linux-kernel - [PATCH v3 21/23] tty: Re-parent orphaned tty_set

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Message-Id: <1360095638-6624-22-git-send-email-peter@hurleysoftware.com>
Date:	Tue,  5 Feb 2013 15:20:36 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alan Cox <alan@...ux.intel.com>, Jiri Slaby <jslaby@...e.cz>,
	Sasha Levin <levinsasha928@...il.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ilya Zykov <ilya@...x.ru>, Dave Jones <davej@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH v3 21/23] tty: Re-parent orphaned tty_set_ldisc() comments


Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
 drivers/tty/tty_ldisc.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 92629c1..49e4825 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -545,10 +545,18 @@ static int tty_ldisc_halt(struct tty_struct *tty, struct tty_struct *o_tty,
 {
 	int scheduled, o_scheduled, retval;
 
+	/*
+	 *	The TTY_LDISC bit prevents anyone taking an ldisc
+	 *	reference once it is clear.
+	 */
 	clear_bit(TTY_LDISC, &tty->flags);
 	if (o_tty)
 		clear_bit(TTY_LDISC, &o_tty->flags);
 
+	/*
+	 *	Make sure we don't change while someone holds a
+	 *	reference to the line discipline.
+	 */
 	retval = tty_ldisc_wait_idle(tty, timeout);
 	if (!retval && o_tty)
 		retval = tty_ldisc_wait_idle(o_tty, timeout);
@@ -702,13 +710,9 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 	o_ldisc = tty->ldisc;
 
 	tty_unlock(tty);
+
 	/*
-	 *	Make sure we don't change while someone holds a
-	 *	reference to the line discipline. The TTY_LDISC bit
-	 *	prevents anyone taking a reference once it is clear.
-	 *	We need the lock to avoid racing reference takers.
-	 *
-	 *	We must clear the TTY_LDISC bit here to avoid a livelock
+	 *	We must halt the line discipline here to avoid a livelock
 	 *	with a userspace app continually trying to use the tty in
 	 *	parallel to the change and re-referencing the tty.
 	 */
-- 
1.8.1.2

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