3 files changed, 53 insertions, 13 deletions

diff --git a/drivers/char/Makefile b/drivers/char/Makefile
index 273cee1cc77b..dc9641660605 100644
--- a/drivers/char/Makefile
+++ b/drivers/char/Makefile
@@ -9,6 +9,7 @@ FONTMAPFILE = cp437.uni
 
 obj-y    += mem.o random.o tty_io.o n_tty.o tty_ioctl.o tty_ldisc.o tty_buffer.o tty_port.o
 
+obj-y                           += tty_mutex.o
 obj-$(CONFIG_LEGACY_PTYS)       += pty.o
 obj-$(CONFIG_UNIX98_PTYS)       += pty.o
 obj-y                           += misc.o
diff --git a/drivers/char/tty_mutex.c b/drivers/char/tty_mutex.c
new file mode 100644
index 000000000000..133697540c73
--- /dev/null
+++ b/drivers/char/tty_mutex.c
@@ -0,0 +1,47 @@
+/*
+ * 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);
+
+/*
+ * 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);
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 0fbafb0b69bf..1437da3ddc62 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -578,20 +578,12 @@ extern int vt_ioctl(struct tty_struct *tty, struct file *file,
 extern long vt_compat_ioctl(struct tty_struct *tty, struct file * file,
                      unsigned int cmd, unsigned long arg);
 
+/* tty_mutex.c */
 /* functions for preparation of BKL removal */
-static inline void tty_lock(void) __acquires(kernel_lock)
-{
-#ifdef CONFIG_LOCK_KERNEL
-        /* kernel_locked is 1 for !CONFIG_LOCK_KERNEL */
-        WARN_ON(kernel_locked());
-#endif
-        lock_kernel();
-}
-static inline void tty_unlock(void) __releases(kernel_lock)
-{
-        unlock_kernel();
-}
-#define tty_locked()            (kernel_locked())
+extern void __lockfunc tty_lock(void) __acquires(tty_lock);
+extern void __lockfunc tty_unlock(void) __releases(tty_lock);
+extern struct task_struct *__big_tty_mutex_owner;
+#define tty_locked()            (current == __big_tty_mutex_owner)
 
 /*
  * wait_event_interruptible_tty -- wait for a condition with the tty lock held