[PATCH 28/31] tty: remove tty_lock_nested

[Arnd Bergmann <arnd@arndb.de>]

This changes all remaining users of tty_lock_nested
to be non-recursive, which lets us kill this function.
As a consequence, we won't need to keep the lock count
any more, which allows more simplifications later.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/char/pty.c       |    2 +-
 drivers/char/selection.c |    4 ++--
 drivers/char/tty_io.c    |   41 ++++++++++++++++++++---------------------
 drivers/char/tty_ldisc.c |    3 +--
 include/linux/tty.h      |   16 +---------------
 5 files changed, 25 insertions(+), 41 deletions(-)

diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index d9c1407..c9af9ff 100644
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -62,7 +62,7 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
 		if (tty->driver == ptm_driver)
 			devpts_pty_kill(tty->link);
 #endif
-		tty_vhangup(tty->link);
+		tty_vhangup_locked(tty->link);
 	}
 }
 
diff --git a/drivers/char/selection.c b/drivers/char/selection.c
index 75889cd..ebae344 100644
--- a/drivers/char/selection.c
+++ b/drivers/char/selection.c
@@ -313,7 +313,8 @@ int paste_selection(struct tty_struct *tty)
 	struct  tty_ldisc *ld;
 	DECLARE_WAITQUEUE(wait, current);
 
-	tty_lock_nested(); /* always called with BTM from vt_ioctl */
+	/* always called with BTM from vt_ioctl */
+	WARN_ON(!tty_locked());
 
 	acquire_console_sem();
 	poke_blanked_console();
@@ -343,6 +344,5 @@ int paste_selection(struct tty_struct *tty)
 	__set_current_state(TASK_RUNNING);
 
 	tty_ldisc_deref(ld);
-	tty_unlock();
 	return 0;
 }
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index d51993b..5db354d 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -492,10 +492,8 @@ EXPORT_SYMBOL_GPL(tty_wakeup);
  *		  tasklist_lock to walk task list for hangup event
  *		    ->siglock to protect ->signal/->sighand
  */
-static void do_tty_hangup(struct work_struct *work)
+void tty_vhangup_locked(struct tty_struct *tty)
 {
-	struct tty_struct *tty =
-		container_of(work, struct tty_struct, hangup_work);
 	struct file *cons_filp = NULL;
 	struct file *filp, *f = NULL;
 	struct task_struct *p;
@@ -517,8 +515,6 @@ static void do_tty_hangup(struct work_struct *work)
 	/* 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();
@@ -598,11 +594,20 @@ static void do_tty_hangup(struct work_struct *work)
 	 */
 	set_bit(TTY_HUPPED, &tty->flags);
 	tty_ldisc_enable(tty);
-	tty_unlock();
 	if (f)
 		fput(f);
 }
 
+static void do_tty_hangup(struct work_struct *work)
+{
+	struct tty_struct *tty =
+		container_of(work, struct tty_struct, hangup_work);
+
+	tty_lock();
+	tty_vhangup_locked(tty);
+	tty_unlock();
+}
+
 /**
  *	tty_hangup		-	trigger a hangup event
  *	@tty: tty to hangup
@@ -638,7 +643,9 @@ void tty_vhangup(struct tty_struct *tty)
 
 	printk(KERN_DEBUG "%s vhangup...\n", tty_name(tty, buf));
 #endif
-	do_tty_hangup(&tty->hangup_work);
+	tty_lock();
+	tty_vhangup_locked(tty);
+	tty_unlock();
 }
 
 EXPORT_SYMBOL(tty_vhangup);
@@ -719,10 +726,12 @@ void disassociate_ctty(int on_exit)
 	tty = get_current_tty();
 	if (tty) {
 		tty_pgrp = get_pid(tty->pgrp);
-		tty_lock_nested(); /* see above */
-		if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY)
-			tty_vhangup(tty);
-		tty_unlock();
+		if (on_exit) {
+			tty_lock();
+			if (tty->driver->type != TTY_DRIVER_TYPE_PTY)
+				tty_vhangup_locked(tty);
+			tty_unlock();
+		}
 		tty_kref_put(tty);
 	} else if (on_exit) {
 		struct pid *old_pgrp;
@@ -1213,18 +1222,14 @@ static int tty_driver_install_tty(struct tty_driver *driver,
 	int ret;
 
 	if (driver->ops->install) {
-		tty_lock_nested(); /* already called with BTM held */
 		ret = driver->ops->install(driver, tty);
-		tty_unlock();
 		return ret;
 	}
 
 	if (tty_init_termios(tty) == 0) {
-		tty_lock_nested();
 		tty_driver_kref_get(driver);
 		tty->count++;
 		driver->ttys[idx] = tty;
-		tty_unlock();
 		return 0;
 	}
 	return -ENOMEM;
@@ -1317,15 +1322,11 @@ struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx,
 	struct tty_struct *tty;
 	int retval;
 
-	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) {
-		tty_unlock();
 		return ERR_PTR(-EIO);
 	}
-	tty_unlock();
 
 	/*
 	 * First time open is complex, especially for PTY devices.
@@ -1369,9 +1370,7 @@ release_mem_out:
 	if (printk_ratelimit())
 		printk(KERN_INFO "tty_init_dev: ldisc open failed, "
 				 "clearing slot %d\n", idx);
-	tty_lock_nested();
 	release_tty(tty, idx);
-	tty_unlock();
 	return ERR_PTR(retval);
 }
 
diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
index 0f49479..412f977 100644
--- a/drivers/char/tty_ldisc.c
+++ b/drivers/char/tty_ldisc.c
@@ -450,9 +450,8 @@ static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
 	if (ld->ops->open) {
 		int ret;
                 /* BTM here locks versus a hangup event */
-		tty_lock_nested(); /* always held here already */
+		WARN_ON(!tty_locked());
 		ret = ld->ops->open(tty);
-		tty_unlock();
 		return ret;
 	}
 	return 0;
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 18a7955..21a6de2 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -416,6 +416,7 @@ extern int is_ignored(int sig);
 extern int tty_signal(int sig, struct tty_struct *tty);
 extern void tty_hangup(struct tty_struct *tty);
 extern void tty_vhangup(struct tty_struct *tty);
+extern void tty_vhangup_locked(struct tty_struct *tty);
 extern void tty_vhangup_self(void);
 extern void tty_unhangup(struct file *filp);
 extern int tty_hung_up_p(struct file *filp);
@@ -574,21 +575,6 @@ extern long vt_compat_ioctl(struct tty_struct *tty, struct file * file,
 		     unsigned int cmd, unsigned long arg);
 
 /* functions for preparation of BKL removal */
-
-/*
- * tty_lock_nested get the tty_lock while potentially holding it
- *
- * The Big TTY Mutex is a recursive lock, meaning you can take it
- * from a thread that is already holding it.
- * This is bad for a number of reasons, so tty_lock_nested should
- * really be used as rarely as possible. If a code location can
- * be shown to never get called with this held already, it should
- * use tty_lock() instead.
- */
-static inline void __lockfunc tty_lock_nested(void) __acquires(kernel_lock)
-{
-	lock_kernel();
-}
 static inline void tty_lock(void) __acquires(kernel_lock)
 {
 #ifdef CONFIG_LOCK_KERNEL
-- 
1.7.0.4