3 files changed, 34 insertions, 15 deletions

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 5793aa0d3bfb..cf6e0f2e1331 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -1090,16 +1090,45 @@ static void eraser(unsigned char c, struct tty_struct *tty)
  *      Called when a signal is being sent due to terminal input.
  *      Called from the driver receive_buf path so serialized.
  *
+ *      Performs input and output flush if !NOFLSH. In this context, the echo
+ *      buffer is 'output'. The signal is processed first to alert any current
+ *      readers or writers to discontinue and exit their i/o loops.
+ *
  *      Locking: ctrl_lock
  */
 
 static void isig(int sig, struct tty_struct *tty)
 {
+        struct n_tty_data *ldata = tty->disc_data;
         struct pid *tty_pgrp = tty_get_pgrp(tty);
         if (tty_pgrp) {
                 kill_pgrp(tty_pgrp, sig, 1);
                 put_pid(tty_pgrp);
         }
+
+        if (!L_NOFLSH(tty)) {
+                up_read(&tty->termios_rwsem);
+                down_write(&tty->termios_rwsem);
+
+                /* clear echo buffer */
+                mutex_lock(&ldata->output_lock);
+                ldata->echo_head = ldata->echo_tail = 0;
+                ldata->echo_mark = ldata->echo_commit = 0;
+                mutex_unlock(&ldata->output_lock);
+
+                /* clear output buffer */
+                tty_driver_flush_buffer(tty);
+
+                /* clear input buffer */
+                reset_buffer_flags(tty->disc_data);
+
+                /* notify pty master of flush */
+                if (tty->link)
+                        n_tty_packet_mode_flush(tty);
+
+                up_write(&tty->termios_rwsem);
+                down_read(&tty->termios_rwsem);
+        }
 }
 
 /**
@@ -1123,13 +1152,6 @@ static void n_tty_receive_break(struct tty_struct *tty)
                 return;
         if (I_BRKINT(tty)) {
                 isig(SIGINT, tty);
-                if (!L_NOFLSH(tty)) {
-                        /* flushing needs exclusive termios_rwsem */
-                        up_read(&tty->termios_rwsem);
-                        n_tty_flush_buffer(tty);
-                        tty_driver_flush_buffer(tty);
-                        down_read(&tty->termios_rwsem);
-                }
                 return;
         }
         if (I_PARMRK(tty)) {
@@ -1203,13 +1225,7 @@ static void n_tty_receive_parity_error(struct tty_struct *tty, unsigned char c)
 static void
 n_tty_receive_signal_char(struct tty_struct *tty, int signal, unsigned char c)
 {
-        if (!L_NOFLSH(tty)) {
-                /* flushing needs exclusive termios_rwsem */
-                up_read(&tty->termios_rwsem);
-                n_tty_flush_buffer(tty);
-                tty_driver_flush_buffer(tty);
-                down_read(&tty->termios_rwsem);
-        }
+        isig(signal, tty);
         if (I_IXON(tty))
                 start_tty(tty);
         if (L_ECHO(tty)) {
@@ -1217,7 +1233,6 @@ n_tty_receive_signal_char(struct tty_struct *tty, int signal, unsigned char c)
                 commit_echoes(tty);
         } else
                 process_echoes(tty);
-        isig(signal, tty);
         return;
 }
 
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 0e273158edac..e72ee629cead 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -395,6 +395,7 @@ static int pty_common_install(struct tty_driver *driver, struct tty_struct *tty,
                 goto err_put_module;
 
         tty_set_lock_subclass(o_tty);
+        lockdep_set_subclass(&o_tty->termios_rwsem, TTY_LOCK_SLAVE);
 
         if (legacy) {
                 /* We always use new tty termios data so we can do this
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 55964b9490dd..fe5623c9af71 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.
+ * termios_rwsem - The stable lock order is tty_buffer lock->termios_rwsem.
+ *                 Subclassing this lock enables the slave pty to hold its
+ *                 termios_rwsem when claiming the master tty_buffer lock.
  * tty_buffer lock - slave ptys can claim nested buffer lock when handling
  *                   signal chars. The stable lock order is slave pty, then
  *                   master.