tty: add lockdep annotations

tty_lock_pair() do the right thing to avoid deadlocks, but should
instruct LOCKDEP of this to avoid a splat.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 4 deletions

diff --git a/drivers/tty/tty_mutex.c b/drivers/tty/tty_mutex.c
index 69adc80c98cd..67feac9e6ebb 100644
--- a/drivers/tty/tty_mutex.c
+++ b/drivers/tty/tty_mutex.c
@@ -6,11 +6,17 @@
 
 /* Legacy tty mutex glue */
 
+enum {
+        TTY_MUTEX_NORMAL,
+        TTY_MUTEX_NESTED,
+};
+
 /*
  * Getting the big tty mutex.
  */
 
-void __lockfunc tty_lock(struct tty_struct *tty)
+static void __lockfunc tty_lock_nested(struct tty_struct *tty,
+                                       unsigned int subclass)
 {
         if (tty->magic != TTY_MAGIC) {
                 printk(KERN_ERR "L Bad %p\n", tty);
@@ -18,7 +24,12 @@ void __lockfunc tty_lock(struct tty_struct *tty)
                 return;
         }
         tty_kref_get(tty);
-        mutex_lock(&tty->legacy_mutex);
+        mutex_lock_nested(&tty->legacy_mutex, subclass);
+}
+
+void __lockfunc tty_lock(struct tty_struct *tty)
+{
+        return tty_lock_nested(tty, TTY_MUTEX_NORMAL);
 }
 EXPORT_SYMBOL(tty_lock);
 
@@ -43,11 +54,11 @@ void __lockfunc tty_lock_pair(struct tty_struct *tty,
 {
         if (tty < tty2) {
                 tty_lock(tty);
-                tty_lock(tty2);
+                tty_lock_nested(tty2, TTY_MUTEX_NESTED);
         } else {
                 if (tty2 && tty2 != tty)
                         tty_lock(tty2);
-                tty_lock(tty);
+                tty_lock_nested(tty, TTY_MUTEX_NESTED);
         }
 }
 EXPORT_SYMBOL(tty_lock_pair);