tty: Add diagnostic for halted line discipline

Flip buffer work must not be scheduled by the line discipline
after the line discipline has been halted; issue warning.

Note: drivers can still schedule flip buffer work.

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

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 68865d9..16793ec 100644 (file)
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -153,6 +153,12 @@ static void n_tty_set_room(struct tty_struct *tty)
        if (left && !old_left) {
                WARN_RATELIMIT(tty->port->itty == NULL,
                                "scheduling with invalid itty\n");
+               /* see if ldisc has been killed - if so, this means that
+                * even though the ldisc has been halted and ->buf.work
+                * cancelled, ->buf.work is about to be rescheduled
+                */
+               WARN_RATELIMIT(test_bit(TTY_LDISC_HALTED, &tty->flags),
+                              "scheduling buffer work for halted ldisc\n");
                schedule_work(&tty->port->buf.work);
        }
 }
@@ -1624,6 +1630,8 @@ static int n_tty_open(struct tty_struct *tty)
                goto err_free_bufs;
 
        tty->disc_data = ldata;
+       /* indicate buffer work may resume */
+       clear_bit(TTY_LDISC_HALTED, &tty->flags);
        reset_buffer_flags(tty);
        tty_unthrottle(tty);
        ldata->column = 0;

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index d794087..c641321 100644 (file)
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -375,6 +375,7 @@ static inline void tty_ldisc_put(struct tty_ldisc *ld)
 
 void tty_ldisc_enable(struct tty_struct *tty)
 {
+       clear_bit(TTY_LDISC_HALTED, &tty->flags);
        set_bit(TTY_LDISC, &tty->flags);
        clear_bit(TTY_LDISC_CHANGING, &tty->flags);
        wake_up(&tty_ldisc_wait);
@@ -513,8 +514,11 @@ static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
 
 static int tty_ldisc_halt(struct tty_struct *tty)
 {
+       int scheduled;
        clear_bit(TTY_LDISC, &tty->flags);
-       return cancel_work_sync(&tty->port->buf.work);
+       scheduled = cancel_work_sync(&tty->port->buf.work);
+       set_bit(TTY_LDISC_HALTED, &tty->flags);
+       return scheduled;
 }
 
 /**
@@ -820,6 +824,7 @@ void tty_ldisc_hangup(struct tty_struct *tty)
        clear_bit(TTY_LDISC, &tty->flags);
        tty_unlock(tty);
        cancel_work_sync(&tty->port->buf.work);
+       set_bit(TTY_LDISC_HALTED, &tty->flags);
        mutex_unlock(&tty->ldisc_mutex);
 retry:
        tty_lock(tty);

diff --git a/include/linux/tty.h b/include/linux/tty.h
index d3548f8..66ae020 100644 (file)
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -315,6 +315,7 @@ struct tty_file_private {
 #define TTY_NO_WRITE_SPLIT     17      /* Preserve write boundaries to driver */
 #define TTY_HUPPED             18      /* Post driver->hangup() */
 #define TTY_HUPPING            21      /* ->hangup() in progress */
+#define TTY_LDISC_HALTED       22      /* Line discipline is halted */
 
 #define TTY_WRITE_FLUSH(tty) tty_write_flush((tty))