linux-kernel - Re: Success: tty_io flush_to_ldisc() error message triggered

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Date:	Sat, 22 Jul 2006 12:07:00 -0400
From:	Chuck Ebbert <76306.1226@...puserve.com>
To:	Paul Fulghum <paulkf@...rogate.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-stable <stable@...nel.org>
Subject: Re: Success: tty_io flush_to_ldisc() error message triggered

In-Reply-To: <44C2307C.9060607@...rogate.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@...rogate.com>

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

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