha Levin , Dave Jones , Sebastian Andrzej Siewior , Shawn Guo , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, Peter Hurley Subject: [PATCH v5 05/44] tty: Remove unnecessary re-test of ldisc ref count Date: Mon, 11 Mar 2013 16:44:25 -0400 Message-Id: <1363034704-28036-6-git-send-email-peter@hurleysoftware.com> X-Mailer: git-send-email 1.8.1.2 In-Reply-To: <1363034704-28036-1-git-send-email-peter@hurleysoftware.com> References: <1361390599-15195-1-git-send-email-peter@hurleysoftware.com> <1363034704-28036-1-git-send-email-peter@hurleysoftware.com> X-Authenticated-User: 125194 peter@hurleysoftware.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Since the tty->ldisc is prevented from being changed by tty_set_ldisc() when a tty is being hung up, re-testing the ldisc user count is unnecessary -- ie, it cannot be a different ldisc and the user count cannot have increased (assuming the caller meets the precondition that TTY_LDISC flag is cleared) Removal of the 'early-out' locking optimization is necessary for the subsequent patch 'tty: Fix ldisc halt sequence on hangup'. Signed-off-by: Peter Hurley --- drivers/tty/tty_ldisc.c | 38 +++++++++++++++++++------------------- 1 file changed, 19 insertions(+), 19 deletions(-) diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index c5b848a..fa0170e 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -558,29 +558,29 @@ static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout) * have been halted for this to guarantee it remains idle. * * Caller must hold legacy and ->ldisc_mutex. + * + * NB: tty_set_ldisc() is prevented from changing the ldisc concurrently + * with this function by checking the TTY_HUPPING flag. */ static bool tty_ldisc_hangup_wait_idle(struct tty_struct *tty) { - while (tty->ldisc) { /* Not yet closed */ - if (atomic_read(&tty->ldisc->users) != 1) { - char cur_n[TASK_COMM_LEN], tty_n[64]; - long timeout = 3 * HZ; - tty_unlock(tty); - - while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) { - timeout = MAX_SCHEDULE_TIMEOUT; - printk_ratelimited(KERN_WARNING - "%s: waiting (%s) for %s took too long, but we keep waiting...\n", - __func__, get_task_comm(cur_n, current), - tty_name(tty, tty_n)); - } - /* must reacquire both locks and preserve lock order */ - mutex_unlock(&tty->ldisc_mutex); - tty_lock(tty); - mutex_lock(&tty->ldisc_mutex); - continue; + char cur_n[TASK_COMM_LEN], tty_n[64]; + long timeout = 3 * HZ; + + if (tty->ldisc) { /* Not yet closed */ + tty_unlock(tty); + + while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) { + timeout = MAX_SCHEDULE_TIMEOUT; + printk_ratelimited(KERN_WARNING + "%s: waiting (%s) for %s took too long, but we keep waiting...\n", + __func__, get_task_comm(cur_n, current), + tty_name(tty, tty_n)); } - break; + /* must reacquire both locks and preserve lock order */ + mutex_unlock(&tty->ldisc_mutex); + tty_lock(tty); + mutex_lock(&tty->ldisc_mutex); } return !!tty->ldisc; } -- 1.8.1.2