[PATCH -next v2 19/26] tty: Preset lock subclass for nested tty locks

[Peter Hurley]

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 <pe...@hurleysoftware.com>
---
 drivers/tty/pty.c       |  2 ++
 drivers/tty/tty_mutex.c | 19 +++++++++----------
 include/linux/tty.h     |  1 +
 3 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index bdb8fd1..11db7dc 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 f43e995..4486741 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 a07b4b4..196c352 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)
  *
-- 
2.1.3

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