tty: Refactor tty_ldisc_reinit() for reuse

At tty hangup, the line discipline instance is reinitialized by
closing the current ldisc instance and opening a new instance.
This operation is complicated by error recovery: if the attempt
to reinit the current line discipline fails, the line discipline
is reset to N_TTY (which should not but can fail).

Re-purpose tty_ldisc_reinit() to return a valid, open line discipline
instance, or otherwise, an error.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 45aa31b923e524ab696e50c606242e5a23ae3ce5..e18c8e86411040e5fe452abe9790b03aba5d3b18 100644 (file)
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -641,26 +641,41 @@ static void tty_reset_termios(struct tty_struct *tty)
  *     @tty: tty to reinit
  *     @disc: line discipline to reinitialize
  *
- *     Switch the tty to a line discipline and leave the ldisc
- *     state closed
+ *     Completely reinitialize the line discipline state, by closing the
+ *     current instance and opening a new instance. If an error occurs opening
+ *     the new non-N_TTY instance, the instance is dropped and tty->ldisc reset
+ *     to NULL. The caller can then retry with N_TTY instead.
+ *
+ *     Returns 0 if successful, otherwise error code < 0
  */
 
 static int tty_ldisc_reinit(struct tty_struct *tty, int disc)
 {
-       struct tty_ldisc *ld = tty_ldisc_get(tty, disc);
+       struct tty_ldisc *ld;
+       int retval;
 
-       if (IS_ERR(ld))
-               return -1;
+       ld = tty_ldisc_get(tty, disc);
+       if (IS_ERR(ld)) {
+               BUG_ON(disc == N_TTY);
+               return PTR_ERR(ld);
+       }
 
-       tty_ldisc_close(tty, tty->ldisc);
-       tty_ldisc_put(tty->ldisc);
-       /*
-        *      Switch the line discipline back
-        */
+       if (tty->ldisc) {
+               tty_ldisc_close(tty, tty->ldisc);
+               tty_ldisc_put(tty->ldisc);
+       }
+
+       /* switch the line discipline */
        tty->ldisc = ld;
        tty_set_termios_ldisc(tty, disc);
-
-       return 0;
+       retval = tty_ldisc_open(tty, tty->ldisc);
+       if (retval) {
+               if (!WARN_ON(disc == N_TTY)) {
+                       tty_ldisc_put(tty->ldisc);
+                       tty->ldisc = NULL;
+               }
+       }
+       return retval;
 }
 
 /**
@@ -716,19 +731,13 @@ void tty_ldisc_hangup(struct tty_struct *tty)
                   reopen a new ldisc. We could defer the reopen to the next
                   open but it means auditing a lot of other paths so this is
                   a FIXME */
-               if (reset == 0) {
+               if (reset == 0)
+                       err = tty_ldisc_reinit(tty, tty->termios.c_line);
 
-                       if (!tty_ldisc_reinit(tty, tty->termios.c_line))
-                               err = tty_ldisc_open(tty, tty->ldisc);
-                       else
-                               err = 1;
-               }
                /* If the re-open fails or we reset then go to N_TTY. The
                   N_TTY open cannot fail */
-               if (reset || err) {
-                       BUG_ON(tty_ldisc_reinit(tty, N_TTY));
-                       WARN_ON(tty_ldisc_open(tty, tty->ldisc));
-               }
+               if (reset || err < 0)
+                       tty_ldisc_reinit(tty, N_TTY);
        }
        tty_ldisc_unlock(tty);
        if (reset)