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, 3 insertions, 0 deletions

diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index 706ff34728f1..6288356b769d 100644
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -181,6 +181,7 @@ static int pty_set_lock(struct tty_struct *tty, int __user * arg)
 static void pty_flush_buffer(struct tty_struct *tty)
 {
         struct tty_struct *to = tty->link;
+        unsigned long flags;
         
         if (!to)
                 return;
@@ -189,8 +190,10 @@ static void pty_flush_buffer(struct tty_struct *tty)
                 to->ldisc.flush_buffer(to);
         
         if (to->packet) {
+                spin_lock_irqsave(&tty->ctrl_lock, flags);
                 tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
                 wake_up_interruptible(&to->read_wait);
+                spin_unlock_irqrestore(&tty->ctrl_lock, flags);
         }
 }