[PATCH] pty: Fix lock inversion

Alan Cox
2012-05-24T14:35:47Z

From: Alan Cox <alan@linux.intel.com>

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>
---

drivers/tty/pty.c | 2 --
1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 59af394..65c7c62 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 */