1 files changed, 26 insertions, 0 deletions
diff --git a/drivers/tty/tty.h b/drivers/tty/tty.h
index 55003840cd68..af997a4174c5 100644
--- a/drivers/tty/tty.h
+++ b/drivers/tty/tty.h
@@ -17,6 +17,32 @@
 #define tty_info_ratelimited(tty, f, ...) \
 		tty_msg(pr_info_ratelimited, tty, f, ##__VA_ARGS__)
 
+/*
+ * Lock subclasses for tty locks
+ *
+ * TTY_LOCK_NORMAL is for normal ttys and master ptys.
+ * TTY_LOCK_SLAVE is for slave ptys only.
+ *
+ * Lock subclasses are necessary for handling nested locking with pty pairs.
+ * tty locks which use nested locking:
+ *
+ * legacy_mutex - Nested tty locks are necessary for releasing pty pairs.
+ *		  The stable lock order is master pty first, then slave pty.
+ * termios_rwsem - The stable lock order is tty_buffer lock->termios_rwsem.
+ *		   Subclassing this lock enables the slave pty to hold its
+ *		   termios_rwsem when claiming the master tty_buffer lock.
+ * tty_buffer lock - slave ptys can claim nested buffer lock when handling
+ *		     signal chars. The stable lock order is slave pty, then
+ *		     master.
+ */
+enum {
+	TTY_LOCK_NORMAL = 0,
+	TTY_LOCK_SLAVE,
+};
+
+int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout);
+void tty_ldisc_unlock(struct tty_struct *tty);
+
 /* tty_audit.c */
 #ifdef CONFIG_AUDIT
 void tty_audit_add_data(struct tty_struct *tty, const void *data, size_t size);