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() */