tty: Make tty_files_lock per-tty

Access to tty->tty_files list is always per-tty, never for all ttys
simultaneously. Replace global tty_files_lock spinlock with per-tty
->files_lock. Initialize when the ->tty_files list is inited, in
alloc_tty_struct().

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index f8110cf..8010bc5 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2415,7 +2415,7 @@
 
 	tty = get_current_tty();
 	if (tty) {
-		spin_lock(&tty_files_lock);
+		spin_lock(&tty->files_lock);
 		if (!list_empty(&tty->tty_files)) {
 			struct tty_file_private *file_priv;
 
@@ -2430,7 +2430,7 @@
 			if (file_path_has_perm(cred, file, FILE__READ | FILE__WRITE))
 				drop_tty = 1;
 		}
-		spin_unlock(&tty_files_lock);
+		spin_unlock(&tty->files_lock);
 		tty_kref_put(tty);
 	}
 	/* Reset controlling tty. */