tty: replace BKL with a new tty_lock

As a preparation for replacing the big kernel lock
in the TTY layer, wrap all the callers in new
macros tty_lock, tty_lock_nested and tty_unlock.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 64 insertions, 51 deletions

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 507441ac6edb..5ee9081a560f 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -149,6 +149,7 @@ static long tty_compat_ioctl(struct file *file, unsigned int cmd,
 #else
 #define tty_compat_ioctl NULL
 #endif
+static int __tty_fasync(int fd, struct file *filp, int on);
 static int tty_fasync(int fd, struct file *filp, int on);
 static void release_tty(struct tty_struct *tty, int idx);
 static void __proc_set_tty(struct task_struct *tsk, struct tty_struct *tty);
@@ -483,7 +484,7 @@ EXPORT_SYMBOL_GPL(tty_wakeup);
  *	remains intact.
  *
  *	Locking:
- *		BKL
+ *		BTM
  *		  redirect lock for undoing redirection
  *		  file list lock for manipulating list of ttys
  *		  tty_ldisc_lock from called functions
@@ -513,8 +514,11 @@ static void do_tty_hangup(struct work_struct *work)
 	}
 	spin_unlock(&redirect_lock);
 
-	/* inuse_filps is protected by the single kernel lock */
-	lock_kernel();
+	/* inuse_filps is protected by the single tty lock,
+	   this really needs to change if we want to flush the
+	   workqueue with the lock held */
+	tty_lock_nested(); /* called with BTM held from pty_close and
+				others */
 	check_tty_count(tty, "do_tty_hangup");
 
 	file_list_lock();
@@ -525,7 +529,7 @@ static void do_tty_hangup(struct work_struct *work)
 		if (filp->f_op->write != tty_write)
 			continue;
 		closecount++;
-		tty_fasync(-1, filp, 0);	/* can't block */
+		__tty_fasync(-1, filp, 0);	/* can't block */
 		filp->f_op = &hung_up_tty_fops;
 	}
 	file_list_unlock();
@@ -594,7 +598,7 @@ static void do_tty_hangup(struct work_struct *work)
 	 */
 	set_bit(TTY_HUPPED, &tty->flags);
 	tty_ldisc_enable(tty);
-	unlock_kernel();
+	tty_unlock();
 	if (f)
 		fput(f);
 }
@@ -696,7 +700,8 @@ static void session_clear_tty(struct pid *session)
  *	exiting; it is 0 if called by the ioctl TIOCNOTTY.
  *
  *	Locking:
- *		BKL is taken for hysterical raisins
+ *		BTM is taken for hysterical raisins, and held when
+ *		  called from no_tty().
  *		  tty_mutex is taken to protect tty
  *		  ->siglock is taken to protect ->signal/->sighand
  *		  tasklist_lock is taken to walk process list for sessions
@@ -714,10 +719,10 @@ void disassociate_ctty(int on_exit)
 	tty = get_current_tty();
 	if (tty) {
 		tty_pgrp = get_pid(tty->pgrp);
-		lock_kernel();
+		tty_lock_nested(); /* see above */
 		if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY)
 			tty_vhangup(tty);
-		unlock_kernel();
+		tty_unlock();
 		tty_kref_put(tty);
 	} else if (on_exit) {
 		struct pid *old_pgrp;
@@ -774,9 +779,9 @@ void disassociate_ctty(int on_exit)
 void no_tty(void)
 {
 	struct task_struct *tsk = current;
-	lock_kernel();
+	tty_lock();
 	disassociate_ctty(0);
-	unlock_kernel();
+	tty_unlock();
 	proc_clear_tty(tsk);
 }
 
@@ -1013,19 +1018,19 @@ out:
  * We don't put it into the syslog queue right now maybe in the future if
  * really needed.
  *
- * We must still hold the BKL and test the CLOSING flag for the moment.
+ * We must still hold the BTM and test the CLOSING flag for the moment.
  */
 
 void tty_write_message(struct tty_struct *tty, char *msg)
 {
 	if (tty) {
 		mutex_lock(&tty->atomic_write_lock);
-		lock_kernel();
+		tty_lock();
 		if (tty->ops->write && !test_bit(TTY_CLOSING, &tty->flags)) {
-			unlock_kernel();
+			tty_unlock();
 			tty->ops->write(tty, msg, strlen(msg));
 		} else
-			unlock_kernel();
+			tty_unlock();
 		tty_write_unlock(tty);
 	}
 	return;
@@ -1208,18 +1213,18 @@ static int tty_driver_install_tty(struct tty_driver *driver,
 	int ret;
 
 	if (driver->ops->install) {
-		lock_kernel();
+		tty_lock_nested(); /* already called with BTM held */
 		ret = driver->ops->install(driver, tty);
-		unlock_kernel();
+		tty_unlock();
 		return ret;
 	}
 
 	if (tty_init_termios(tty) == 0) {
-		lock_kernel();
+		tty_lock_nested();
 		tty_driver_kref_get(driver);
 		tty->count++;
 		driver->ttys[idx] = tty;
-		unlock_kernel();
+		tty_unlock();
 		return 0;
 	}
 	return -ENOMEM;
@@ -1312,14 +1317,15 @@ struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx,
 	struct tty_struct *tty;
 	int retval;
 
-	lock_kernel();
+	tty_lock_nested(); /* always called with tty lock held already */
+
 	/* Check if pty master is being opened multiple times */
 	if (driver->subtype == PTY_TYPE_MASTER &&
 		(driver->flags & TTY_DRIVER_DEVPTS_MEM) && !first_ok) {
-		unlock_kernel();
+		tty_unlock();
 		return ERR_PTR(-EIO);
 	}
-	unlock_kernel();
+	tty_unlock();
 
 	/*
 	 * First time open is complex, especially for PTY devices.
@@ -1363,9 +1369,9 @@ release_mem_out:
 	if (printk_ratelimit())
 		printk(KERN_INFO "tty_init_dev: ldisc open failed, "
 				 "clearing slot %d\n", idx);
-	lock_kernel();
+	tty_lock_nested();
 	release_tty(tty, idx);
-	unlock_kernel();
+	tty_unlock();
 	return ERR_PTR(retval);
 }
 
@@ -1512,10 +1518,10 @@ int tty_release(struct inode *inode, struct file *filp)
 	if (tty_paranoia_check(tty, inode, "tty_release_dev"))
 		return 0;
 
-	lock_kernel();
+	tty_lock();
 	check_tty_count(tty, "tty_release_dev");
 
-	tty_fasync(-1, filp, 0);
+	__tty_fasync(-1, filp, 0);
 
 	idx = tty->index;
 	pty_master = (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
@@ -1527,18 +1533,18 @@ int tty_release(struct inode *inode, struct file *filp)
 	if (idx < 0 || idx >= tty->driver->num) {
 		printk(KERN_DEBUG "tty_release_dev: bad idx when trying to "
 				  "free (%s)\n", tty->name);
-		unlock_kernel();
+		tty_unlock();
 		return 0;
 	}
 	if (!devpts) {
 		if (tty != tty->driver->ttys[idx]) {
-			unlock_kernel();
+			tty_unlock();
 			printk(KERN_DEBUG "tty_release_dev: driver.table[%d] not tty "
 			       "for (%s)\n", idx, tty->name);
 			return 0;
 		}
 		if (tty->termios != tty->driver->termios[idx]) {
-			unlock_kernel();
+			tty_unlock();
 			printk(KERN_DEBUG "tty_release_dev: driver.termios[%d] not termios "
 			       "for (%s)\n",
 			       idx, tty->name);
@@ -1556,21 +1562,21 @@ int tty_release(struct inode *inode, struct file *filp)
 	if (tty->driver->other &&
 	     !(tty->driver->flags & TTY_DRIVER_DEVPTS_MEM)) {
 		if (o_tty != tty->driver->other->ttys[idx]) {
-			unlock_kernel();
+			tty_unlock();
 			printk(KERN_DEBUG "tty_release_dev: other->table[%d] "
 					  "not o_tty for (%s)\n",
 			       idx, tty->name);
 			return 0 ;
 		}
 		if (o_tty->termios != tty->driver->other->termios[idx]) {
-			unlock_kernel();
+			tty_unlock();
 			printk(KERN_DEBUG "tty_release_dev: other->termios[%d] "
 					  "not o_termios for (%s)\n",
 			       idx, tty->name);
 			return 0;
 		}
 		if (o_tty->link != tty) {
-			unlock_kernel();
+			tty_unlock();
 			printk(KERN_DEBUG "tty_release_dev: bad pty pointers\n");
 			return 0;
 		}
@@ -1579,7 +1585,7 @@ int tty_release(struct inode *inode, struct file *filp)
 	if (tty->ops->close)
 		tty->ops->close(tty, filp);
 
-	unlock_kernel();
+	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
@@ -1602,7 +1608,7 @@ int tty_release(struct inode *inode, struct file *filp)
 		   opens on /dev/tty */
 
 		mutex_lock(&tty_mutex);
-		lock_kernel();
+		tty_lock();
 		tty_closing = tty->count <= 1;
 		o_tty_closing = o_tty &&
 			(o_tty->count <= (pty_master ? 1 : 0));
@@ -1633,7 +1639,7 @@ int tty_release(struct inode *inode, struct file *filp)
 
 		printk(KERN_WARNING "tty_release_dev: %s: read/write wait queue "
 				    "active!\n", tty_name(tty, buf));
-		unlock_kernel();
+		tty_unlock();
 		mutex_unlock(&tty_mutex);
 		schedule();
 	}
@@ -1698,7 +1704,7 @@ int tty_release(struct inode *inode, struct file *filp)
 
 	/* check whether both sides are closing ... */
 	if (!tty_closing || (o_tty && !o_tty_closing)) {
-		unlock_kernel();
+		tty_unlock();
 		return 0;
 	}
 
@@ -1718,7 +1724,7 @@ int tty_release(struct inode *inode, struct file *filp)
 	/* Make this pty number available for reallocation */
 	if (devpts)
 		devpts_kill_index(inode, idx);
-	unlock_kernel();
+	tty_unlock();
 	return 0;
 }
 
@@ -1760,12 +1766,12 @@ retry_open:
 	retval = 0;
 
 	mutex_lock(&tty_mutex);
-	lock_kernel();
+	tty_lock();
 
 	if (device == MKDEV(TTYAUX_MAJOR, 0)) {
 		tty = get_current_tty();
 		if (!tty) {
-			unlock_kernel();
+			tty_unlock();
 			mutex_unlock(&tty_mutex);
 			return -ENXIO;
 		}
@@ -1797,14 +1803,14 @@ retry_open:
 				goto got_driver;
 			}
 		}
-		unlock_kernel();
+		tty_unlock();
 		mutex_unlock(&tty_mutex);
 		return -ENODEV;
 	}
 
 	driver = get_tty_driver(device, &index);
 	if (!driver) {
-		unlock_kernel();
+		tty_unlock();
 		mutex_unlock(&tty_mutex);
 		return -ENODEV;
 	}
@@ -1814,7 +1820,7 @@ got_driver:
 		tty = tty_driver_lookup_tty(driver, inode, index);
 
 		if (IS_ERR(tty)) {
-			unlock_kernel();
+			tty_unlock();
 			mutex_unlock(&tty_mutex);
 			return PTR_ERR(tty);
 		}
@@ -1830,7 +1836,7 @@ got_driver:
 	mutex_unlock(&tty_mutex);
 	tty_driver_kref_put(driver);
 	if (IS_ERR(tty)) {
-		unlock_kernel();
+		tty_unlock();
 		return PTR_ERR(tty);
 	}
 
@@ -1862,11 +1868,11 @@ got_driver:
 #endif
 		tty_release(inode, filp);
 		if (retval != -ERESTARTSYS) {
-			unlock_kernel();
+			tty_unlock();
 			return retval;
 		}
 		if (signal_pending(current)) {
-			unlock_kernel();
+			tty_unlock();
 			return retval;
 		}
 		schedule();
@@ -1875,14 +1881,14 @@ got_driver:
 		 */
 		if (filp->f_op == &hung_up_tty_fops)
 			filp->f_op = &tty_fops;
-		unlock_kernel();
+		tty_unlock();
 		goto retry_open;
 	}
-	unlock_kernel();
+	tty_unlock();
 
 
 	mutex_lock(&tty_mutex);
-	lock_kernel();
+	tty_lock();
 	spin_lock_irq(&current->sighand->siglock);
 	if (!noctty &&
 	    current->signal->leader &&
@@ -1890,7 +1896,7 @@ got_driver:
 	    tty->session == NULL)
 		__proc_set_tty(current, tty);
 	spin_unlock_irq(&current->sighand->siglock);
-	unlock_kernel();
+	tty_unlock();
 	mutex_unlock(&tty_mutex);
 	return 0;
 }
@@ -1926,13 +1932,12 @@ static unsigned int tty_poll(struct file *filp, poll_table *wait)
 	return ret;
 }
 
-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;
 	unsigned long flags;
 	int retval = 0;
 
-	lock_kernel();
 	tty = (struct tty_struct *)filp->private_data;
 	if (tty_paranoia_check(tty, filp->f_path.dentry->d_inode, "tty_fasync"))
 		goto out;
@@ -1966,7 +1971,15 @@ static int tty_fasync(int fd, struct file *filp, int on)
 	}
 	retval = 0;
 out:
-	unlock_kernel();
+	return retval;
+}
+
+static int tty_fasync(int fd, struct file *filp, int on)
+{
+	int retval;
+	tty_lock();
+	retval = __tty_fasync(fd, filp, on);
+	tty_unlock();
 	return retval;
 }