1 files changed, 54 insertions, 28 deletions

diff --git a/drivers/tty/tty_mutex.c b/drivers/tty/tty_mutex.c
index 133697540c7..2e41abebbcb 100644
--- a/drivers/tty/tty_mutex.c
+++ b/drivers/tty/tty_mutex.c
@@ -1,47 +1,73 @@
-/*
- * drivers/char/tty_lock.c
- */
 #include <linux/tty.h>
 #include <linux/module.h>
 #include <linux/kallsyms.h>
 #include <linux/semaphore.h>
 #include <linux/sched.h>
 
-/*
- * The 'big tty mutex'
- *
- * This mutex is taken and released by tty_lock() and tty_unlock(),
- * replacing the older big kernel lock.
- * It can no longer be taken recursively, and does not get
- * released implicitly while sleeping.
- *
- * Don't use in new code.
- */
-static DEFINE_MUTEX(big_tty_mutex);
-struct task_struct *__big_tty_mutex_owner;
-EXPORT_SYMBOL_GPL(__big_tty_mutex_owner);
+/* Legacy tty mutex glue */
+
+enum {
+	TTY_MUTEX_NORMAL,
+	TTY_MUTEX_NESTED,
+};
 
 /*
  * Getting the big tty mutex.
  */
-void __lockfunc tty_lock(void)
-{
-	struct task_struct *task = current;
 
-	WARN_ON(__big_tty_mutex_owner == task);
+static void __lockfunc tty_lock_nested(struct tty_struct *tty,
+				       unsigned int subclass)
+{
+	if (tty->magic != TTY_MAGIC) {
+		pr_err("L Bad %p\n", tty);
+		WARN_ON(1);
+		return;
+	}
+	tty_kref_get(tty);
+	mutex_lock_nested(&tty->legacy_mutex, subclass);
+}
 
-	mutex_lock(&big_tty_mutex);
-	__big_tty_mutex_owner = task;
+void __lockfunc tty_lock(struct tty_struct *tty)
+{
+	return tty_lock_nested(tty, TTY_MUTEX_NORMAL);
 }
 EXPORT_SYMBOL(tty_lock);
 
-void __lockfunc tty_unlock(void)
+void __lockfunc tty_unlock(struct tty_struct *tty)
 {
-	struct task_struct *task = current;
+	if (tty->magic != TTY_MAGIC) {
+		pr_err("U Bad %p\n", tty);
+		WARN_ON(1);
+		return;
+	}
+	mutex_unlock(&tty->legacy_mutex);
+	tty_kref_put(tty);
+}
+EXPORT_SYMBOL(tty_unlock);
 
-	WARN_ON(__big_tty_mutex_owner != task);
-	__big_tty_mutex_owner = NULL;
+/*
+ * Getting the big tty mutex for a pair of ttys with lock ordering
+ * On a non pty/tty pair tty2 can be NULL which is just fine.
+ */
+void __lockfunc tty_lock_pair(struct tty_struct *tty,
+					struct tty_struct *tty2)
+{
+	if (tty < tty2) {
+		tty_lock(tty);
+		tty_lock_nested(tty2, TTY_MUTEX_NESTED);
+	} else {
+		if (tty2 && tty2 != tty)
+			tty_lock(tty2);
+		tty_lock_nested(tty, TTY_MUTEX_NESTED);
+	}
+}
+EXPORT_SYMBOL(tty_lock_pair);
 
-	mutex_unlock(&big_tty_mutex);
+void __lockfunc tty_unlock_pair(struct tty_struct *tty,
+						struct tty_struct *tty2)
+{
+	tty_unlock(tty);
+	if (tty2 && tty2 != tty)
+		tty_unlock(tty2);
 }
-EXPORT_SYMBOL(tty_unlock);
+EXPORT_SYMBOL(tty_unlock_pair);