linux-kernel - [PATCH -next v2 10/26] tty: Don't take tty

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Date:	Wed,  5 Nov 2014 12:12:53 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Jiri Slaby <jslaby@...e.cz>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH -next v2 10/26] tty: Don't take tty_mutex for tty count changes

Holding tty_mutex is no longer required to serialize changes to
the tty_count or to prevent concurrent opens of closing ttys;
tty_lock() is sufficient.

Reviewed-by: Alan Cox <alan@...ux.intel.com>
Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
 drivers/tty/tty_io.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 49167ed..f1c4b07 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1806,10 +1806,6 @@ int tty_release(struct inode *inode, struct file *filp)
 	 * each iteration we avoid any problems.
 	 */
 	while (1) {
-		/* Guard against races with tty->count changes elsewhere and
-		   opens on /dev/tty */
-
-		mutex_lock(&tty_mutex);
 		tty_lock_pair(tty, o_tty);
 		tty_closing = tty->count <= 1;
 		o_tty_closing = o_tty &&
@@ -1845,7 +1841,6 @@ int tty_release(struct inode *inode, struct file *filp)
 			       __func__, tty_name(tty, buf));
 		}
 		tty_unlock_pair(tty, o_tty);
-		mutex_unlock(&tty_mutex);
 		schedule_timeout_killable(timeout);
 		if (timeout < 120 * HZ)
 			timeout = 2 * timeout + 1;
@@ -1900,7 +1895,6 @@ int tty_release(struct inode *inode, struct file *filp)
 		read_unlock(&tasklist_lock);
 	}
 
-	mutex_unlock(&tty_mutex);
 	tty_unlock_pair(tty, o_tty);
 	/* At this point, the tty->count == 0 should ensure a dead tty
 	   cannot be re-opened by a racing opener */
-- 
2.1.3

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