patch "Revert "tty: pty: Fix race condition between release_one_tty and" added to tty-testing

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    Revert "tty: pty: Fix race condition between release_one_tty and

to my tty git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-testing branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will be merged to the tty-next branch sometime soon,
after it passes testing, and the merge window is open.

If you have any questions about this process, please let me know.


From 0eae4686a128d87503863a261e84887750c8bc68 Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: Fri, 29 Mar 2019 15:47:40 +0100
Subject: Revert "tty: pty: Fix race condition between release_one_tty and
 pty_write"

This reverts commit b9ca5f8560af244489b4a1bc1ae88b341f24bc95 as 0-day
shows it has a circular locking dependency.

Fixes: b9ca5f8560af ("tty: pty: Fix race condition between release_one_tty and pty_write")
Reported-by: kernel test robot <lkp@intel.com>
Cc: Sahara <keun-o.park@darkmatter.ae>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/pty.c    | 7 -------
 drivers/tty/tty_io.c | 3 ---
 2 files changed, 10 deletions(-)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index ef72031ab5b9..00099a8439d2 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -116,12 +116,6 @@ static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c)
 	if (tty->stopped)
 		return 0;
 
-	mutex_lock(&tty_mutex);
-	if (to->magic != TTY_MAGIC) {
-		mutex_unlock(&tty_mutex);
-		return -EIO;
-	}
-
 	if (c > 0) {
 		spin_lock_irqsave(&to->port->lock, flags);
 		/* Stuff the data into the input queue of the other end */
@@ -131,7 +125,6 @@ static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c)
 			tty_flip_buffer_push(to->port);
 		spin_unlock_irqrestore(&to->port->lock, flags);
 	}
-	mutex_unlock(&tty_mutex);
 	return c;
 }
 
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index c27777f3b8c4..5fa250157025 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1448,13 +1448,10 @@ static void release_one_tty(struct work_struct *work)
 	struct tty_driver *driver = tty->driver;
 	struct module *owner = driver->owner;
 
-	mutex_lock(&tty_mutex);
 	if (tty->ops->cleanup)
 		tty->ops->cleanup(tty);
 
 	tty->magic = 0;
-	mutex_unlock(&tty_mutex);
-
 	tty_driver_kref_put(driver);
 	module_put(owner);
 
-- 
2.21.0