tty: Make lock subclasses available for other tty locks

Besides nested legacy_mutex locking which is required on pty pair
teardown, other nested pty operations require lock subclassing.

Move lock subclass definition to tty interface header, include/linux/tty.h,
and document its use.

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

diff --git a/drivers/tty/tty_mutex.c b/drivers/tty/tty_mutex.c
index a872389dc0bcd8309c6138057c90c9c0abf1f089..0efcf713b756e5e7eaf95bf7b5f2a744fc7f6dc0 100644 (file)
--- a/drivers/tty/tty_mutex.c
+++ b/drivers/tty/tty_mutex.c
@@ -4,18 +4,8 @@
 #include <linux/semaphore.h>
 #include <linux/sched.h>
 
-/*
- * Nested tty locks are necessary for releasing pty pairs.
- * The stable lock order is master pty first, then slave pty.
- */
-
 /* Legacy tty mutex glue */
 
-enum {
-       TTY_MUTEX_NORMAL,
-       TTY_MUTEX_SLAVE,
-};
-
 /*
  * Getting the big tty mutex.
  */
@@ -58,5 +48,5 @@ void __lockfunc tty_unlock_slave(struct tty_struct *tty)
 
 void tty_set_lock_subclass(struct tty_struct *tty)
 {
-       lockdep_set_subclass(&tty->legacy_mutex, TTY_MUTEX_SLAVE);
+       lockdep_set_subclass(&tty->legacy_mutex, TTY_LOCK_SLAVE);
 }

diff --git a/include/linux/tty.h b/include/linux/tty.h
index 7d66ae508e5cc08c0ba8f91b09e55224a565f04d..849659908f23ddbd3bbf86aec2d5848d13eb8a24 100644 (file)
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -14,6 +14,23 @@
 #include <linux/llist.h>
 
 
+/*
+ * 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.
+ */
+
+enum {
+       TTY_LOCK_NORMAL = 0,
+       TTY_LOCK_SLAVE,
+};
 
 /*
  * (Note: the *_driver.minor_start values 1, 64, 128, 192 are