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pty: Fix lock inversion

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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 <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Alan Cox authored and Linus Torvalds committed 2012-05-29 10:42:13 -07:00
1 parent a01ee165a1
commit d3ca8b64b9
1 file changed
-2
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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 */