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 8166260..418c9f6 100644
--- 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 @@
}
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