From d3ca8b64b97ef4dc54d7bb0b88bbc01a1fca8cb9 Mon Sep 17 00:00:00 2001
From: Alan Cox <alan@linux.intel.com>
Date: Tue, 29 May 2012 13:45:01 +0100
Subject: pty: Fix lock inversion
The ptmx_open path takes the tty and devpts locks in the wrong order
because tty_init_dev locks and returns a locked tty. As far as I can
tell this is actually safe anyway because the tty being returned is new
so nobody can get a reference to lock it at this point.
However we don't even need the devpts lock at this point, it's only held
as a byproduct of the way the locks were pushe down.
Signed-off-by: Alan Cox <alan@linux.intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
drivers/tty/pty.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 59af3945ea85..65c7c62c7aae 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -633,7 +633,6 @@ static int ptmx_open(struct inode *inode, struct file *filp)
mutex_unlock(&devpts_mutex);
mutex_lock(&tty_mutex);
- mutex_lock(&devpts_mutex);
tty = tty_init_dev(ptm_driver, index);
if (IS_ERR(tty)) {
@@ -643,7 +642,6 @@ static int ptmx_open(struct inode *inode, struct file *filp)
/* The tty returned here is locked so we can safely
drop the mutex */
- mutex_unlock(&devpts_mutex);
mutex_unlock(&tty_mutex);
set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */
--
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