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Commit d3ca8b64 authored by Alan Cox's avatar Alan Cox Committed by Linus Torvalds
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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: default avatarAlan Cox <alan@linux.intel.com>
Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a01ee165

drivers/tty/pty.c

+0 −2
Original line number Diff line number Diff line
@@ -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 */