1 files changed, 44 insertions, 0 deletions

diff --git a/drivers/tty/tty_mutex.c b/drivers/tty/tty_mutex.c
new file mode 100644
index 000000000000..3b2bb7719442
--- /dev/null
+++ b/drivers/tty/tty_mutex.c
@@ -0,0 +1,44 @@
+#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);
+
+/*
+ * Getting the big tty mutex.
+ */
+void __lockfunc tty_lock(void)
+{
+        struct task_struct *task = current;
+
+        WARN_ON(__big_tty_mutex_owner == task);
+
+        mutex_lock(&big_tty_mutex);
+        __big_tty_mutex_owner = task;
+}
+EXPORT_SYMBOL(tty_lock);
+
+void __lockfunc tty_unlock(void)
+{
+        struct task_struct *task = current;
+
+        WARN_ON(__big_tty_mutex_owner != task);
+        __big_tty_mutex_owner = NULL;
+
+        mutex_unlock(&big_tty_mutex);
+}
+EXPORT_SYMBOL(tty_unlock);