tty: Add lock/unlock ldisc pair functions

Just as the tty pair must be locked in a stable sequence
(ie, independent of which is consider the 'other' tty), so must
the ldisc pair be locked in a stable sequence as well.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 8166260aa839f20ad107477b97777e1e2c5574ee..418c9f64a9fd08ad17c4a23d8dca3768b0d0210a 100644 (file)
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -31,6 +31,13 @@
 #define tty_ldisc_debug(tty, f, args...)
 #endif
 
+/* lockdep nested classes for tty->ldisc_sem */
+enum {
+       LDISC_SEM_NORMAL,
+       LDISC_SEM_OTHER,
+};
+
+
 /*
  *     This guards the refcounted line discipline lists. The lock
  *     must be taken with irqs off because there are hangup path
@@ -351,6 +358,86 @@ void tty_ldisc_deref(struct tty_ldisc *ld)
 }
 EXPORT_SYMBOL_GPL(tty_ldisc_deref);
 
+
+static inline int __lockfunc
+tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
+{
+       return ldsem_down_write(&tty->ldisc_sem, timeout);
+}
+
+static inline int __lockfunc
+tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
+{
+       return ldsem_down_write_nested(&tty->ldisc_sem,
+                                      LDISC_SEM_OTHER, timeout);
+}
+
+static inline void tty_ldisc_unlock(struct tty_struct *tty)
+{
+       return ldsem_up_write(&tty->ldisc_sem);
+}
+
+static int __lockfunc
+tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
+                           unsigned long timeout)
+{
+       int ret;
+
+       if (tty < tty2) {
+               ret = tty_ldisc_lock(tty, timeout);
+               if (ret) {
+                       ret = tty_ldisc_lock_nested(tty2, timeout);
+                       if (!ret)
+                               tty_ldisc_unlock(tty);
+               }
+       } else {
+               /* if this is possible, it has lots of implications */
+               WARN_ON_ONCE(tty == tty2);
+               if (tty2 && tty != tty2) {
+                       ret = tty_ldisc_lock(tty2, timeout);
+                       if (ret) {
+                               ret = tty_ldisc_lock_nested(tty, timeout);
+                               if (!ret)
+                                       tty_ldisc_unlock(tty2);
+                       }
+               } else
+                       ret = tty_ldisc_lock(tty, timeout);
+       }
+
+       if (!ret)
+               return -EBUSY;
+
+       set_bit(TTY_LDISC_HALTED, &tty->flags);
+       if (tty2)
+               set_bit(TTY_LDISC_HALTED, &tty2->flags);
+       return 0;
+}
+
+static void __lockfunc
+tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
+{
+       tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
+}
+
+static void __lockfunc tty_ldisc_unlock_pair(struct tty_struct *tty,
+                                            struct tty_struct *tty2)
+{
+       tty_ldisc_unlock(tty);
+       if (tty2)
+               tty_ldisc_unlock(tty2);
+}
+
+static void __lockfunc tty_ldisc_enable_pair(struct tty_struct *tty,
+                                            struct tty_struct *tty2)
+{
+       clear_bit(TTY_LDISC_HALTED, &tty->flags);
+       if (tty2)
+               clear_bit(TTY_LDISC_HALTED, &tty2->flags);
+
+       tty_ldisc_unlock_pair(tty, tty2);
+}
+
+
 /**
  *     tty_ldisc_enable        -       allow ldisc use
  *     @tty: terminal to activate ldisc on