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, 6 insertions, 0 deletions

diff --git a/drivers/char/tty_ioctl.c b/drivers/char/tty_ioctl.c
index f95a80b2265f..d6353d89b451 100644
--- a/drivers/char/tty_ioctl.c
+++ b/drivers/char/tty_ioctl.c
@@ -395,6 +395,7 @@ static void change_termios(struct tty_struct *tty, struct ktermios *new_termios)
         int canon_change;
         struct ktermios old_termios = *tty->termios;
         struct tty_ldisc *ld;
+        unsigned long flags;
 
         /*
          *      Perform the actual termios internal changes under lock.
@@ -429,11 +430,13 @@ static void change_termios(struct tty_struct *tty, struct ktermios *new_termios)
                                 STOP_CHAR(tty) == '\023' &&
                                 START_CHAR(tty) == '\021');
                 if (old_flow != new_flow) {
+                        spin_lock_irqsave(&tty->ctrl_lock, flags);
                         tty->ctrl_status &= ~(TIOCPKT_DOSTOP | TIOCPKT_NOSTOP);
                         if (new_flow)
                                 tty->ctrl_status |= TIOCPKT_DOSTOP;
                         else
                                 tty->ctrl_status |= TIOCPKT_NOSTOP;
+                        spin_unlock_irqrestore(&tty->ctrl_lock, flags);
                         wake_up_interruptible(&tty->link->read_wait);
                 }
         }
@@ -905,6 +908,7 @@ int n_tty_ioctl(struct tty_struct *tty, struct file *file,
                        unsigned int cmd, unsigned long arg)
 {
         struct tty_struct *real_tty;
+        unsigned long flags;
         int retval;
 
         if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
@@ -963,6 +967,7 @@ int n_tty_ioctl(struct tty_struct *tty, struct file *file,
                         return -ENOTTY;
                 if (get_user(pktmode, (int __user *) arg))
                         return -EFAULT;
+                spin_lock_irqsave(&tty->ctrl_lock, flags);
                 if (pktmode) {
                         if (!tty->packet) {
                                 tty->packet = 1;
@@ -970,6 +975,7 @@ int n_tty_ioctl(struct tty_struct *tty, struct file *file,
                         }
                 } else
                         tty->packet = 0;
+                spin_unlock_irqrestore(&tty->ctrl_lock, flags);
                 return 0;
         }
         default: