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>

1 files changed, 40 insertions, 27 deletions

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index ac96f74573d..ca7c25d9f6d 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -185,6 +185,7 @@ 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);
 }
 
@@ -573,7 +574,7 @@ 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);
@@ -666,7 +667,7 @@ 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);
@@ -1103,12 +1104,12 @@ 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);
@@ -1631,7 +1636,7 @@ 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);
@@ -1640,10 +1645,11 @@ 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;
 	}
 
@@ -1655,7 +1661,7 @@ 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
@@ -1678,7 +1684,7 @@ 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));
@@ -1709,7 +1715,7 @@ 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();
 	}
@@ -1772,7 +1778,7 @@ 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();
+		tty_unlock_pair(tty, o_tty);
 		return 0;
 	}
 
@@ -1785,14 +1791,16 @@ 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).
 	 */
 	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;
 }
 
@@ -1896,6 +1904,9 @@ 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)
@@ -1919,8 +1930,7 @@ 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);
@@ -1941,17 +1951,19 @@ 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;
 	}
@@ -1980,7 +1992,7 @@ 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;
@@ -1992,17 +2004,15 @@ 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 &&
@@ -2010,11 +2020,10 @@ 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))
@@ -2097,10 +2106,13 @@ 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;
 }
 
@@ -2937,6 +2949,7 @@ 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);