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Subject[PATCH v3 01/23] tty: Add diagnostic for halted line discipline
Date
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>
---
drivers/tty/n_tty.c | 8 ++++++++
drivers/tty/tty_ldisc.c | 45 +++++++++++++++++++++++++--------------------
include/linux/tty.h | 1 +
3 files changed, 34 insertions(+), 20 deletions(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 19083ef..bf6958b 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -152,6 +152,12 @@ 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);
}
}
@@ -1644,6 +1650,8 @@ 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..904bf75 100644
--- 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);
@@ -498,26 +499,6 @@ static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
}

/**
- * tty_ldisc_halt - shut down the line discipline
- * @tty: tty device
- *
- * Shut down the line discipline and work queue for this tty device.
- * The TTY_LDISC flag being cleared ensures no further references can
- * be obtained while the delayed work queue halt ensures that no more
- * data is fed to the ldisc.
- *
- * You need to do a 'flush_scheduled_work()' (outside the ldisc_mutex)
- * in order to make sure any currently executing ldisc work is also
- * flushed.
- */
-
-static int tty_ldisc_halt(struct tty_struct *tty)
-{
- clear_bit(TTY_LDISC, &tty->flags);
- return cancel_work_sync(&tty->port->buf.work);
-}
-
-/**
* tty_ldisc_flush_works - flush all works of a tty
* @tty: tty device to flush works for
*
@@ -547,6 +528,29 @@ static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout)
}

/**
+ * tty_ldisc_halt - shut down the line discipline
+ * @tty: tty device
+ *
+ * Shut down the line discipline and work queue for this tty device.
+ * The TTY_LDISC flag being cleared ensures no further references can
+ * be obtained while the delayed work queue halt ensures that no more
+ * data is fed to the ldisc.
+ *
+ * You need to do a 'flush_scheduled_work()' (outside the ldisc_mutex)
+ * in order to make sure any currently executing ldisc work is also
+ * flushed.
+ */
+
+static int tty_ldisc_halt(struct tty_struct *tty)
+{
+ int scheduled;
+ clear_bit(TTY_LDISC, &tty->flags);
+ scheduled = cancel_work_sync(&tty->port->buf.work);
+ set_bit(TTY_LDISC_HALTED, &tty->flags);
+ return scheduled;
+}
+
+/**
* tty_set_ldisc - set line discipline
* @tty: the terminal to set
* @ldisc: the line discipline
@@ -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 c75d886..7aa4be6 100644
--- 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))

--
1.8.1.2


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