3 files changed, 19 insertions, 1 deletions

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index f882ac81b93a..0e273158edac 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -212,10 +212,16 @@ static int pty_signal(struct tty_struct *tty, int sig)
 static void pty_flush_buffer(struct tty_struct *tty)
 {
         struct tty_struct *to = tty->link;
+        struct tty_ldisc *ld;
 
         if (!to)
                 return;
-        /* tty_buffer_flush(to); FIXME */
+
+        ld = tty_ldisc_ref(to);
+        tty_buffer_flush(to, ld);
+        if (ld)
+                tty_ldisc_deref(ld);
+
         if (to->packet) {
                 spin_lock_irq(&tty->ctrl_lock);
                 tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
@@ -425,6 +431,8 @@ static int pty_common_install(struct tty_driver *driver, struct tty_struct *tty,
         tty->port = ports[1];
         o_tty->port->itty = o_tty;
 
+        tty_buffer_set_lock_subclass(o_tty->port);
+
         tty_driver_kref_get(driver);
         tty->count++;
         o_tty->count++;
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 3605103fc1ac..75661641f5fe 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -557,3 +557,9 @@ int tty_buffer_set_limit(struct tty_port *port, int limit)
         return 0;
 }
 EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
+
+/* slave ptys can claim nested buffer lock when handling BRK and INTR */
+void tty_buffer_set_lock_subclass(struct tty_port *port)
+{
+        lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
+}
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 849659908f23..55964b9490dd 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -25,6 +25,9 @@
  *
  * legacy_mutex - Nested tty locks are necessary for releasing pty pairs.
  *                The stable lock order is master pty first, then slave pty.
+ * tty_buffer lock - slave ptys can claim nested buffer lock when handling
+ *                   signal chars. The stable lock order is slave pty, then
+ *                   master.
  */
 
 enum {
@@ -460,6 +463,7 @@ extern void tty_flush_to_ldisc(struct tty_struct *tty);
 extern void tty_buffer_free_all(struct tty_port *port);
 extern void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld);
 extern void tty_buffer_init(struct tty_port *port);
+extern void tty_buffer_set_lock_subclass(struct tty_port *port);
 extern speed_t tty_termios_baud_rate(struct ktermios *termios);
 extern speed_t tty_termios_input_baud_rate(struct ktermios *termios);
 extern void tty_termios_encode_baud_rate(struct ktermios *termios,