tty: localise the lock

The termios and other changes mean the other protections needed on the driver
tty arrays should be adequate. Turn it all back on.

This contains pieces folded in from the fixes made to the original patches

| From: Geert Uytterhoeven <geert@linux-m68k.org>	(fix m68k)
| From: Paul Gortmaker <paul.gortmaker@windriver.com>	(fix cris)
| From: Jiri Kosina <jkosina@suze.cz>			(lockdep)
| From: Eric Dumazet <eric.dumazet@gmail.com>		(lockdep)

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

12 files changed, 174 insertions, 109 deletions

diff --git a/drivers/tty/amiserial.c b/drivers/tty/amiserial.c
index 0e8441e..998731f 100644
--- a/drivers/tty/amiserial.c
+++ b/drivers/tty/amiserial.c
@@ -1033,7 +1033,7 @@ static int get_serial_info(struct tty_struct *tty, struct serial_state *state,
 	if (!retinfo)
 		return -EFAULT;
 	memset(&tmp, 0, sizeof(tmp));
-	tty_lock();
+	tty_lock(tty);
 	tmp.line = tty->index;
 	tmp.port = state->port;
 	tmp.flags = state->tport.flags;
@@ -1042,7 +1042,7 @@ static int get_serial_info(struct tty_struct *tty, struct serial_state *state,
 	tmp.close_delay = state->tport.close_delay;
 	tmp.closing_wait = state->tport.closing_wait;
 	tmp.custom_divisor = state->custom_divisor;
-	tty_unlock();
+	tty_unlock(tty);
 	if (copy_to_user(retinfo,&tmp,sizeof(*retinfo)))
 		return -EFAULT;
 	return 0;
@@ -1059,12 +1059,12 @@ static int set_serial_info(struct tty_struct *tty, struct serial_state *state,
 	if (copy_from_user(&new_serial,new_info,sizeof(new_serial)))
 		return -EFAULT;
 
-	tty_lock();
+	tty_lock(tty);
 	change_spd = ((new_serial.flags ^ port->flags) & ASYNC_SPD_MASK) ||
 		new_serial.custom_divisor != state->custom_divisor;
 	if (new_serial.irq || new_serial.port != state->port ||
 			new_serial.xmit_fifo_size != state->xmit_fifo_size) {
-		tty_unlock();
+		tty_unlock(tty);
 		return -EINVAL;
 	}
   
@@ -1074,7 +1074,7 @@ static int set_serial_info(struct tty_struct *tty, struct serial_state *state,
 		    (new_serial.xmit_fifo_size != state->xmit_fifo_size) ||
 		    ((new_serial.flags & ~ASYNC_USR_MASK) !=
 		     (port->flags & ~ASYNC_USR_MASK))) {
-			tty_unlock();
+			tty_unlock(tty);
 			return -EPERM;
 		}
 		port->flags = ((port->flags & ~ASYNC_USR_MASK) |
@@ -1084,7 +1084,7 @@ static int set_serial_info(struct tty_struct *tty, struct serial_state *state,
 	}
 
 	if (new_serial.baud_base < 9600) {
-		tty_unlock();
+		tty_unlock(tty);
 		return -EINVAL;
 	}
 
@@ -1116,7 +1116,7 @@ check_and_exit:
 		}
 	} else
 		retval = startup(tty, state);
-	tty_unlock();
+	tty_unlock(tty);
 	return retval;
 }
 
diff --git a/drivers/tty/cyclades.c b/drivers/tty/cyclades.c
index e77db71..c8850ea 100644
--- a/drivers/tty/cyclades.c
+++ b/drivers/tty/cyclades.c
@@ -1599,7 +1599,7 @@ static int cy_open(struct tty_struct *tty, struct file *filp)
 	 * If the port is the middle of closing, bail out now
 	 */
 	if (tty_hung_up_p(filp) || (info->port.flags & ASYNC_CLOSING)) {
-		wait_event_interruptible_tty(info->port.close_wait,
+		wait_event_interruptible_tty(tty, info->port.close_wait,
 				!(info->port.flags & ASYNC_CLOSING));
 		return (info->port.flags & ASYNC_HUP_NOTIFY) ? -EAGAIN: -ERESTARTSYS;
 	}
diff --git a/drivers/tty/n_r3964.c b/drivers/tty/n_r3964.c
index 5c6c314..1e64050 100644
--- a/drivers/tty/n_r3964.c
+++ b/drivers/tty/n_r3964.c
@@ -1065,7 +1065,7 @@ static ssize_t r3964_read(struct tty_struct *tty, struct file *file,
 
 	TRACE_L("read()");
 
-	tty_lock();
+	tty_lock(tty);
 
 	pClient = findClient(pInfo, task_pid(current));
 	if (pClient) {
@@ -1077,7 +1077,7 @@ static ssize_t r3964_read(struct tty_struct *tty, struct file *file,
 				goto unlock;
 			}
 			/* block until there is a message: */
-			wait_event_interruptible_tty(pInfo->read_wait,
+			wait_event_interruptible_tty(tty, pInfo->read_wait,
 					(pMsg = remove_msg(pInfo, pClient)));
 		}
 
@@ -1107,7 +1107,7 @@ static ssize_t r3964_read(struct tty_struct *tty, struct file *file,
 	}
 	ret = -EPERM;
 unlock:
-	tty_unlock();
+	tty_unlock(tty);
 	return ret;
 }
 
@@ -1156,7 +1156,7 @@ static ssize_t r3964_write(struct tty_struct *tty, struct file *file,
 	pHeader->locks = 0;
 	pHeader->owner = NULL;
 
-	tty_lock();
+	tty_lock(tty);
 
 	pClient = findClient(pInfo, task_pid(current));
 	if (pClient) {
@@ -1175,7 +1175,7 @@ static ssize_t r3964_write(struct tty_struct *tty, struct file *file,
 	add_tx_queue(pInfo, pHeader);
 	trigger_transmit(pInfo);
 
-	tty_unlock();
+	tty_unlock(tty);
 
 	return 0;
 }
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index d6579a9..4399f1d 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -47,6 +47,7 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
 	wake_up_interruptible(&tty->read_wait);
 	wake_up_interruptible(&tty->write_wait);
 	tty->packet = 0;
+	/* Review - krefs on tty_link ?? */
 	if (!tty->link)
 		return;
 	tty->link->packet = 0;
@@ -62,9 +63,9 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
 		        mutex_unlock(&devpts_mutex);
 		}
 #endif
-		tty_unlock();
+		tty_unlock(tty);
 		tty_vhangup(tty->link);
-		tty_lock();
+		tty_lock(tty);
 	}
 }
 
@@ -617,26 +618,27 @@ static int ptmx_open(struct inode *inode, struct file *filp)
 		return retval;
 
 	/* find a device that is not in use. */
-	tty_lock();
+	mutex_lock(&devpts_mutex);
 	index = devpts_new_index(inode);
-	tty_unlock();
 	if (index < 0) {
 		retval = index;
 		goto err_file;
 	}
 
+	mutex_unlock(&devpts_mutex);
+
 	mutex_lock(&tty_mutex);
-	mutex_lock(&devpts_mutex);
 	tty = tty_init_dev(ptm_driver, index);
-	mutex_unlock(&devpts_mutex);
-	tty_lock();
-	mutex_unlock(&tty_mutex);
 
 	if (IS_ERR(tty)) {
 		retval = PTR_ERR(tty);
 		goto out;
 	}
 
+	/* The tty returned here is locked so we can safely
+	   drop the mutex */
+	mutex_unlock(&tty_mutex);
+
 	set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */
 
 	tty_add_file(tty, filp);
@@ -649,16 +651,17 @@ static int ptmx_open(struct inode *inode, struct file *filp)
 	if (retval)
 		goto err_release;
 
-	tty_unlock();
+	tty_unlock(tty);
 	return 0;
 err_release:
-	tty_unlock();
+	tty_unlock(tty);
 	tty_release(inode, filp);
 	return retval;
 out:
+	mutex_unlock(&tty_mutex);
 	devpts_kill_index(inode, index);
-	tty_unlock();
 err_file:
+        mutex_unlock(&devpts_mutex);
 	tty_free_file(filp);
 	return retval;
 }
diff --git a/drivers/tty/serial/crisv10.c b/drivers/tty/serial/crisv10.c
index 6b705b2..a770b10 100644
--- a/drivers/tty/serial/crisv10.c
+++ b/drivers/tty/serial/crisv10.c
@@ -3976,7 +3976,7 @@ block_til_ready(struct tty_struct *tty, struct file * filp,
 	 */
 	if (tty_hung_up_p(filp) ||
 	    (info->flags & ASYNC_CLOSING)) {
-		wait_event_interruptible_tty(info->close_wait,
+		wait_event_interruptible_tty(tty, info->close_wait,
 			!(info->flags & ASYNC_CLOSING));
 #ifdef SERIAL_DO_RESTART
 		if (info->flags & ASYNC_HUP_NOTIFY)
@@ -4052,9 +4052,9 @@ block_til_ready(struct tty_struct *tty, struct file * filp,
 		printk("block_til_ready blocking: ttyS%d, count = %d\n",
 		       info->line, info->count);
 #endif
-		tty_unlock();
+		tty_unlock(tty);
 		schedule();
-		tty_lock();
+		tty_lock(tty);
 	}
 	set_current_state(TASK_RUNNING);
 	remove_wait_queue(&info->open_wait, &wait);
@@ -4115,7 +4115,7 @@ rs_open(struct tty_struct *tty, struct file * filp)
 	 */
 	if (tty_hung_up_p(filp) ||
 	    (info->flags & ASYNC_CLOSING)) {
-		wait_event_interruptible_tty(info->close_wait,
+		wait_event_interruptible_tty(tty, info->close_wait,
 			!(info->flags & ASYNC_CLOSING));
 #ifdef SERIAL_DO_RESTART
 		return ((info->flags & ASYNC_HUP_NOTIFY) ?
diff --git a/drivers/tty/synclink.c b/drivers/tty/synclink.c
index bdeeb31..991bae8 100644
--- a/drivers/tty/synclink.c
+++ b/drivers/tty/synclink.c
@@ -3338,9 +3338,9 @@ static int block_til_ready(struct tty_struct *tty, struct file * filp,
 			printk("%s(%d):block_til_ready blocking on %s count=%d\n",
 				 __FILE__,__LINE__, tty->driver->name, port->count );
 				 
-		tty_unlock();
+		tty_unlock(tty);
 		schedule();
-		tty_lock();
+		tty_lock(tty);
 	}
 	
 	set_current_state(TASK_RUNNING);
diff --git a/drivers/tty/synclink_gt.c b/drivers/tty/synclink_gt.c
index f02d18a..9130253 100644
--- a/drivers/tty/synclink_gt.c
+++ b/drivers/tty/synclink_gt.c
@@ -3336,9 +3336,9 @@ static int block_til_ready(struct tty_struct *tty, struct file *filp,
 		}
 
 		DBGINFO(("%s block_til_ready wait\n", tty->driver->name));
-		tty_unlock();
+		tty_unlock(tty);
 		schedule();
-		tty_lock();
+		tty_lock(tty);
 	}
 
 	set_current_state(TASK_RUNNING);
diff --git a/drivers/tty/synclinkmp.c b/drivers/tty/synclinkmp.c
index ae75a3c..95fd4e2 100644
--- a/drivers/tty/synclinkmp.c
+++ b/drivers/tty/synclinkmp.c
@@ -3357,9 +3357,9 @@ static int block_til_ready(struct tty_struct *tty, struct file *filp,
 			printk("%s(%d):%s block_til_ready() count=%d\n",
 				 __FILE__,__LINE__, tty->driver->name, port->count );
 
-		tty_unlock();
+		tty_unlock(tty);
 		schedule();
-		tty_lock();
+		tty_lock(tty);
 	}
 
 	set_current_state(TASK_RUNNING);
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 6784aae..6902244 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -187,6 +187,7 @@ void free_tty_struct(struct tty_struct *tty)
 		put_device(tty->dev);
 	kfree(tty->write_buf);
 	tty_buffer_free_all(tty);
+	tty->magic = 0xDEADDEAD;
 	kfree(tty);
 }
 
@@ -575,7 +576,7 @@ void __tty_hangup(struct tty_struct *tty)
 	}
 	spin_unlock(&redirect_lock);
 
-	tty_lock();
+	tty_lock(tty);
 
 	/* some functions below drop BTM, so we need this bit */
 	set_bit(TTY_HUPPING, &tty->flags);
@@ -668,7 +669,7 @@ void __tty_hangup(struct tty_struct *tty)
 	clear_bit(TTY_HUPPING, &tty->flags);
 	tty_ldisc_enable(tty);
 
-	tty_unlock();
+	tty_unlock(tty);
 
 	if (f)
 		fput(f);
@@ -1105,12 +1106,12 @@ void tty_write_message(struct tty_struct *tty, char *msg)
 {
 	if (tty) {
 		mutex_lock(&tty->atomic_write_lock);
-		tty_lock();
+		tty_lock(tty);
 		if (tty->ops->write && !test_bit(TTY_CLOSING, &tty->flags)) {
-			tty_unlock();
+			tty_unlock(tty);
 			tty->ops->write(tty, msg, strlen(msg));
 		} else
-			tty_unlock();
+			tty_unlock(tty);
 		tty_write_unlock(tty);
 	}
 	return;
@@ -1403,6 +1404,7 @@ struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx)
 	}
 	initialize_tty_struct(tty, driver, idx);
 
+	tty_lock(tty);
 	retval = tty_driver_install_tty(driver, tty);
 	if (retval < 0)
 		goto err_deinit_tty;
@@ -1418,9 +1420,11 @@ struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx)
 	retval = tty_ldisc_setup(tty, tty->link);
 	if (retval)
 		goto err_release_tty;
+	/* Return the tty locked so that it cannot vanish under the caller */
 	return tty;
 
 err_deinit_tty:
+	tty_unlock(tty);
 	deinitialize_tty_struct(tty);
 	free_tty_struct(tty);
 err_module_put:
@@ -1429,6 +1433,7 @@ err_module_put:
 
 	/* call the tty release_tty routine to clean out this slot */
 err_release_tty:
+	tty_unlock(tty);
 	printk_ratelimited(KERN_INFO "tty_init_dev: ldisc open failed, "
 				 "clearing slot %d\n", idx);
 	release_tty(tty, idx);
@@ -1622,7 +1627,7 @@ int tty_release(struct inode *inode, struct file *filp)
 	if (tty_paranoia_check(tty, inode, __func__))
 		return 0;
 
-	tty_lock();
+	tty_lock(tty);
 	check_tty_count(tty, __func__);
 
 	__tty_fasync(-1, filp, 0);
@@ -1631,10 +1636,11 @@ int tty_release(struct inode *inode, struct file *filp)
 	pty_master = (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
 		      tty->driver->subtype == PTY_TYPE_MASTER);
 	devpts = (tty->driver->flags & TTY_DRIVER_DEVPTS_MEM) != 0;
+	/* Review: parallel close */
 	o_tty = tty->link;
 
 	if (tty_release_checks(tty, o_tty, idx)) {
-		tty_unlock();
+		tty_unlock(tty);
 		return 0;
 	}
 
@@ -1646,7 +1652,7 @@ int tty_release(struct inode *inode, struct file *filp)
 	if (tty->ops->close)
 		tty->ops->close(tty, filp);
 
-	tty_unlock();
+	tty_unlock(tty);
 	/*
 	 * Sanity check: if tty->count is going to zero, there shouldn't be
 	 * any waiters on tty->read_wait or tty->write_wait.  We test the
@@ -1669,7 +1675,7 @@ int tty_release(struct inode *inode, struct file *filp)
 		   opens on /dev/tty */
 
 		mutex_lock(&tty_mutex);
-		tty_lock();
+		tty_lock_pair(tty, o_tty);
 		tty_closing = tty->count <= 1;
 		o_tty_closing = o_tty &&
 			(o_tty->count <= (pty_master ? 1 : 0));
@@ -1700,7 +1706,7 @@ int tty_release(struct inode *inode, struct file *filp)
 
 		printk(KERN_WARNING "%s: %s: read/write wait queue active!\n",
 				__func__, tty_name(tty, buf));
-		tty_unlock();
+		tty_unlock_pair(tty, o_tty);
 		mutex_unlock(&tty_mutex);
 		schedule();
 	}
@@ -1763,7 +1769,7 @@ int tty_release(struct inode *inode, struct file *filp)
 	}
 
 	mutex_unlock(&tty_mutex);
-	tty_unlock();
+	tty_unlock_pair(tty, o_tty);
 	/* At this point the TTY_CLOSING flag should ensure a dead tty
 	   cannot be re-opened by a racing opener */
 
@@ -1780,7 +1786,9 @@ int tty_release(struct inode *inode, struct file *filp)
 	tty_ldisc_release(tty, o_tty);
 	/*
 	 * The release_tty function takes care of the details of clearing
-	 * the slots and preserving the termios structure.
+	 * the slots and preserving the termios structure. The tty_unlock_pair
+	 * should be safe as we keep a kref while the tty is locked (so the
+	 * unlock never unlocks a freed tty).
 	 */
 	mutex_lock(&tty_mutex);
 	release_tty(tty, idx);
@@ -1789,7 +1797,6 @@ int tty_release(struct inode *inode, struct file *filp)
 	/* Make this pty number available for reallocation */
 	if (devpts)
 		devpts_kill_index(inode, idx);
-
 	return 0;
 }
 
@@ -1893,6 +1900,9 @@ static struct tty_driver *tty_lookup_driver(dev_t device, struct file *filp,
  *	Locking: tty_mutex protects tty, tty_lookup_driver and tty_init_dev.
  *		 tty->count should protect the rest.
  *		 ->siglock protects ->signal/->sighand
+ *
+ *	Note: the tty_unlock/lock cases without a ref are only safe due to
+ *	tty_mutex
  */
 
 static int tty_open(struct inode *inode, struct file *filp)
@@ -1916,8 +1926,7 @@ retry_open:
 	retval = 0;
 
 	mutex_lock(&tty_mutex);
-	tty_lock();
-
+	/* This is protected by the tty_mutex */
 	tty = tty_open_current_tty(device, filp);
 	if (IS_ERR(tty)) {
 		retval = PTR_ERR(tty);
@@ -1938,17 +1947,19 @@ retry_open:
 	}
 
 	if (tty) {
+		tty_lock(tty);
 		retval = tty_reopen(tty);
-		if (retval)
+		if (retval < 0) {
+			tty_unlock(tty);
 			tty = ERR_PTR(retval);
-	} else
+		}
+	} else	/* Returns with the tty_lock held for now */
 		tty = tty_init_dev(driver, index);
 
 	mutex_unlock(&tty_mutex);
 	if (driver)
 		tty_driver_kref_put(driver);
 	if (IS_ERR(tty)) {
-		tty_unlock();
 		retval = PTR_ERR(tty);
 		goto err_file;
 	}
@@ -1977,7 +1988,7 @@ retry_open:
 		printk(KERN_DEBUG "%s: error %d in opening %s...\n", __func__,
 				retval, tty->name);
 #endif
-		tty_unlock(); /* need to call tty_release without BTM */
+		tty_unlock(tty); /* need to call tty_release without BTM */
 		tty_release(inode, filp);
 		if (retval != -ERESTARTSYS)
 			return retval;
@@ -1989,17 +2000,15 @@ retry_open:
 		/*
 		 * Need to reset f_op in case a hangup happened.
 		 */
-		tty_lock();
 		if (filp->f_op == &hung_up_tty_fops)
 			filp->f_op = &tty_fops;
-		tty_unlock();
 		goto retry_open;
 	}
-	tty_unlock();
+	tty_unlock(tty);
 
 
 	mutex_lock(&tty_mutex);
-	tty_lock();
+	tty_lock(tty);
 	spin_lock_irq(&current->sighand->siglock);
 	if (!noctty &&
 	    current->signal->leader &&
@@ -2007,11 +2016,10 @@ retry_open:
 	    tty->session == NULL)
 		__proc_set_tty(current, tty);
 	spin_unlock_irq(&current->sighand->siglock);
-	tty_unlock();
+	tty_unlock(tty);
 	mutex_unlock(&tty_mutex);
 	return 0;
 err_unlock:
-	tty_unlock();
 	mutex_unlock(&tty_mutex);
 	/* after locks to avoid deadlock */
 	if (!IS_ERR_OR_NULL(driver))
@@ -2094,10 +2102,13 @@ out:
 
 static int tty_fasync(int fd, struct file *filp, int on)
 {
+	struct tty_struct *tty = file_tty(filp);
 	int retval;
-	tty_lock();
+
+	tty_lock(tty);
 	retval = __tty_fasync(fd, filp, on);
-	tty_unlock();
+	tty_unlock(tty);
+
 	return retval;
 }
 
@@ -2934,6 +2945,7 @@ void initialize_tty_struct(struct tty_struct *tty,
 	tty->pgrp = NULL;
 	tty->overrun_time = jiffies;
 	tty_buffer_init(tty);
+	mutex_init(&tty->legacy_mutex);
 	mutex_init(&tty->termios_mutex);
 	mutex_init(&tty->ldisc_mutex);
 	init_waitqueue_head(&tty->write_wait);
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 3d06871..4d7b562 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -568,7 +568,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 	if (IS_ERR(new_ldisc))
 		return PTR_ERR(new_ldisc);
 
-	tty_lock();
+	tty_lock(tty);
 	/*
 	 *	We need to look at the tty locking here for pty/tty pairs
 	 *	when both sides try to change in parallel.
@@ -582,12 +582,12 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 	 */
 
 	if (tty->ldisc->ops->num == ldisc) {
-		tty_unlock();
+		tty_unlock(tty);
 		tty_ldisc_put(new_ldisc);
 		return 0;
 	}
 
-	tty_unlock();
+	tty_unlock(tty);
 	/*
 	 *	Problem: What do we do if this blocks ?
 	 *	We could deadlock here
@@ -595,7 +595,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
 	tty_wait_until_sent(tty, 0);
 
-	tty_lock();
+	tty_lock(tty);
 	mutex_lock(&tty->ldisc_mutex);
 
 	/*
@@ -605,10 +605,10 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
 	while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
 		mutex_unlock(&tty->ldisc_mutex);
-		tty_unlock();
+		tty_unlock(tty);
 		wait_event(tty_ldisc_wait,
 			test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
-		tty_lock();
+		tty_lock(tty);
 		mutex_lock(&tty->ldisc_mutex);
 	}
 
@@ -623,7 +623,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
 	o_ldisc = tty->ldisc;
 
-	tty_unlock();
+	tty_unlock(tty);
 	/*
 	 *	Make sure we don't change while someone holds a
 	 *	reference to the line discipline. The TTY_LDISC bit
@@ -650,7 +650,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
 	retval = tty_ldisc_wait_idle(tty, 5 * HZ);
 
-	tty_lock();
+	tty_lock(tty);
 	mutex_lock(&tty->ldisc_mutex);
 
 	/* handle wait idle failure locked */
@@ -665,7 +665,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 		clear_bit(TTY_LDISC_CHANGING, &tty->flags);
 		mutex_unlock(&tty->ldisc_mutex);
 		tty_ldisc_put(new_ldisc);
-		tty_unlock();
+		tty_unlock(tty);
 		return -EIO;
 	}
 
@@ -708,7 +708,7 @@ enable:
 	if (o_work)
 		schedule_work(&o_tty->buf.work);
 	mutex_unlock(&tty->ldisc_mutex);
-	tty_unlock();
+	tty_unlock(tty);
 	return retval;
 }
 
@@ -816,11 +816,11 @@ void tty_ldisc_hangup(struct tty_struct *tty)
 	 * need to wait for another function taking the BTM
 	 */
 	clear_bit(TTY_LDISC, &tty->flags);
-	tty_unlock();
+	tty_unlock(tty);
 	cancel_work_sync(&tty->buf.work);
 	mutex_unlock(&tty->ldisc_mutex);
 retry:
-	tty_lock();
+	tty_lock(tty);
 	mutex_lock(&tty->ldisc_mutex);
 
 	/* At this point we have a closed ldisc and we want to
@@ -831,7 +831,7 @@ retry:
 		if (atomic_read(&tty->ldisc->users) != 1) {
 			char cur_n[TASK_COMM_LEN], tty_n[64];
 			long timeout = 3 * HZ;
-			tty_unlock();
+			tty_unlock(tty);
 
 			while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) {
 				timeout = MAX_SCHEDULE_TIMEOUT;
@@ -894,6 +894,23 @@ int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
 	tty_ldisc_enable(tty);
 	return 0;
 }
+
+static void tty_ldisc_kill(struct tty_struct *tty)
+{
+	mutex_lock(&tty->ldisc_mutex);
+	/*
+	 * Now kill off the ldisc
+	 */
+	tty_ldisc_close(tty, tty->ldisc);
+	tty_ldisc_put(tty->ldisc);
+	/* Force an oops if we mess this up */
+	tty->ldisc = NULL;
+
+	/* Ensure the next open requests the N_TTY ldisc */
+	tty_set_termios_ldisc(tty, N_TTY);
+	mutex_unlock(&tty->ldisc_mutex);
+}
+
 /**
  *	tty_ldisc_release		-	release line discipline
  *	@tty: tty being shut down
@@ -912,29 +929,21 @@ void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
 	 * race with the set_ldisc code path.
 	 */
 
+	tty_lock_pair(tty, o_tty);
 	tty_ldisc_halt(tty);
 	tty_ldisc_flush_works(tty);
-	tty_lock();
-
-	mutex_lock(&tty->ldisc_mutex);
-	/*
-	 * Now kill off the ldisc
-	 */
-	tty_ldisc_close(tty, tty->ldisc);
-	tty_ldisc_put(tty->ldisc);
-	/* Force an oops if we mess this up */
-	tty->ldisc = NULL;
-
-	/* Ensure the next open requests the N_TTY ldisc */
-	tty_set_termios_ldisc(tty, N_TTY);
-	mutex_unlock(&tty->ldisc_mutex);
-
-	tty_unlock();
+	if (o_tty) {
+		tty_ldisc_halt(o_tty);
+		tty_ldisc_flush_works(o_tty);
+	}
 
 	/* This will need doing differently if we need to lock */
+	tty_ldisc_kill(tty);
+
 	if (o_tty)
-		tty_ldisc_release(o_tty, NULL);
+		tty_ldisc_kill(o_tty);
 
+	tty_unlock_pair(tty, o_tty);
 	/* And the memory resources remaining (buffers, termios) will be
 	   disposed of when the kref hits zero */
 }
diff --git a/drivers/tty/tty_mutex.c b/drivers/tty/tty_mutex.c
index 9ff986c..67feac9 100644
--- a/drivers/tty/tty_mutex.c
+++ b/drivers/tty/tty_mutex.c
@@ -4,29 +4,70 @@
 #include <linux/semaphore.h>
 #include <linux/sched.h>
 
-/*
- * The 'big tty mutex'
- *
- * This mutex is taken and released by tty_lock() and tty_unlock(),
- * replacing the older big kernel lock.
- * It can no longer be taken recursively, and does not get
- * released implicitly while sleeping.
- *
- * Don't use in new code.
- */
-static DEFINE_MUTEX(big_tty_mutex);
+/* Legacy tty mutex glue */
+
+enum {
+	TTY_MUTEX_NORMAL,
+	TTY_MUTEX_NESTED,
+};
 
 /*
  * Getting the big tty mutex.
  */
-void __lockfunc tty_lock(void)
+
+static void __lockfunc tty_lock_nested(struct tty_struct *tty,
+				       unsigned int subclass)
 {
-	mutex_lock(&big_tty_mutex);
+	if (tty->magic != TTY_MAGIC) {
+		printk(KERN_ERR "L Bad %p\n", tty);
+		WARN_ON(1);
+		return;
+	}
+	tty_kref_get(tty);
+	mutex_lock_nested(&tty->legacy_mutex, subclass);
+}
+
+void __lockfunc tty_lock(struct tty_struct *tty)
+{
+	return tty_lock_nested(tty, TTY_MUTEX_NORMAL);
 }
 EXPORT_SYMBOL(tty_lock);
 
-void __lockfunc tty_unlock(void)
+void __lockfunc tty_unlock(struct tty_struct *tty)
 {
-	mutex_unlock(&big_tty_mutex);
+	if (tty->magic != TTY_MAGIC) {
+		printk(KERN_ERR "U Bad %p\n", tty);
+		WARN_ON(1);
+		return;
+	}
+	mutex_unlock(&tty->legacy_mutex);
+	tty_kref_put(tty);
 }
 EXPORT_SYMBOL(tty_unlock);
+
+/*
+ * Getting the big tty mutex for a pair of ttys with lock ordering
+ * On a non pty/tty pair tty2 can be NULL which is just fine.
+ */
+void __lockfunc tty_lock_pair(struct tty_struct *tty,
+					struct tty_struct *tty2)
+{
+	if (tty < tty2) {
+		tty_lock(tty);
+		tty_lock_nested(tty2, TTY_MUTEX_NESTED);
+	} else {
+		if (tty2 && tty2 != tty)
+			tty_lock(tty2);
+		tty_lock_nested(tty, TTY_MUTEX_NESTED);
+	}
+}
+EXPORT_SYMBOL(tty_lock_pair);
+
+void __lockfunc tty_unlock_pair(struct tty_struct *tty,
+						struct tty_struct *tty2)
+{
+	tty_unlock(tty);
+	if (tty2 && tty2 != tty)
+		tty_unlock(tty2);
+}
+EXPORT_SYMBOL(tty_unlock_pair);
diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
index edcb827..5246763 100644
--- a/drivers/tty/tty_port.c
+++ b/drivers/tty/tty_port.c
@@ -239,7 +239,7 @@ int tty_port_block_til_ready(struct tty_port *port,
 
 	/* block if port is in the process of being closed */
 	if (tty_hung_up_p(filp) || port->flags & ASYNC_CLOSING) {
-		wait_event_interruptible_tty(port->close_wait,
+		wait_event_interruptible_tty(tty, port->close_wait,
 				!(port->flags & ASYNC_CLOSING));
 		if (port->flags & ASYNC_HUP_NOTIFY)
 			return -EAGAIN;
@@ -305,9 +305,9 @@ int tty_port_block_til_ready(struct tty_port *port,
 			retval = -ERESTARTSYS;
 			break;
 		}
-		tty_unlock();
+		tty_unlock(tty);
 		schedule();
-		tty_lock();
+		tty_lock(tty);
 	}
 	finish_wait(&port->open_wait, &wait);