pty: Fix lock inversion

[~andy/linux] / drivers / tty / tty_mutex.c

diff --git a/drivers/tty/tty_mutex.c b/drivers/tty/tty_mutex.c
index 9ff986c32a21ef702edf515a79c19440a504b747..69adc80c98cd5c035fa0f3a18df6fc3e3c127623 100644 (file)
--- a/drivers/tty/tty_mutex.c
+++ b/drivers/tty/tty_mutex.c
@@ -4,29 +4,59 @@
 #include <linux/semaphore.h>
 #include <linux/sched.h>
 
-/*
- * The 'big tty mutex'
- *
- * This mutex is taken and released by tty_lock() and tty_unlock(),
- * replacing the older big kernel lock.
- * It can no longer be taken recursively, and does not get
- * released implicitly while sleeping.
- *
- * Don't use in new code.
- */
-static DEFINE_MUTEX(big_tty_mutex);
+/* Legacy tty mutex glue */
 
 /*
  * Getting the big tty mutex.
  */
-void __lockfunc tty_lock(void)
+
+void __lockfunc tty_lock(struct tty_struct *tty)
 {
-       mutex_lock(&big_tty_mutex);
+       if (tty->magic != TTY_MAGIC) {
+               printk(KERN_ERR "L Bad %p\n", tty);
+               WARN_ON(1);
+               return;
+       }
+       tty_kref_get(tty);
+       mutex_lock(&tty->legacy_mutex);
 }
 EXPORT_SYMBOL(tty_lock);
 
-void __lockfunc tty_unlock(void)
+void __lockfunc tty_unlock(struct tty_struct *tty)
 {
-       mutex_unlock(&big_tty_mutex);
+       if (tty->magic != TTY_MAGIC) {
+               printk(KERN_ERR "U Bad %p\n", tty);
+               WARN_ON(1);
+               return;
+       }
+       mutex_unlock(&tty->legacy_mutex);
+       tty_kref_put(tty);
 }
 EXPORT_SYMBOL(tty_unlock);
+
+/*
+ * Getting the big tty mutex for a pair of ttys with lock ordering
+ * On a non pty/tty pair tty2 can be NULL which is just fine.
+ */
+void __lockfunc tty_lock_pair(struct tty_struct *tty,
+                                       struct tty_struct *tty2)
+{
+       if (tty < tty2) {
+               tty_lock(tty);
+               tty_lock(tty2);
+       } else {
+               if (tty2 && tty2 != tty)
+                       tty_lock(tty2);
+               tty_lock(tty);
+       }
+}
+EXPORT_SYMBOL(tty_lock_pair);
+
+void __lockfunc tty_unlock_pair(struct tty_struct *tty,
+                                               struct tty_struct *tty2)
+{
+       tty_unlock(tty);
+       if (tty2 && tty2 != tty)
+               tty_unlock(tty2);
+}
+EXPORT_SYMBOL(tty_unlock_pair);