tty: Revert the tty locking series, it needs more work

This reverts the tty layer change to use per-tty locking, because it's
not correct yet, and fixing it will require some more deep surgery.

The main revert is d29f3ef39be4 ("tty_lock: Localise the lock"), but
there are several smaller commits that built upon it, they also get
reverted here. The list of reverted commits is:

  fde86d310886 - tty: add lockdep annotations
  8f6576ad476b - tty: fix ldisc lock inversion trace
  d3ca8b64b97e - pty: Fix lock inversion
  b1d679afd766 - tty: drop the pty lock during hangup
  abcefe5fc357 - tty/amiserial: Add missing argument for tty_unlock()
  fd11b42e3598 - cris: fix missing tty arg in wait_event_interruptible_tty call
  d29f3ef39be4 - tty_lock: Localise the lock

The revert had a trivial conflict in the 68360serial.c staging driver
that got removed in the meantime.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

12 files changed, 108 insertions, 175 deletions

diff --git a/drivers/tty/amiserial.c b/drivers/tty/amiserial.c
index 35819e312624..6cc4358f68c1 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);
+        tty_lock();
         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);
+        tty_unlock();
         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);
+        tty_lock();
         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);
+                tty_unlock();
                 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);
+                        tty_unlock();
                         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);
+                tty_unlock();
                 return -EINVAL;
         }
 
@@ -1116,7 +1116,7 @@ check_and_exit:
                 }
         } else
                 retval = startup(tty, state);
-        tty_unlock(tty);
+        tty_unlock();
         return retval;
 }
 
diff --git a/drivers/tty/cyclades.c b/drivers/tty/cyclades.c
index 6984e1a2686a..e61cabdd69df 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(tty, info->port.close_wait,
+                wait_event_interruptible_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 656ad93bbc96..5c6c31459a2f 100644
--- a/drivers/tty/n_r3964.c
+++ b/drivers/tty/n_r3964.c
@@ -1065,8 +1065,7 @@ static ssize_t r3964_read(struct tty_struct *tty, struct file *file,
 
         TRACE_L("read()");
 
-        /* FIXME: should use a private lock */
-        tty_lock(tty);
+        tty_lock();
 
         pClient = findClient(pInfo, task_pid(current));
         if (pClient) {
@@ -1078,7 +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(tty, pInfo->read_wait,
+                        wait_event_interruptible_tty(pInfo->read_wait,
                                         (pMsg = remove_msg(pInfo, pClient)));
                 }
 
@@ -1108,7 +1107,7 @@ static ssize_t r3964_read(struct tty_struct *tty, struct file *file,
         }
         ret = -EPERM;
 unlock:
-        tty_unlock(tty);
+        tty_unlock();
         return ret;
 }
 
@@ -1157,7 +1156,7 @@ static ssize_t r3964_write(struct tty_struct *tty, struct file *file,
         pHeader->locks = 0;
         pHeader->owner = NULL;
 
-        tty_lock(tty);
+        tty_lock();
 
         pClient = findClient(pInfo, task_pid(current));
         if (pClient) {
@@ -1176,7 +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);
+        tty_unlock();
 
         return 0;
 }
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 65c7c62c7aae..5505ffc91da4 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -47,7 +47,6 @@ 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;
@@ -63,9 +62,9 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
                         mutex_unlock(&devpts_mutex);
                 }
 #endif
-                tty_unlock(tty);
+                tty_unlock();
                 tty_vhangup(tty->link);
-                tty_lock(tty);
+                tty_lock();
         }
 }
 
@@ -623,27 +622,26 @@ static int ptmx_open(struct inode *inode, struct file *filp)
                 return retval;
 
         /* find a device that is not in use. */
-        mutex_lock(&devpts_mutex);
+        tty_lock();
         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);
@@ -656,17 +654,16 @@ static int ptmx_open(struct inode *inode, struct file *filp)
         if (retval)
                 goto err_release;
 
-        tty_unlock(tty);
+        tty_unlock();
         return 0;
 err_release:
-        tty_unlock(tty);
+        tty_unlock();
         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 7264d4d26717..80b6b1b1f725 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(tty, info->close_wait,
+                wait_event_interruptible_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);
+                tty_unlock();
                 schedule();
-                tty_lock(tty);
+                tty_lock();
         }
         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(tty, info->close_wait,
+                wait_event_interruptible_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 5ed0daae6564..593d40ad0a6b 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);
+                tty_unlock();
                 schedule();
-                tty_lock(tty);
+                tty_lock();
         }
         
         set_current_state(TASK_RUNNING);
diff --git a/drivers/tty/synclink_gt.c b/drivers/tty/synclink_gt.c
index 45b43f11ca39..aa1debf97cc7 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);
+                tty_unlock();
                 schedule();
-                tty_lock(tty);
+                tty_lock();
         }
 
         set_current_state(TASK_RUNNING);
diff --git a/drivers/tty/synclinkmp.c b/drivers/tty/synclinkmp.c
index 4a1e4f07765b..a3dddc12d2fe 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);
+                tty_unlock();
                 schedule();
-                tty_lock(tty);
+                tty_lock();
         }
 
         set_current_state(TASK_RUNNING);
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 9e930c009bf2..b425c79675ad 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -185,7 +185,6 @@ 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);
 }
 
@@ -574,7 +573,7 @@ void __tty_hangup(struct tty_struct *tty)
         }
         spin_unlock(&redirect_lock);
 
-        tty_lock(tty);
+        tty_lock();
 
         /* some functions below drop BTM, so we need this bit */
         set_bit(TTY_HUPPING, &tty->flags);
@@ -667,7 +666,7 @@ void __tty_hangup(struct tty_struct *tty)
         clear_bit(TTY_HUPPING, &tty->flags);
         tty_ldisc_enable(tty);
 
-        tty_unlock(tty);
+        tty_unlock();
 
         if (f)
                 fput(f);
@@ -1104,12 +1103,12 @@ void tty_write_message(struct tty_struct *tty, char *msg)
 {
         if (tty) {
                 mutex_lock(&tty->atomic_write_lock);
-                tty_lock(tty);
+                tty_lock();
                 if (tty->ops->write && !test_bit(TTY_CLOSING, &tty->flags)) {
-                        tty_unlock(tty);
+                        tty_unlock();
                         tty->ops->write(tty, msg, strlen(msg));
                 } else
-                        tty_unlock(tty);
+                        tty_unlock();
                 tty_write_unlock(tty);
         }
         return;
@@ -1404,7 +1403,6 @@ 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;
@@ -1417,11 +1415,9 @@ 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:
@@ -1430,7 +1426,6 @@ 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);
@@ -1633,7 +1628,7 @@ int tty_release(struct inode *inode, struct file *filp)
         if (tty_paranoia_check(tty, inode, __func__))
                 return 0;
 
-        tty_lock(tty);
+        tty_lock();
         check_tty_count(tty, __func__);
 
         __tty_fasync(-1, filp, 0);
@@ -1642,11 +1637,10 @@ 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);
+                tty_unlock();
                 return 0;
         }
 
@@ -1658,7 +1652,7 @@ int tty_release(struct inode *inode, struct file *filp)
         if (tty->ops->close)
                 tty->ops->close(tty, filp);
 
-        tty_unlock(tty);
+        tty_unlock();
         /*
          * 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
@@ -1681,7 +1675,7 @@ int tty_release(struct inode *inode, struct file *filp)
                    opens on /dev/tty */
 
                 mutex_lock(&tty_mutex);
-                tty_lock_pair(tty, o_tty);
+                tty_lock();
                 tty_closing = tty->count <= 1;
                 o_tty_closing = o_tty &&
                         (o_tty->count <= (pty_master ? 1 : 0));
@@ -1712,7 +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_pair(tty, o_tty);
+                tty_unlock();
                 mutex_unlock(&tty_mutex);
                 schedule();
         }
@@ -1775,7 +1769,7 @@ int tty_release(struct inode *inode, struct file *filp)
 
         /* check whether both sides are closing ... */
         if (!tty_closing || (o_tty && !o_tty_closing)) {
-                tty_unlock_pair(tty, o_tty);
+                tty_unlock();
                 return 0;
         }
 
@@ -1788,16 +1782,14 @@ 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 tty_unlock_pair
-         * should be safe as we keep a kref while the tty is locked (so the
-         * unlock never unlocks a freed tty).
+         * the slots and preserving the termios structure.
          */
         release_tty(tty, idx);
-        tty_unlock_pair(tty, o_tty);
 
         /* Make this pty number available for reallocation */
         if (devpts)
                 devpts_kill_index(inode, idx);
+        tty_unlock();
         return 0;
 }
 
@@ -1901,9 +1893,6 @@ 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)
@@ -1927,7 +1916,8 @@ retry_open:
         retval = 0;
 
         mutex_lock(&tty_mutex);
-        /* This is protected by the tty_mutex */
+        tty_lock();
+
         tty = tty_open_current_tty(device, filp);
         if (IS_ERR(tty)) {
                 retval = PTR_ERR(tty);
@@ -1948,19 +1938,17 @@ retry_open:
         }
 
         if (tty) {
-                tty_lock(tty);
                 retval = tty_reopen(tty);
-                if (retval < 0) {
-                        tty_unlock(tty);
+                if (retval)
                         tty = ERR_PTR(retval);
-                }
-        } else  /* Returns with the tty_lock held for now */
+        } else
                 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;
         }
@@ -1989,7 +1977,7 @@ retry_open:
                 printk(KERN_DEBUG "%s: error %d in opening %s...\n", __func__,
                                 retval, tty->name);
 #endif
-                tty_unlock(tty); /* need to call tty_release without BTM */
+                tty_unlock(); /* need to call tty_release without BTM */
                 tty_release(inode, filp);
                 if (retval != -ERESTARTSYS)
                         return retval;
@@ -2001,15 +1989,17 @@ 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);
+        tty_unlock();
 
 
         mutex_lock(&tty_mutex);
-        tty_lock(tty);
+        tty_lock();
         spin_lock_irq(&current->sighand->siglock);
         if (!noctty &&
             current->signal->leader &&
@@ -2017,10 +2007,11 @@ retry_open:
             tty->session == NULL)
                 __proc_set_tty(current, tty);
         spin_unlock_irq(&current->sighand->siglock);
-        tty_unlock(tty);
+        tty_unlock();
         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))
@@ -2103,13 +2094,10 @@ out:
 
 static int tty_fasync(int fd, struct file *filp, int on)
 {
-        struct tty_struct *tty = file_tty(filp);
         int retval;
-
-        tty_lock(tty);
+        tty_lock();
         retval = __tty_fasync(fd, filp, on);
-        tty_unlock(tty);
-
+        tty_unlock();
         return retval;
 }
 
@@ -2946,7 +2934,6 @@ 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 ba8be396a621..9911eb6b34cd 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);
+        tty_lock();
         /*
          *      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);
+                tty_unlock();
                 tty_ldisc_put(new_ldisc);
                 return 0;
         }
 
-        tty_unlock(tty);
+        tty_unlock();
         /*
          *      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);
+        tty_lock();
         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);
+                tty_unlock();
                 wait_event(tty_ldisc_wait,
                         test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
-                tty_lock(tty);
+                tty_lock();
                 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);
+        tty_unlock();
         /*
          *      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);
+        tty_lock();
         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);
+                tty_unlock();
                 return -EIO;
         }
 
@@ -708,7 +708,7 @@ enable:
         if (o_work)
                 schedule_work(&o_tty->buf.work);
         mutex_unlock(&tty->ldisc_mutex);
-        tty_unlock(tty);
+        tty_unlock();
         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);
+        tty_unlock();
         cancel_work_sync(&tty->buf.work);
         mutex_unlock(&tty->ldisc_mutex);
 retry:
-        tty_lock(tty);
+        tty_lock();
         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);
+                        tty_unlock();
 
                         while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) {
                                 timeout = MAX_SCHEDULE_TIMEOUT;
@@ -894,23 +894,6 @@ 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
@@ -929,19 +912,27 @@ void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
          * race with the set_ldisc code path.
          */
 
-        tty_unlock_pair(tty, o_tty);
+        tty_unlock();
         tty_ldisc_halt(tty);
         tty_ldisc_flush_works(tty);
-        if (o_tty) {
-                tty_ldisc_halt(o_tty);
-                tty_ldisc_flush_works(o_tty);
-        }
-        tty_lock_pair(tty, o_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_ldisc_kill(tty);
+        /* This will need doing differently if we need to lock */
         if (o_tty)
-                tty_ldisc_kill(o_tty);
+                tty_ldisc_release(o_tty, NULL);
 
         /* 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 67feac9e6ebb..9ff986c32a21 100644
--- a/drivers/tty/tty_mutex.c
+++ b/drivers/tty/tty_mutex.c
@@ -4,70 +4,29 @@
 #include <linux/semaphore.h>
 #include <linux/sched.h>
 
-/* Legacy tty mutex glue */
-
-enum {
-        TTY_MUTEX_NORMAL,
-        TTY_MUTEX_NESTED,
-};
+/*
+ * 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);
 
 /*
  * Getting the big tty mutex.
  */
-
-static void __lockfunc tty_lock_nested(struct tty_struct *tty,
-                                       unsigned int subclass)
+void __lockfunc tty_lock(void)
 {
-        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);
+        mutex_lock(&big_tty_mutex);
 }
 EXPORT_SYMBOL(tty_lock);
 
-void __lockfunc tty_unlock(struct tty_struct *tty)
+void __lockfunc tty_unlock(void)
 {
-        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);
+        mutex_unlock(&big_tty_mutex);
 }
 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 d9cca95a5452..bf6e238146ae 100644
--- a/drivers/tty/tty_port.c
+++ b/drivers/tty/tty_port.c
@@ -230,7 +230,7 @@ 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(tty, port->close_wait,
+                wait_event_interruptible_tty(port->close_wait,
                                 !(port->flags & ASYNC_CLOSING));
                 if (port->flags & ASYNC_HUP_NOTIFY)
                         return -EAGAIN;
@@ -296,9 +296,9 @@ int tty_port_block_til_ready(struct tty_port *port,
                         retval = -ERESTARTSYS;
                         break;
                 }
-                tty_unlock(tty);
+                tty_unlock();
                 schedule();
-                tty_lock(tty);
+                tty_lock();
         }
         finish_wait(&port->open_wait, &wait);