From: Alan Cox Date: Tue, 29 May 2012 12:45:01 +0000 (+0100) Subject: pty: Fix lock inversion X-Git-Tag: firefly_0821_release~3680^2~2732 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=d3ca8b64b97e;p=firefly-linux-kernel-4.4.55.git 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 Acked-by: Greg Kroah-Hartman Signed-off-by: Linus Torvalds --- 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 */