tty: Preset lock subclass for nested tty locks

Eliminate the requirement of specifying the tty lock nesting at
lock time; instead, set the lock subclass for slave ptys at pty
install (normal ttys and master ptys use subclass 0).

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

3 files changed, 12 insertions, 10 deletions

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index bdb8fd1a2026..11db7dc8676b 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -399,6 +399,8 @@ static int pty_common_install(struct tty_driver *driver, struct tty_struct *tty,
         if (!o_tty)
                 goto err_put_module;
 
+        tty_set_lock_subclass(o_tty);
+
         if (legacy) {
                 /* We always use new tty termios data so we can do this
                    the easy way .. */
diff --git a/drivers/tty/tty_mutex.c b/drivers/tty/tty_mutex.c
index f43e995c7a0f..4486741190c4 100644
--- a/drivers/tty/tty_mutex.c
+++ b/drivers/tty/tty_mutex.c
@@ -13,15 +13,14 @@
 
 enum {
         TTY_MUTEX_NORMAL,
-        TTY_MUTEX_NESTED,
+        TTY_MUTEX_SLAVE,
 };
 
 /*
  * Getting the big tty mutex.
  */
 
-static void __lockfunc tty_lock_nested(struct tty_struct *tty,
-                                       unsigned int subclass)
+void __lockfunc tty_lock(struct tty_struct *tty)
 {
         if (tty->magic != TTY_MAGIC) {
                 pr_err("L Bad %p\n", tty);
@@ -29,12 +28,7 @@ static void __lockfunc tty_lock_nested(struct tty_struct *tty,
                 return;
         }
         tty_kref_get(tty);
-        mutex_lock_nested(&tty->legacy_mutex, subclass);
-}
-
-void __lockfunc tty_lock(struct tty_struct *tty)
-{
-        return tty_lock_nested(tty, TTY_MUTEX_NORMAL);
+        mutex_lock(&tty->legacy_mutex);
 }
 EXPORT_SYMBOL(tty_lock);
 
@@ -56,7 +50,7 @@ void __lockfunc tty_lock_slave(struct tty_struct *tty)
                 WARN_ON(!mutex_is_locked(&tty->link->legacy_mutex) ||
                         !tty->driver->type == TTY_DRIVER_TYPE_PTY ||
                         !tty->driver->type == PTY_TYPE_SLAVE);
-                tty_lock_nested(tty, TTY_MUTEX_NESTED);
+                tty_lock(tty);
         }
 }
 
@@ -65,3 +59,8 @@ void __lockfunc tty_unlock_slave(struct tty_struct *tty)
         if (tty && tty != tty->link)
                 tty_unlock(tty);
 }
+
+void tty_set_lock_subclass(struct tty_struct *tty)
+{
+        lockdep_set_subclass(&tty->legacy_mutex, TTY_MUTEX_SLAVE);
+}
diff --git a/include/linux/tty.h b/include/linux/tty.h
index a07b4b415db8..196c352a5ce8 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -640,6 +640,7 @@ extern void __lockfunc tty_lock(struct tty_struct *tty);
 extern void __lockfunc tty_unlock(struct tty_struct *tty);
 extern void __lockfunc tty_lock_slave(struct tty_struct *tty);
 extern void __lockfunc tty_unlock_slave(struct tty_struct *tty);
+extern void tty_set_lock_subclass(struct tty_struct *tty);
 /*
  * this shall be called only from where BTM is held (like close)
  *