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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>
This commit is contained in:
Alan Cox 2012-05-29 13:45:01 +01:00 committed by Linus Torvalds
parent a01ee165a1
commit d3ca8b64b9
1 changed files with 0 additions and 2 deletions
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2
drivers/tty/pty.c
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@ -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 */