[RFC PATCH 0/5] tty BKL pushdown

[RFC PATCH 0/5] tty BKL pushdown

[Alan Cox]

First steps to pushing the BKL down further into the tty layer. For review and
analysis not application !

---

Alan Cox (5):
      tty: split the lock up a bit further
      tty: Move the leader test in disassociate
      tty: Push the bkl down a bit in the hangup code
      tty: Push the lock down further into the ldisc code
      tty: push the BKL down into the handlers a bit


 drivers/char/pty.c       |    2 -
 drivers/char/tty_io.c    |  150 ++++++++++++++++++++++++++--------------------
 drivers/char/tty_ldisc.c |   23 ++++++-
 include/linux/tty.h      |    2 -
 kernel/exit.c            |    2 -
 5 files changed, 109 insertions(+), 70 deletions(-)

[RFC PATCH 1/5] tty: push the BKL down into the handlers a bit

[Alan Cox]

Start trying to untangle the remaining BKL mess

Signed-off-by: Alan "I must be out of my tree" Cox <alan@linux.intel.com>
---

 drivers/char/pty.c       |    2 -
 drivers/char/tty_io.c    |  140 ++++++++++++++++++++++++++--------------------
 drivers/char/tty_ldisc.c |   13 ++++
 include/linux/tty.h      |    2 -
 4 files changed, 94 insertions(+), 63 deletions(-)


diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index d516e9c..169cdcc 100644
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -659,7 +659,7 @@ static int __ptmx_open(struct inode *inode, struct file *filp)
 	if (!retval)
 		return 0;
 out1:
-	tty_release_dev(filp);
+	tty_release(inode, filp);
 	return retval;
 out:
 	devpts_kill_index(inode, index);
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 59499ee..05e94a2 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -142,7 +142,6 @@ ssize_t redirected_tty_write(struct file *, const char __user *,
 							size_t, loff_t *);
 static unsigned int tty_poll(struct file *, poll_table *);
 static int tty_open(struct inode *, struct file *);
-static int tty_release(struct inode *, struct file *);
 long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
 #ifdef CONFIG_COMPAT
 static long tty_compat_ioctl(struct file *file, unsigned int cmd,
@@ -1017,14 +1016,16 @@ out:
 
 void tty_write_message(struct tty_struct *tty, char *msg)
 {
-	lock_kernel();
 	if (tty) {
 		mutex_lock(&tty->atomic_write_lock);
-		if (tty->ops->write && !test_bit(TTY_CLOSING, &tty->flags))
+		lock_kernel();
+		if (tty->ops->write && !test_bit(TTY_CLOSING, &tty->flags)) {
+			unlock_kernel();
 			tty->ops->write(tty, msg, strlen(msg));
+		} else
+			unlock_kernel();
 		tty_write_unlock(tty);
 	}
-	unlock_kernel();
 	return;
 }
 
@@ -1202,14 +1203,21 @@ static int tty_driver_install_tty(struct tty_driver *driver,
 						struct tty_struct *tty)
 {
 	int idx = tty->index;
+	int ret;
 
-	if (driver->ops->install)
-		return driver->ops->install(driver, tty);
+	if (driver->ops->install) {
+		lock_kernel();
+		ret = driver->ops->install(driver, tty);
+		unlock_kernel();
+		return ret;
+	}
 
 	if (tty_init_termios(tty) == 0) {
+		lock_kernel();
 		tty_driver_kref_get(driver);
 		tty->count++;
 		driver->ttys[idx] = tty;
+		unlock_kernel();
 		return 0;
 	}
 	return -ENOMEM;
@@ -1302,10 +1310,14 @@ struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx,
 	struct tty_struct *tty;
 	int retval;
 
+	lock_kernel();
 	/* Check if pty master is being opened multiple times */
 	if (driver->subtype == PTY_TYPE_MASTER &&
-		(driver->flags & TTY_DRIVER_DEVPTS_MEM) && !first_ok)
+		(driver->flags & TTY_DRIVER_DEVPTS_MEM) && !first_ok) {
+		unlock_kernel();
 		return ERR_PTR(-EIO);
+	}
+	unlock_kernel();
 
 	/*
 	 * First time open is complex, especially for PTY devices.
@@ -1335,8 +1347,9 @@ struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx,
 	 * If we fail here just call release_tty to clean up.  No need
 	 * to decrement the use counts, as release_tty doesn't care.
 	 */
-
+	lock_kernel();
 	retval = tty_ldisc_setup(tty, tty->link);
+	unlock_kernel();
 	if (retval)
 		goto release_mem_out;
 	return tty;
@@ -1350,7 +1363,9 @@ release_mem_out:
 	if (printk_ratelimit())
 		printk(KERN_INFO "tty_init_dev: ldisc open failed, "
 				 "clearing slot %d\n", idx);
+	lock_kernel();
 	release_tty(tty, idx);
+	unlock_kernel();
 	return ERR_PTR(retval);
 }
 
@@ -1464,7 +1479,17 @@ static void release_tty(struct tty_struct *tty, int idx)
 	tty_kref_put(tty);
 }
 
-/*
+/**
+ *	tty_release		-	vfs callback for close
+ *	@inode: inode of tty
+ *	@filp: file pointer for handle to tty
+ *
+ *	Called the last time each file handle is closed that references
+ *	this tty. There may however be several such references.
+ *
+ *	Locking:
+ *		Takes bkl. See tty_release_dev
+ *
  * Even releasing the tty structures is a tricky business.. We have
  * to be very careful that the structures are all released at the
  * same time, as interrupts might otherwise get the wrong pointers.
@@ -1472,20 +1497,20 @@ static void release_tty(struct tty_struct *tty, int idx)
  * WSH 09/09/97: rewritten to avoid some nasty race conditions that could
  * lead to double frees or releasing memory still in use.
  */
-void tty_release_dev(struct file *filp)
+
+int tty_release(struct inode *inode, struct file *filp)
 {
 	struct tty_struct *tty, *o_tty;
 	int	pty_master, tty_closing, o_tty_closing, do_sleep;
 	int	devpts;
 	int	idx;
 	char	buf[64];
-	struct 	inode *inode;
 
-	inode = filp->f_path.dentry->d_inode;
 	tty = (struct tty_struct *)filp->private_data;
 	if (tty_paranoia_check(tty, inode, "tty_release_dev"))
-		return;
+		return 0;
 
+	lock_kernel();
 	check_tty_count(tty, "tty_release_dev");
 
 	tty_fasync(-1, filp, 0);
@@ -1500,19 +1525,22 @@ void tty_release_dev(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);
-		return;
+		unlock_kernel();
+		return 0;
 	}
 	if (!devpts) {
 		if (tty != tty->driver->ttys[idx]) {
+			unlock_kernel();
 			printk(KERN_DEBUG "tty_release_dev: driver.table[%d] not tty "
 			       "for (%s)\n", idx, tty->name);
-			return;
+			return 0;
 		}
 		if (tty->termios != tty->driver->termios[idx]) {
+			unlock_kernel();
 			printk(KERN_DEBUG "tty_release_dev: driver.termios[%d] not termios "
 			       "for (%s)\n",
 			       idx, tty->name);
-			return;
+			return 0;
 		}
 	}
 #endif
@@ -1526,26 +1554,29 @@ void tty_release_dev(struct file *filp)
 	if (tty->driver->other &&
 	     !(tty->driver->flags & TTY_DRIVER_DEVPTS_MEM)) {
 		if (o_tty != tty->driver->other->ttys[idx]) {
+			unlock_kernel();
 			printk(KERN_DEBUG "tty_release_dev: other->table[%d] "
 					  "not o_tty for (%s)\n",
 			       idx, tty->name);
-			return;
+			return 0 ;
 		}
 		if (o_tty->termios != tty->driver->other->termios[idx]) {
+			unlock_kernel();
 			printk(KERN_DEBUG "tty_release_dev: other->termios[%d] "
 					  "not o_termios for (%s)\n",
 			       idx, tty->name);
-			return;
+			return 0;
 		}
 		if (o_tty->link != tty) {
 			printk(KERN_DEBUG "tty_release_dev: bad pty pointers\n");
-			return;
+			return 0;
 		}
 	}
 #endif
 	if (tty->ops->close)
 		tty->ops->close(tty, filp);
 
+	unlock_kernel();
 	/*
 	 * 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
@@ -1568,6 +1599,7 @@ void tty_release_dev(struct file *filp)
 		   opens on /dev/tty */
 
 		mutex_lock(&tty_mutex);
+		lock_kernel();
 		tty_closing = tty->count <= 1;
 		o_tty_closing = o_tty &&
 			(o_tty->count <= (pty_master ? 1 : 0));
@@ -1598,6 +1630,7 @@ void tty_release_dev(struct file *filp)
 
 		printk(KERN_WARNING "tty_release_dev: %s: read/write wait queue "
 				    "active!\n", tty_name(tty, buf));
+		unlock_kernel();
 		mutex_unlock(&tty_mutex);
 		schedule();
 	}
@@ -1661,8 +1694,10 @@ void tty_release_dev(struct file *filp)
 	mutex_unlock(&tty_mutex);
 
 	/* check whether both sides are closing ... */
-	if (!tty_closing || (o_tty && !o_tty_closing))
-		return;
+	if (!tty_closing || (o_tty && !o_tty_closing)) {
+		unlock_kernel();
+		return 0;
+	}
 
 #ifdef TTY_DEBUG_HANGUP
 	printk(KERN_DEBUG "freeing tty structure...");
@@ -1680,10 +1715,12 @@ void tty_release_dev(struct file *filp)
 	/* Make this pty number available for reallocation */
 	if (devpts)
 		devpts_kill_index(inode, idx);
+	unlock_kernel();
+	return 0;
 }
 
 /**
- *	__tty_open		-	open a tty device
+ *	tty_open		-	open a tty device
  *	@inode: inode of device file
  *	@filp: file pointer to tty
  *
@@ -1703,7 +1740,7 @@ void tty_release_dev(struct file *filp)
  *		 ->siglock protects ->signal/->sighand
  */
 
-static int __tty_open(struct inode *inode, struct file *filp)
+static int tty_open(struct inode *inode, struct file *filp)
 {
 	struct tty_struct *tty = NULL;
 	int noctty, retval;
@@ -1720,10 +1757,12 @@ retry_open:
 	retval = 0;
 
 	mutex_lock(&tty_mutex);
+	lock_kernel();
 
 	if (device == MKDEV(TTYAUX_MAJOR, 0)) {
 		tty = get_current_tty();
 		if (!tty) {
+			unlock_kernel();
 			mutex_unlock(&tty_mutex);
 			return -ENXIO;
 		}
@@ -1755,12 +1794,14 @@ retry_open:
 				goto got_driver;
 			}
 		}
+		unlock_kernel();
 		mutex_unlock(&tty_mutex);
 		return -ENODEV;
 	}
 
 	driver = get_tty_driver(device, &index);
 	if (!driver) {
+		unlock_kernel();
 		mutex_unlock(&tty_mutex);
 		return -ENODEV;
 	}
@@ -1770,6 +1811,7 @@ got_driver:
 		tty = tty_driver_lookup_tty(driver, inode, index);
 
 		if (IS_ERR(tty)) {
+			unlock_kernel();
 			mutex_unlock(&tty_mutex);
 			return PTR_ERR(tty);
 		}
@@ -1784,8 +1826,10 @@ got_driver:
 
 	mutex_unlock(&tty_mutex);
 	tty_driver_kref_put(driver);
-	if (IS_ERR(tty))
+	if (IS_ERR(tty)) {
+		unlock_kernel();
 		return PTR_ERR(tty);
+	}
 
 	filp->private_data = tty;
 	file_move(filp, &tty->tty_files);
@@ -1813,11 +1857,15 @@ got_driver:
 		printk(KERN_DEBUG "error %d in opening %s...", retval,
 		       tty->name);
 #endif
-		tty_release_dev(filp);
-		if (retval != -ERESTARTSYS)
+		tty_release(inode, filp);
+		if (retval != -ERESTARTSYS) {
+			unlock_kernel();
 			return retval;
-		if (signal_pending(current))
+		}
+		if (signal_pending(current)) {
+			unlock_kernel();
 			return retval;
+		}
 		schedule();
 		/*
 		 * Need to reset f_op in case a hangup happened.
@@ -1826,8 +1874,11 @@ got_driver:
 			filp->f_op = &tty_fops;
 		goto retry_open;
 	}
+	unlock_kernel();
+
 
 	mutex_lock(&tty_mutex);
+	lock_kernel();
 	spin_lock_irq(&current->sighand->siglock);
 	if (!noctty &&
 	    current->signal->leader &&
@@ -1835,44 +1886,13 @@ got_driver:
 	    tty->session == NULL)
 		__proc_set_tty(current, tty);
 	spin_unlock_irq(&current->sighand->siglock);
+	unlock_kernel();
 	mutex_unlock(&tty_mutex);
 	return 0;
 }
 
-/* BKL pushdown: scary code avoidance wrapper */
-static int tty_open(struct inode *inode, struct file *filp)
-{
-	int ret;
-
-	lock_kernel();
-	ret = __tty_open(inode, filp);
-	unlock_kernel();
-	return ret;
-}
 
 
-
-
-/**
- *	tty_release		-	vfs callback for close
- *	@inode: inode of tty
- *	@filp: file pointer for handle to tty
- *
- *	Called the last time each file handle is closed that references
- *	this tty. There may however be several such references.
- *
- *	Locking:
- *		Takes bkl. See tty_release_dev
- */
-
-static int tty_release(struct inode *inode, struct file *filp)
-{
-	lock_kernel();
-	tty_release_dev(filp);
-	unlock_kernel();
-	return 0;
-}
-
 /**
  *	tty_poll	-	check tty status
  *	@filp: file being polled
@@ -2317,9 +2337,7 @@ static int tiocsetd(struct tty_struct *tty, int __user *p)
 	if (get_user(ldisc, p))
 		return -EFAULT;
 
-	lock_kernel();
 	ret = tty_set_ldisc(tty, ldisc);
-	unlock_kernel();
 
 	return ret;
 }
diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
index feb5507..d914e77 100644
--- a/drivers/char/tty_ldisc.c
+++ b/drivers/char/tty_ldisc.c
@@ -34,6 +34,8 @@
 #include <linux/vt_kern.h>
 #include <linux/selection.h>
 
+#include <linux/smp_lock.h>	/* For the moment */
+
 #include <linux/kmod.h>
 #include <linux/nsproxy.h>
 
@@ -545,6 +547,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 	if (IS_ERR(new_ldisc))
 		return PTR_ERR(new_ldisc);
 
+	lock_kernel();
 	/*
 	 *	We need to look at the tty locking here for pty/tty pairs
 	 *	when both sides try to change in parallel.
@@ -558,6 +561,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 	 */
 
 	if (tty->ldisc->ops->num == ldisc) {
+		unlock_kernel();
 		tty_ldisc_put(new_ldisc);
 		return 0;
 	}
@@ -569,6 +573,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
 	tty_wait_until_sent(tty, 0);
 
+	unlock_kernel();
 	mutex_lock(&tty->ldisc_mutex);
 
 	/*
@@ -582,6 +587,9 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 			test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
 		mutex_lock(&tty->ldisc_mutex);
 	}
+
+	lock_kernel();
+
 	set_bit(TTY_LDISC_CHANGING, &tty->flags);
 
 	/*
@@ -592,6 +600,8 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 	tty->receive_room = 0;
 
 	o_ldisc = tty->ldisc;
+
+	unlock_kernel();
 	/*
 	 *	Make sure we don't change while someone holds a
 	 *	reference to the line discipline. The TTY_LDISC bit
@@ -617,12 +627,14 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 	flush_scheduled_work();
 
 	mutex_lock(&tty->ldisc_mutex);
+	lock_kernel();
 	if (test_bit(TTY_HUPPED, &tty->flags)) {
 		/* We were raced by the hangup method. It will have stomped
 		   the ldisc data and closed the ldisc down */
 		clear_bit(TTY_LDISC_CHANGING, &tty->flags);
 		mutex_unlock(&tty->ldisc_mutex);
 		tty_ldisc_put(new_ldisc);
+		unlock_kernel();
 		return -EIO;
 	}
 
@@ -664,6 +676,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 	if (o_work)
 		schedule_delayed_work(&o_tty->buf.work, 1);
 	mutex_unlock(&tty->ldisc_mutex);
+	unlock_kernel();
 	return retval;
 }
 
diff --git a/include/linux/tty.h b/include/linux/tty.h
index e6da667..405a903 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -449,7 +449,7 @@ extern void initialize_tty_struct(struct tty_struct *tty,
 		struct tty_driver *driver, int idx);
 extern struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx,
 								int first_ok);
-extern void tty_release_dev(struct file *filp);
+extern int tty_release(struct inode *inode, struct file *filp);
 extern int tty_init_termios(struct tty_struct *tty);
 
 extern struct tty_struct *tty_pair_get_tty(struct tty_struct *tty);

Re: [RFC PATCH 1/5] tty: push the BKL down into the handlers a bit

[Dan Carpenter]

On Wed, Nov 18, 2009 at 02:25:43PM +0000, Alan Cox wrote:
> Start trying to untangle the remaining BKL mess
> 
> Signed-off-by: Alan "I must be out of my tree" Cox <alan@linux.intel.com>
> ---
> 
>  drivers/char/pty.c       |    2 -
>  drivers/char/tty_io.c    |  140 ++++++++++++++++++++++++++--------------------
>  drivers/char/tty_ldisc.c |   13 ++++
>  include/linux/tty.h      |    2 -
>  4 files changed, 94 insertions(+), 63 deletions(-)
> 

  1565                  if (o_tty->termios != tty->driver->other->termios[idx]) {
  1566                          unlock_kernel();
  1567                          printk(KERN_DEBUG "tty_release_dev: other->termios[%d] "
  1568                                            "not o_termios for (%s)\n",
  1569                                 idx, tty->name);
  1570                          return 0;
  1571                  }
  1572                  if (o_tty->link != tty) {

We would need an unlock_kernel() here.

  1573                          printk(KERN_DEBUG "tty_release_dev: bad pty pointers\n");
  1574                          return 0;
  1575                  }

regards,
dan carpenter

[PATCH 2/5] tty: Push the lock down further into the ldisc code

[Alan Cox]

Signed-off-by: Alan Cox <alan@linux.intel.com>
---

 drivers/char/tty_io.c    |    2 --
 drivers/char/tty_ldisc.c |   12 +++++++++---
 2 files changed, 9 insertions(+), 5 deletions(-)


diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 05e94a2..a1b1ff6 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1347,9 +1347,7 @@ struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx,
 	 * If we fail here just call release_tty to clean up.  No need
 	 * to decrement the use counts, as release_tty doesn't care.
 	 */
-	lock_kernel();
 	retval = tty_ldisc_setup(tty, tty->link);
-	unlock_kernel();
 	if (retval)
 		goto release_mem_out;
 	return tty;
diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
index d914e77..3f653f7 100644
--- a/drivers/char/tty_ldisc.c
+++ b/drivers/char/tty_ldisc.c
@@ -445,8 +445,14 @@ static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
 static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
 {
 	WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
-	if (ld->ops->open)
-		return ld->ops->open(tty);
+	if (ld->ops->open) {
+		int ret;
+                /* BKL here locks versus a hangup event */
+		lock_kernel();
+		ret = ld->ops->open(tty);
+		unlock_kernel();
+		return ret;
+	}
 	return 0;
 }
 
@@ -566,6 +572,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 		return 0;
 	}
 
+	unlock_kernel();
 	/*
 	 *	Problem: What do we do if this blocks ?
 	 *	We could deadlock here
@@ -573,7 +580,6 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
 	tty_wait_until_sent(tty, 0);
 
-	unlock_kernel();
 	mutex_lock(&tty->ldisc_mutex);
 
 	/*

[PATCH 3/5] tty: Push the bkl down a bit in the hangup code

[Alan Cox]

We know that the redirect field is handled via its own locking in all
places

Signed-off-by: Alan Cox <alan@linux.intel.com>
---

 drivers/char/tty_io.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)


diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index a1b1ff6..f4a0404 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -505,8 +505,6 @@ static void do_tty_hangup(struct work_struct *work)
 	if (!tty)
 		return;
 
-	/* inuse_filps is protected by the single kernel lock */
-	lock_kernel();
 
 	spin_lock(&redirect_lock);
 	if (redirect && redirect->private_data == tty) {
@@ -515,6 +513,8 @@ static void do_tty_hangup(struct work_struct *work)
 	}
 	spin_unlock(&redirect_lock);
 
+	/* inuse_filps is protected by the single kernel lock */
+	lock_kernel();
 	check_tty_count(tty, "do_tty_hangup");
 	file_list_lock();
 	/* This breaks for file handles being sent over AF_UNIX sockets ? */

[PATCH 4/5] tty: Move the leader test in disassociate

[Alan Cox]

There are two call points, both want to check that tty->signal->leader is
set. Move the test into disassociate_ctty() as that will make locking
changes easier in a bit

Signed-off-by: Alan Cox <alan@linux.intel.com>
---

 drivers/char/tty_io.c |    5 +++--
 kernel/exit.c         |    2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)


diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index f4a0404..aee68f5 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -707,6 +707,8 @@ void disassociate_ctty(int on_exit)
 	struct tty_struct *tty;
 	struct pid *tty_pgrp = NULL;
 
+	if (!current->signal->leader)
+		return;
 
 	tty = get_current_tty();
 	if (tty) {
@@ -772,8 +774,7 @@ void no_tty(void)
 {
 	struct task_struct *tsk = current;
 	lock_kernel();
-	if (tsk->signal->leader)
-		disassociate_ctty(0);
+	disassociate_ctty(0);
 	unlock_kernel();
 	proc_clear_tty(tsk);
 }
diff --git a/kernel/exit.c b/kernel/exit.c
index f7864ac..dbca05b 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -970,7 +970,7 @@ NORET_TYPE void do_exit(long code)
 	exit_thread();
 	cgroup_exit(tsk, 1);
 
-	if (group_dead && tsk->signal->leader)
+	if (group_dead)
 		disassociate_ctty(1);
 
 	module_put(task_thread_info(tsk)->exec_domain->module);

[PATCH 5/5] tty: split the lock up a bit further

[Alan Cox]

The tty count sanity check may need the BKL, that isn't clear. However it
is clear that the count use of the lock is internal and independant of the
bigger use of the lock.

Furthermore the file list locking is also separately locked already

Signed-off-by: Alan Cox <alan@linux.intel.com>
---

 drivers/char/tty_io.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)


diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index aee68f5..4c2f793 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -516,6 +516,8 @@ static void do_tty_hangup(struct work_struct *work)
 	/* inuse_filps is protected by the single kernel lock */
 	lock_kernel();
 	check_tty_count(tty, "do_tty_hangup");
+	unlock_kernel();
+
 	file_list_lock();
 	/* This breaks for file handles being sent over AF_UNIX sockets ? */
 	list_for_each_entry(filp, &tty->tty_files, f_u.fu_list) {
@@ -529,6 +531,7 @@ static void do_tty_hangup(struct work_struct *work)
 	}
 	file_list_unlock();
 
+	lock_kernel();
 	tty_ldisc_hangup(tty);
 
 	read_lock(&tasklist_lock);