tty: BKL pushdown

- Push the BKL down into the line disciplines
- Switch the tty layer to unlocked_ioctl
- Introduce a new ctrl_lock spin lock for the control bits
- Eliminate much of the lock_kernel use in n_tty
- Prepare to (but don't yet) call the drivers with the lock dropped
  on the paths that historically held the lock

BKL now primarily protects open/close/ldisc change in the tty layer

[jirislaby@gmail.com: a couple of fixes]
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 6 deletions

diff --git a/drivers/char/n_hdlc.c b/drivers/char/n_hdlc.c
index 06803ed5568c..a07c0af4819e 100644
--- a/drivers/char/n_hdlc.c
+++ b/drivers/char/n_hdlc.c
@@ -578,26 +578,36 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
                 return -EFAULT;
         }
 
+        lock_kernel();
+
         for (;;) {
-                if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
+                if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
+                        unlock_kernel();
                         return -EIO;
+                }
 
                 n_hdlc = tty2n_hdlc (tty);
                 if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC ||
-                         tty != n_hdlc->tty)
+                         tty != n_hdlc->tty) {
+                        unlock_kernel();
                         return 0;
+                }
 
                 rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
                 if (rbuf)
                         break;
                         
                 /* no data */
-                if (file->f_flags & O_NONBLOCK)
+                if (file->f_flags & O_NONBLOCK) {
+                        unlock_kernel();
                         return -EAGAIN;
+                }
                         
                 interruptible_sleep_on (&tty->read_wait);
-                if (signal_pending(current))
+                if (signal_pending(current)) {
+                        unlock_kernel();
                         return -EINTR;
+                }
         }
                 
         if (rbuf->count > nr)
@@ -618,7 +628,7 @@ 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();
         return ret;
         
 }       /* end of n_hdlc_tty_read() */
@@ -661,6 +671,8 @@ static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
                 count = maxframe;
         }
         
+        lock_kernel();
+
         add_wait_queue(&tty->write_wait, &wait);
         set_current_state(TASK_INTERRUPTIBLE);
         
@@ -695,7 +707,7 @@ 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();
         return error;
         
 }       /* end of n_hdlc_tty_write() */