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 <[e-mail]>
Cc: Alan Cox <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/char/amiserial.c

···
 	if (!retinfo)
 		return -EFAULT;
 	memset(&tmp, 0, sizeof(tmp));
-	lock_kernel();
+	tty_lock();
 	tmp.type = state->type;
 	tmp.line = state->line;
 	tmp.port = state->port;
···
 	tmp.close_delay = state->close_delay;
 	tmp.closing_wait = state->closing_wait;
 	tmp.custom_divisor = state->custom_divisor;
-	unlock_kernel();
+	tty_unlock();
 	if (copy_to_user(retinfo,&tmp,sizeof(*retinfo)))
 		return -EFAULT;
 	return 0;
···
 	if (copy_from_user(&new_serial,new_info,sizeof(new_serial)))
 		return -EFAULT;
 
-	lock_kernel();
+	tty_lock();
 	state = info->state;
 	old_state = *state;
   
 	change_irq = new_serial.irq != state->irq;
 	change_port = (new_serial.port != state->port);
 	if(change_irq || change_port || (new_serial.xmit_fifo_size != state->xmit_fifo_size)) {
-	  unlock_kernel();
+	  tty_unlock();
 	  return -EINVAL;
 	}
   
···
 	}
 
 	if (new_serial.baud_base < 9600) {
-		unlock_kernel();
+		tty_unlock();
 		return -EINVAL;
 	}
 
···
 		}
 	} else
 		retval = startup(info);
-	unlock_kernel();
+	tty_unlock();
 	return retval;
 }
 
···
 
 	orig_jiffies = jiffies;
 
-	lock_kernel();
+	tty_lock_nested(); /* tty_wait_until_sent is called from lots of places */
 	/*
 	 * Set the check interval to be 1/5 of the estimated time to
 	 * send a single character, and make it at least 1.  The check
···
 			break;
 	}
 	__set_current_state(TASK_RUNNING);
-	unlock_kernel();
+	tty_unlock();
 #ifdef SERIAL_DEBUG_RS_WAIT_UNTIL_SENT
 	printk("lsr = %d (jiff=%lu)...done\n", lsr, jiffies);
 #endif

drivers/char/briq_panel.c

···
 
 static int briq_panel_open(struct inode *ino, struct file *filep)
 {
-	lock_kernel();
+	tty_lock();
 	/* enforce single access, vfd_is_open is protected by BKL */
 	if (vfd_is_open) {
-		unlock_kernel();
+		tty_unlock();
 		return -EBUSY;
 	}
 	vfd_is_open = 1;
 
-	unlock_kernel();
+	tty_unlock();
 	return 0;
 }
 

drivers/char/n_hdlc.c

···
 		return -EFAULT;
 	}
 
-	lock_kernel();
+	tty_lock();
 
 	for (;;) {
 		if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
-			unlock_kernel();
+			tty_unlock();
 			return -EIO;
 		}
 
 		n_hdlc = tty2n_hdlc (tty);
 		if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC ||
 			 tty != n_hdlc->tty) {
-			unlock_kernel();
+			tty_unlock();
 			return 0;
 		}
 
···
 			
 		/* no data */
 		if (file->f_flags & O_NONBLOCK) {
-			unlock_kernel();
+			tty_unlock();
 			return -EAGAIN;
 		}
 			
 		interruptible_sleep_on (&tty->read_wait);
 		if (signal_pending(current)) {
-			unlock_kernel();
+			tty_unlock();
 			return -EINTR;
 		}
 	}
···
 		kfree(rbuf);
 	else	
 		n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,rbuf);
-	unlock_kernel();
+	tty_unlock();
 	return ret;
 	
 }	/* end of n_hdlc_tty_read() */
···
 		count = maxframe;
 	}
 	
-	lock_kernel();
+	tty_lock();
 
 	add_wait_queue(&tty->write_wait, &wait);
 	set_current_state(TASK_INTERRUPTIBLE);
···
 		n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
 		n_hdlc_send_frames(n_hdlc,tty);
 	}
-	unlock_kernel();
+	tty_unlock();
 	return error;
 	
 }	/* end of n_hdlc_tty_write() */

drivers/char/n_r3964.c

···
 
 	TRACE_L("read()");
 
-	lock_kernel();
+	tty_lock();
 
 	pClient = findClient(pInfo, task_pid(current));
 	if (pClient) {
···
 	}
 	ret = -EPERM;
 unlock:
-	unlock_kernel();
+	tty_unlock();
 	return ret;
 }
 
···
 	pHeader->locks = 0;
 	pHeader->owner = NULL;
 
-	lock_kernel();
+	tty_lock();
 
 	pClient = findClient(pInfo, task_pid(current));
 	if (pClient) {
···
 	add_tx_queue(pInfo, pHeader);
 	trigger_transmit(pInfo);
 
-	unlock_kernel();
+	tty_unlock();
 
 	return 0;
 }

drivers/char/pty.c

···
 {
 	int ret;
 
-	lock_kernel();
+	tty_lock();
 	ret = __ptmx_open(inode, filp);
-	unlock_kernel();
+	tty_unlock();
 	return ret;
 }
 

drivers/char/selection.c

···
 	struct  tty_ldisc *ld;
 	DECLARE_WAITQUEUE(wait, current);
 
-	lock_kernel();
+	tty_lock_nested(); /* always called with BTM from vt_ioctl */
 
 	acquire_console_sem();
 	poke_blanked_console();
···
 	__set_current_state(TASK_RUNNING);
 
 	tty_ldisc_deref(ld);
-	unlock_kernel();
+	tty_unlock();
 	return 0;
 }

drivers/char/serial167.c

···
 	printk("cy_ioctl %s, cmd = %x arg = %lx\n", tty->name, cmd, arg);	/* */
 #endif
 
-	lock_kernel();
+	tty_lock();
 
 	switch (cmd) {
 	case CYGETMON:
···
 	default:
 		ret_val = -ENOIOCTLCMD;
 	}
-	unlock_kernel();
+	tty_unlock();
 
 #ifdef SERIAL_DEBUG_OTHER
 	printk("cy_ioctl done\n");

drivers/char/sx.c

···
 	if (!capable(CAP_SYS_RAWIO))
 		return -EPERM;
 
-	lock_kernel();
+	tty_lock();
 
 	sx_dprintk(SX_DEBUG_FIRMWARE, "IOCTL %x: %lx\n", cmd, arg);
 
···
 		break;
 	}
 out:
-	unlock_kernel();
+	tty_unlock();
 	func_exit();
 	return rc;
 }
···
 	int rv;
 
 	func_enter();
-	lock_kernel();
+	tty_lock();
 
 	if (flag)
 		rv = sx_send_command(port, HS_START, -1, HS_IDLE_BREAK);
···
 	if (rv != 1)
 		printk(KERN_ERR "sx: couldn't send break (%x).\n",
 			read_sx_byte(port->board, CHAN_OFFSET(port, hi_hstat)));
-	unlock_kernel();
+	tty_unlock();
 	func_exit();
 	return 0;
 }
···
 	/* func_enter2(); */
 
 	rc = 0;
-	lock_kernel();
+	tty_lock();
 	switch (cmd) {
 	case TIOCGSERIAL:
 		rc = gs_getserial(&port->gs, argp);
···
 		rc = -ENOIOCTLCMD;
 		break;
 	}
-	unlock_kernel();
+	tty_unlock();
 
 	/* func_exit(); */
 	return rc;

drivers/char/tty_io.c

···
 #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);
···
  *	remains intact.
  *
  *	Locking:
- *		BKL
+ *		BTM
  *		  redirect lock for undoing redirection
  *		  file list lock for manipulating list of ttys
  *		  tty_ldisc_lock from called functions
···
 	}
 	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();
···
 		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();
···
 	 */
 	set_bit(TTY_HUPPED, &tty->flags);
 	tty_ldisc_enable(tty);
-	unlock_kernel();
+	tty_unlock();
 	if (f)
 		fput(f);
 }
···
  *	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
···
 	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;
···
 void no_tty(void)
 {
 	struct task_struct *tsk = current;
-	lock_kernel();
+	tty_lock();
 	disassociate_ctty(0);
-	unlock_kernel();
+	tty_unlock();
 	proc_clear_tty(tsk);
 }
 
···
  * 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;
···
 	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;
···
 	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.
···
 	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);
 }
 
···
 	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 &&
···
 	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);
···
 	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;
 		}
···
 	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
···
 		   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));
···
 
 		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();
 	}
···
 
 	/* check whether both sides are closing ... */
 	if (!tty_closing || (o_tty && !o_tty_closing)) {
-		unlock_kernel();
+		tty_unlock();
 		return 0;
 	}
 
···
 	/* Make this pty number available for reallocation */
 	if (devpts)
 		devpts_kill_index(inode, idx);
-	unlock_kernel();
+	tty_unlock();
 	return 0;
 }
 
···
 	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;
 		}
···
 				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;
 	}
···
 		tty = tty_driver_lookup_tty(driver, inode, index);
 
 		if (IS_ERR(tty)) {
-			unlock_kernel();
+			tty_unlock();
 			mutex_unlock(&tty_mutex);
 			return PTR_ERR(tty);
 		}
···
 	mutex_unlock(&tty_mutex);
 	tty_driver_kref_put(driver);
 	if (IS_ERR(tty)) {
-		unlock_kernel();
+		tty_unlock();
 		return PTR_ERR(tty);
 	}
 
···
 #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();
···
 		 */
 		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 &&
···
 	    tty->session == NULL)
 		__proc_set_tty(current, tty);
 	spin_unlock_irq(&current->sighand->siglock);
-	unlock_kernel();
+	tty_unlock();
 	mutex_unlock(&tty_mutex);
 	return 0;
 }
···
 	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;
···
 	}
 	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;
 }
 

drivers/char/tty_ldisc.c

···
  *
  *	A helper opening method. Also a convenient debugging and check
  *	point.
+ *
+ *	Locking: always called with BTM already held.
  */
 
 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) {
 		int ret;
-                /* BKL here locks verus a hangup event */
-		lock_kernel();
+                /* BTM here locks versus a hangup event */
+		tty_lock_nested(); /* always held here already */
 		ret = ld->ops->open(tty);
-		unlock_kernel();
+		tty_unlock();
 		return ret;
 	}
 	return 0;
···
 	if (IS_ERR(new_ldisc))
 		return PTR_ERR(new_ldisc);
 
-	lock_kernel();
+	tty_lock();
 	/*
 	 *	We need to look at the tty locking here for pty/tty pairs
 	 *	when both sides try to change in parallel.
···
 	 */
 
 	if (tty->ldisc->ops->num == ldisc) {
-		unlock_kernel();
+		tty_unlock();
 		tty_ldisc_put(new_ldisc);
 		return 0;
 	}
 
-	unlock_kernel();
+	tty_unlock();
 	/*
 	 *	Problem: What do we do if this blocks ?
 	 *	We could deadlock here
···
 		mutex_lock(&tty->ldisc_mutex);
 	}
 
-	lock_kernel();
+	tty_lock();
 
 	set_bit(TTY_LDISC_CHANGING, &tty->flags);
 
···
 
 	o_ldisc = tty->ldisc;
 
-	unlock_kernel();
+	tty_unlock();
 	/*
 	 *	Make sure we don't change while someone holds a
 	 *	reference to the line discipline. The TTY_LDISC bit
···
 	flush_scheduled_work();
 
 	mutex_lock(&tty->ldisc_mutex);
-	lock_kernel();
+	tty_lock();
 	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();
+		tty_unlock();
 		return -EIO;
 	}
 
···
 	if (o_work)
 		schedule_delayed_work(&o_tty->buf.work, 1);
 	mutex_unlock(&tty->ldisc_mutex);
-	unlock_kernel();
+	tty_unlock();
 	return retval;
 }
 

drivers/char/vc_screen.c

···
 	unsigned int currcons = iminor(inode) & 127;
 	int ret = 0;
 	
-	lock_kernel();
+	tty_lock();
 	if(currcons && !vc_cons_allocated(currcons-1))
 		ret = -ENXIO;
-	unlock_kernel();
+	tty_unlock();
 	return ret;
 }
 

drivers/char/vt_ioctl.c

···
 
 	console = vc->vc_num;
 
-	lock_kernel();
+	tty_lock();
 
 	if (!vc_cons_allocated(console)) { 	/* impossible? */
 		ret = -ENOIOCTLCMD;
···
 		ret = -ENOIOCTLCMD;
 	}
 out:
-	unlock_kernel();
+	tty_unlock();
 	return ret;
 eperm:
 	ret = -EPERM;
···
 
 	console = vc->vc_num;
 
-	lock_kernel();
+	tty_lock();
 
 	if (!vc_cons_allocated(console)) { 	/* impossible? */
 		ret = -ENOIOCTLCMD;
···
 		goto fallback;
 	}
 out:
-	unlock_kernel();
+	tty_unlock();
 	return ret;
 
 fallback:
-	unlock_kernel();
+	tty_unlock();
 	return vt_ioctl(tty, file, cmd, arg);
 }
 

drivers/serial/68360serial.c

···
 	printk("jiff=%lu...", jiffies);
 #endif
 
-	lock_kernel();
+	tty_lock_nested(); /* always held already since we come from ->close */
 	/* We go through the loop at least once because we can't tell
 	 * exactly when the last character exits the shifter.  There can
 	 * be at least two characters waiting to be sent after the buffers
···
 			bdp--;
 	} while (bdp->status & BD_SC_READY);
 	current->state = TASK_RUNNING;
-	unlock_kernel();
+	tty_unlock();
 #ifdef SERIAL_DEBUG_RS_WAIT_UNTIL_SENT
 	printk("lsr = %d (jiff=%lu)...done\n", lsr, jiffies);
 #endif

drivers/serial/crisv10.c

···
 	 * Check R_DMA_CHx_STATUS bit 0-6=number of available bytes in FIFO
 	 * R_DMA_CHx_HWSW bit 31-16=nbr of bytes left in DMA buffer (0=64k)
 	 */
-	lock_kernel();
+	tty_lock_nested(); /* locked already when coming from close */
 	orig_jiffies = jiffies;
 	while (info->xmit.head != info->xmit.tail || /* More in send queue */
 	       (*info->ostatusadr & 0x007f) ||  /* more in FIFO */
···
 			curr_time_usec - info->last_tx_active_usec;
 	}
 	set_current_state(TASK_RUNNING);
-	unlock_kernel();
+	tty_unlock();
 }
 
 /*

drivers/serial/serial_core.c

···
 	struct uart_port *uport;
 	unsigned long flags;
 
-	BUG_ON(!kernel_locked());
+	BUG_ON(!tty_locked());
 
 	if (!state)
 		return;
···
 	if (port->type == PORT_UNKNOWN || port->fifosize == 0)
 		return;
 
-	lock_kernel();
+	tty_lock_nested(); /* already locked when coming from close */
 
 	/*
 	 * Set the check interval to be 1/5 of the estimated time to
···
 			break;
 	}
 	set_current_state(TASK_RUNNING); /* might not be needed */
-	unlock_kernel();
+	tty_unlock();
 }
 
 /*
···
 	struct tty_port *port = &state->port;
 	unsigned long flags;
 
-	BUG_ON(!kernel_locked());
+	BUG_ON(!tty_locked());
 	pr_debug("uart_hangup(%d)\n", state->uart_port->line);
 
 	mutex_lock(&port->mutex);
···
 	struct tty_port *port;
 	int retval, line = tty->index;
 
-	BUG_ON(!kernel_locked());
+	BUG_ON(!tty_locked());
 	pr_debug("uart_open(%d) called\n", line);
 
 	/*

drivers/video/console/vgacon.c

···
 		charmap += 4 * cmapsz;
 #endif
 
-	unlock_kernel();
+	tty_unlock();
 	spin_lock_irq(&vga_lock);
 	/* First, the Sequencer */
 	vga_wseq(state->vgabase, VGA_SEQ_RESET, 0x1);
···
 		vga_wattr(state->vgabase, VGA_AR_ENABLE_DISPLAY, 0);	
 	}
 	spin_unlock_irq(&vga_lock);
-	lock_kernel();
+	tty_lock();
 	return 0;
 }
 

include/linux/tty.h

···
 #include <linux/tty_driver.h>
 #include <linux/tty_ldisc.h>
 #include <linux/mutex.h>
+#include <linux/smp_lock.h>
 
 #include <asm/system.h>
 
···
 
 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
+	/* kernel_locked is 1 for !CONFIG_LOCK_KERNEL */
+	WARN_ON(kernel_locked());
+#endif
+	lock_kernel();
+}
+static inline void tty_unlock(void) __releases(kernel_lock)
+{
+	unlock_kernel();
+}
+#define tty_locked()		(kernel_locked())
 
 #endif /* __KERNEL__ */
 #endif