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>

17 files changed, 161 insertions, 115 deletions

diff --git a/drivers/char/amiserial.c b/drivers/char/amiserial.c
index 4f8d60c25a98..1b21a7adeb58 100644
--- a/drivers/char/amiserial.c
+++ b/drivers/char/amiserial.c
@@ -1072,7 +1072,7 @@ static int get_serial_info(struct async_struct * info,
         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;
@@ -1083,7 +1083,7 @@ static int get_serial_info(struct async_struct * info,
         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;
@@ -1100,14 +1100,14 @@ static int set_serial_info(struct async_struct * info,
         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;
         }
   
@@ -1127,7 +1127,7 @@ static int set_serial_info(struct async_struct * info,
         }
 
         if (new_serial.baud_base < 9600) {
-                unlock_kernel();
+                tty_unlock();
                 return -EINVAL;
         }
 
@@ -1163,7 +1163,7 @@ check_and_exit:
                 }
         } else
                 retval = startup(info);
-        unlock_kernel();
+        tty_unlock();
         return retval;
 }
 
@@ -1538,7 +1538,7 @@ static void rs_wait_until_sent(struct tty_struct *tty, int timeout)
 
         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
@@ -1579,7 +1579,7 @@ static void rs_wait_until_sent(struct tty_struct *tty, int timeout)
                         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
diff --git a/drivers/char/briq_panel.c b/drivers/char/briq_panel.c
index 555cd93c2ee5..d5fa113afe37 100644
--- a/drivers/char/briq_panel.c
+++ b/drivers/char/briq_panel.c
@@ -67,15 +67,15 @@ static void set_led(char state)
 
 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;
 }
 
diff --git a/drivers/char/n_hdlc.c b/drivers/char/n_hdlc.c
index c68118efad84..47d32281032c 100644
--- a/drivers/char/n_hdlc.c
+++ b/drivers/char/n_hdlc.c
@@ -598,18 +598,18 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
                 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;
                 }
 
@@ -619,13 +619,13 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
                         
                 /* 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;
                 }
         }
@@ -648,7 +648,7 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
                 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() */
@@ -691,7 +691,7 @@ static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
                 count = maxframe;
         }
         
-        lock_kernel();
+        tty_lock();
 
         add_wait_queue(&tty->write_wait, &wait);
         set_current_state(TASK_INTERRUPTIBLE);
@@ -731,7 +731,7 @@ static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
                 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() */
diff --git a/drivers/char/n_r3964.c b/drivers/char/n_r3964.c
index c1d8b54c816d..f4bd2591e39f 100644
--- a/drivers/char/n_r3964.c
+++ b/drivers/char/n_r3964.c
@@ -1067,7 +1067,7 @@ static ssize_t r3964_read(struct tty_struct *tty, struct file *file,
 
         TRACE_L("read()");
 
-        lock_kernel();
+        tty_lock();
 
         pClient = findClient(pInfo, task_pid(current));
         if (pClient) {
@@ -1109,7 +1109,7 @@ static ssize_t r3964_read(struct tty_struct *tty, struct file *file,
         }
         ret = -EPERM;
 unlock:
-        unlock_kernel();
+        tty_unlock();
         return ret;
 }
 
@@ -1158,7 +1158,7 @@ static ssize_t r3964_write(struct tty_struct *tty, struct file *file,
         pHeader->locks = 0;
         pHeader->owner = NULL;
 
-        lock_kernel();
+        tty_lock();
 
         pClient = findClient(pInfo, task_pid(current));
         if (pClient) {
@@ -1177,7 +1177,7 @@ static ssize_t r3964_write(struct tty_struct *tty, struct file *file,
         add_tx_queue(pInfo, pHeader);
         trigger_transmit(pInfo);
 
-        unlock_kernel();
+        tty_unlock();
 
         return 0;
 }
diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index b640ef29be1c..622e21ca9a5c 100644
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -692,9 +692,9 @@ static int ptmx_open(struct inode *inode, struct file *filp)
 {
         int ret;
 
-        lock_kernel();
+        tty_lock();
         ret = __ptmx_open(inode, filp);
-        unlock_kernel();
+        tty_unlock();
         return ret;
 }
 
diff --git a/drivers/char/selection.c b/drivers/char/selection.c
index 6e79340d732f..85211a3a5811 100644
--- a/drivers/char/selection.c
+++ b/drivers/char/selection.c
@@ -313,7 +313,7 @@ int paste_selection(struct tty_struct *tty)
         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();
@@ -338,6 +338,6 @@ int paste_selection(struct tty_struct *tty)
         __set_current_state(TASK_RUNNING);
 
         tty_ldisc_deref(ld);
-        unlock_kernel();
+        tty_unlock();
         return 0;
 }
diff --git a/drivers/char/serial167.c b/drivers/char/serial167.c
index ecbe479c7d68..90b3ec0aabdd 100644
--- a/drivers/char/serial167.c
+++ b/drivers/char/serial167.c
@@ -1505,7 +1505,7 @@ cy_ioctl(struct tty_struct *tty, struct file *file,
         printk("cy_ioctl %s, cmd = %x arg = %lx\n", tty->name, cmd, arg);       /* */
 #endif
 
-        lock_kernel();
+        tty_lock();
 
         switch (cmd) {
         case CYGETMON:
@@ -1561,7 +1561,7 @@ cy_ioctl(struct tty_struct *tty, struct file *file,
         default:
                 ret_val = -ENOIOCTLCMD;
         }
-        unlock_kernel();
+        tty_unlock();
 
 #ifdef SERIAL_DEBUG_OTHER
         printk("cy_ioctl done\n");
diff --git a/drivers/char/sx.c b/drivers/char/sx.c
index a81ec4fcf6ff..5b24db4ff7f1 100644
--- a/drivers/char/sx.c
+++ b/drivers/char/sx.c
@@ -1699,7 +1699,7 @@ static long sx_fw_ioctl(struct file *filp, unsigned int cmd,
         if (!capable(CAP_SYS_RAWIO))
                 return -EPERM;
 
-        lock_kernel();
+        tty_lock();
 
         sx_dprintk(SX_DEBUG_FIRMWARE, "IOCTL %x: %lx\n", cmd, arg);
 
@@ -1848,7 +1848,7 @@ static long sx_fw_ioctl(struct file *filp, unsigned int cmd,
                 break;
         }
 out:
-        unlock_kernel();
+        tty_unlock();
         func_exit();
         return rc;
 }
@@ -1859,7 +1859,7 @@ static int sx_break(struct tty_struct *tty, int flag)
         int rv;
 
         func_enter();
-        lock_kernel();
+        tty_lock();
 
         if (flag)
                 rv = sx_send_command(port, HS_START, -1, HS_IDLE_BREAK);
@@ -1868,7 +1868,7 @@ static int sx_break(struct tty_struct *tty, int flag)
         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;
 }
@@ -1909,7 +1909,7 @@ static int sx_ioctl(struct tty_struct *tty, struct file *filp,
         /* func_enter2(); */
 
         rc = 0;
-        lock_kernel();
+        tty_lock();
         switch (cmd) {
         case TIOCGSERIAL:
                 rc = gs_getserial(&port->gs, argp);
@@ -1921,7 +1921,7 @@ static int sx_ioctl(struct tty_struct *tty, struct file *filp,
                 rc = -ENOIOCTLCMD;
                 break;
         }
-        unlock_kernel();
+        tty_unlock();
 
         /* func_exit(); */
         return rc;
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;
 }
 
diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
index 500e740ec5e4..97681ffd6cbd 100644
--- a/drivers/char/tty_ldisc.c
+++ b/drivers/char/tty_ldisc.c
@@ -440,6 +440,8 @@ static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
  *
  *      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)
@@ -447,10 +449,10 @@ 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;
@@ -553,7 +555,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
         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.
@@ -567,12 +569,12 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
          */
 
         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
@@ -594,7 +596,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
                 mutex_lock(&tty->ldisc_mutex);
         }
 
-        lock_kernel();
+        tty_lock();
 
         set_bit(TTY_LDISC_CHANGING, &tty->flags);
 
@@ -607,7 +609,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
         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
@@ -633,14 +635,14 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
         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;
         }
 
@@ -682,7 +684,7 @@ 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();
+        tty_unlock();
         return retval;
 }
 
diff --git a/drivers/char/vc_screen.c b/drivers/char/vc_screen.c
index c1791a63d99d..bcce46c96b88 100644
--- a/drivers/char/vc_screen.c
+++ b/drivers/char/vc_screen.c
@@ -463,10 +463,10 @@ vcs_open(struct inode *inode, struct file *filp)
         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;
 }
 
diff --git a/drivers/char/vt_ioctl.c b/drivers/char/vt_ioctl.c
index 72dcfb2dc126..cf87c5336229 100644
--- a/drivers/char/vt_ioctl.c
+++ b/drivers/char/vt_ioctl.c
@@ -509,7 +509,7 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 
         console = vc->vc_num;
 
-        lock_kernel();
+        tty_lock();
 
         if (!vc_cons_allocated(console)) {      /* impossible? */
                 ret = -ENOIOCTLCMD;
@@ -1336,7 +1336,7 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
                 ret = -ENOIOCTLCMD;
         }
 out:
-        unlock_kernel();
+        tty_unlock();
         return ret;
 eperm:
         ret = -EPERM;
@@ -1503,7 +1503,7 @@ long vt_compat_ioctl(struct tty_struct *tty, struct file * file,
 
         console = vc->vc_num;
 
-        lock_kernel();
+        tty_lock();
 
         if (!vc_cons_allocated(console)) {      /* impossible? */
                 ret = -ENOIOCTLCMD;
@@ -1571,11 +1571,11 @@ long vt_compat_ioctl(struct tty_struct *tty, struct file * file,
                 goto fallback;
         }
 out:
-        unlock_kernel();
+        tty_unlock();
         return ret;
 
 fallback:
-        unlock_kernel();
+        tty_unlock();
         return vt_ioctl(tty, file, cmd, arg);
 }
 
diff --git a/drivers/serial/68360serial.c b/drivers/serial/68360serial.c
index 768612f8e41e..16f5f2fab032 100644
--- a/drivers/serial/68360serial.c
+++ b/drivers/serial/68360serial.c
@@ -1705,7 +1705,7 @@ static void rs_360_wait_until_sent(struct tty_struct *tty, int timeout)
         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
@@ -1734,7 +1734,7 @@ static void rs_360_wait_until_sent(struct tty_struct *tty, int timeout)
                         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
diff --git a/drivers/serial/crisv10.c b/drivers/serial/crisv10.c
index 30626440a062..f848e188deae 100644
--- a/drivers/serial/crisv10.c
+++ b/drivers/serial/crisv10.c
@@ -3935,7 +3935,7 @@ static void rs_wait_until_sent(struct tty_struct *tty, int timeout)
          * 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 */
@@ -3952,7 +3952,7 @@ static void rs_wait_until_sent(struct tty_struct *tty, int timeout)
                         curr_time_usec - info->last_tx_active_usec;
         }
         set_current_state(TASK_RUNNING);
-        unlock_kernel();
+        tty_unlock();
 }
 
 /*
diff --git a/drivers/serial/serial_core.c b/drivers/serial/serial_core.c
index 3d2acc2265f7..851d7c29132b 100644
--- a/drivers/serial/serial_core.c
+++ b/drivers/serial/serial_core.c
@@ -1274,7 +1274,7 @@ static void uart_close(struct tty_struct *tty, struct file *filp)
         struct uart_port *uport;
         unsigned long flags;
 
-        BUG_ON(!kernel_locked());
+        BUG_ON(!tty_locked());
 
         if (!state)
                 return;
@@ -1382,7 +1382,7 @@ static void uart_wait_until_sent(struct tty_struct *tty, int timeout)
         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
@@ -1429,7 +1429,7 @@ static void uart_wait_until_sent(struct tty_struct *tty, int timeout)
                         break;
         }
         set_current_state(TASK_RUNNING); /* might not be needed */
-        unlock_kernel();
+        tty_unlock();
 }
 
 /*
@@ -1444,7 +1444,7 @@ static void uart_hangup(struct tty_struct *tty)
         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);
@@ -1578,7 +1578,7 @@ static int uart_open(struct tty_struct *tty, struct file *filp)
         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);
 
         /*
diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
index 182dd6f8aadd..71970057c118 100644
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c
@@ -1108,7 +1108,7 @@ static int vgacon_do_font_op(struct vgastate *state,char *arg,int set,int ch512)
                 charmap += 4 * cmapsz;
 #endif
 
-        unlock_kernel();
+        tty_unlock();
         spin_lock_irq(&vga_lock);
         /* First, the Sequencer */
         vga_wseq(state->vgabase, VGA_SEQ_RESET, 0x1);
@@ -1192,7 +1192,7 @@ static int vgacon_do_font_op(struct vgastate *state,char *arg,int set,int ch512)
                 vga_wattr(state->vgabase, VGA_AR_ENABLE_DISPLAY, 0);    
         }
         spin_unlock_irq(&vga_lock);
-        lock_kernel();
+        tty_lock();
         return 0;
 }
 
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 2df60e4ff40e..6ead6b60c743 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -13,6 +13,7 @@
 #include <linux/tty_driver.h>
 #include <linux/tty_ldisc.h>
 #include <linux/mutex.h>
+#include <linux/smp_lock.h>
 
 #include <asm/system.h>
 
@@ -576,5 +577,35 @@ extern int vt_ioctl(struct tty_struct *tty, struct file *file,
 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