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SubjectRe: Success: tty_io flush_to_ldisc() error message triggered
In-Reply-To: <44C2307C.9060607@microgate.com>

On Sat, 22 Jul 2006 09:04:44 -0500, Paul Fulghum wrote:

> That confirms my thoughts on what went wrong:
> multiple copies of the queued work (flush_to_ldisc)
> running in parallel and corrupting the free buffer list.
>
> A cleaner fix for this is already
> in the 2.6.18 rc series.

The cleaner fix looks more intrusive, though.

Is this simpler change (what I'm running but without the warning
messages) the preferred fix for -stable?


From: Paul Fulghum <paulkf@microgate.com>

Serialize flush_to_ldisc() per-device. Fixes free list corruption
that causes lockup on SMP systems.

Signed-off-by: Paul Fulghum <paulkf@microgate.com>
Acked-by: Chuck Ebbert <76306.1226@compuserve.com>

--- 2.6.16.20-d4.orig/include/linux/tty.h
+++ 2.6.16.20-d4/include/linux/tty.h
@@ -266,6 +266,7 @@ struct tty_struct {
#define TTY_PTY_LOCK 16 /* pty private */
#define TTY_NO_WRITE_SPLIT 17 /* Preserve write boundaries to driver */
#define TTY_HUPPED 18 /* Post driver->hangup() */
+#define TTY_FLUSHING 19 /* Flushing tty buffers to line discipline */

#define TTY_WRITE_FLUSH(tty) tty_write_flush((tty))

--- 2.6.16.20-d4.orig/drivers/char/tty_io.c
+++ 2.6.16.20-d4/drivers/char/tty_io.c
@@ -2780,10 +2780,8 @@ static void flush_to_ldisc(void *private
if (disc == NULL) /* !TTY_LDISC */
return;

- if (test_bit(TTY_DONT_FLIP, &tty->flags)) {
- /*
- * Do it after the next timer tick:
- */
+ if (test_bit(TTY_DONT_FLIP, &tty->flags) ||
+ test_and_set_bit(TTY_FLUSHING, &tty->flags)) {
schedule_delayed_work(&tty->buf.work, 1);
goto out;
}
@@ -2805,6 +2803,7 @@ static void flush_to_ldisc(void *private
tty_buffer_free(tty, tbuf);
}
spin_unlock_irqrestore(&tty->buf.lock, flags);
+ clear_bit(TTY_FLUSHING, &tty->flags);
out:
tty_ldisc_deref(disc);
}
--
Chuck
-
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