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 d29f3ef3 ("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:

  fde86d31 - tty: add lockdep annotations
  8f6576ad - tty: fix ldisc lock inversion trace
  d3ca8b64 - pty: Fix lock inversion
  b1d679af - tty: drop the pty lock during hangup
  abcefe5f - tty/amiserial: Add missing argument for tty_unlock()
  fd11b42e - cris: fix missing tty arg in wait_event_interruptible_tty call
  d29f3ef3 - 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>

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 @@ static int set_serial_info(struct tty_struct *tty, struct serial_state *state,
 		}
 	} else
 		retval = startup(tty, state);
-	tty_unlock(tty);
+	tty_unlock();
 	return retval;
 }
 

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;
 	}

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;
 }

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;
 }

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) ?

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);

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);

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);

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 @@ struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx)
 
 	/* 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 @@ static int tty_open(struct inode *inode, struct file *filp)
 	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 @@ static int tty_open(struct inode *inode, struct file *filp)
 	}
 
 	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 @@ static int tty_open(struct inode *inode, struct file *filp)
 		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 @@ static int tty_open(struct inode *inode, struct file *filp)
 		/*
 		 * 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 @@ static int tty_open(struct inode *inode, struct file *filp)
 	    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 @@ static int __tty_fasync(int fd, struct file *filp, int on)
 
 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);

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 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 	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 @@ void tty_ldisc_hangup(struct tty_struct *tty)
 		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 */

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);

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);
 

include/linux/tty.h

@@ -268,7 +268,6 @@ struct tty_struct {
 	struct mutex ldisc_mutex;
 	struct tty_ldisc *ldisc;
 
-	struct mutex legacy_mutex;
 	struct mutex termios_mutex;
 	spinlock_t ctrl_lock;
 	/* Termios values are protected by the termios mutex */
@@ -606,12 +605,8 @@ extern long vt_compat_ioctl(struct tty_struct *tty,
 
 /* tty_mutex.c */
 /* functions for preparation of BKL removal */
-extern void __lockfunc tty_lock(struct tty_struct *tty);
-extern void __lockfunc tty_unlock(struct tty_struct *tty);
-extern void __lockfunc tty_lock_pair(struct tty_struct *tty,
-				struct tty_struct *tty2);
-extern void __lockfunc tty_unlock_pair(struct tty_struct *tty,
-				struct tty_struct *tty2);
+extern void __lockfunc tty_lock(void) __acquires(tty_lock);
+extern void __lockfunc tty_unlock(void) __releases(tty_lock);
 
 /*
  * this shall be called only from where BTM is held (like close)
@@ -626,9 +621,9 @@ extern void __lockfunc tty_unlock_pair(struct tty_struct *tty,
 static inline void tty_wait_until_sent_from_close(struct tty_struct *tty,
 		long timeout)
 {
-	tty_unlock(tty); /* tty->ops->close holds the BTM, drop it while waiting */
+	tty_unlock(); /* tty->ops->close holds the BTM, drop it while waiting */
 	tty_wait_until_sent(tty, timeout);
-	tty_lock(tty);
+	tty_lock();
 }
 
 /*
@@ -643,16 +638,16 @@ static inline void tty_wait_until_sent_from_close(struct tty_struct *tty,
  *
  * Do not use in new code.
  */
-#define wait_event_interruptible_tty(tty, wq, condition)		\
+#define wait_event_interruptible_tty(wq, condition)			\
 ({									\
 	int __ret = 0;							\
 	if (!(condition)) {						\
-		__wait_event_interruptible_tty(tty, wq, condition, __ret);	\
+		__wait_event_interruptible_tty(wq, condition, __ret);	\
 	}								\
 	__ret;								\
 })
 
-#define __wait_event_interruptible_tty(tty, wq, condition, ret)		\
+#define __wait_event_interruptible_tty(wq, condition, ret)		\
 do {									\
 	DEFINE_WAIT(__wait);						\
 									\
@@ -661,9 +656,9 @@ do {									\
 		if (condition)						\
 			break;						\
 		if (!signal_pending(current)) {				\
-			tty_unlock(tty);					\
+			tty_unlock();					\
 			schedule();					\
-			tty_lock(tty);					\
+			tty_lock();					\
 			continue;					\
 		}							\
 		ret = -ERESTARTSYS;					\

net/bluetooth/rfcomm/tty.c

@@ -710,9 +710,9 @@ static int rfcomm_tty_open(struct tty_struct *tty, struct file *filp)
 			break;
 		}
 
-		tty_unlock(tty);
+		tty_unlock();
 		schedule();
-		tty_lock(tty);
+		tty_lock();
 	}
 	set_current_state(TASK_RUNNING);
 	remove_wait_queue(&dev->wait, &wait);