From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751516AbWFLSGX (ORCPT ); Mon, 12 Jun 2006 14:06:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751517AbWFLSGX (ORCPT ); Mon, 12 Jun 2006 14:06:23 -0400 Received: from adsl-70-250-156-241.dsl.austtx.swbell.net ([70.250.156.241]:55947 "EHLO gw.microgate.com") by vger.kernel.org with ESMTP id S1751516AbWFLSGW (ORCPT ); Mon, 12 Jun 2006 14:06:22 -0400 Subject: Re: 2.6.16.18 kernel freezes while pppd is exiting From: Paul Fulghum To: Chuck Ebbert <76306.1226@compuserve.com> Cc: linux-kernel , Alan Cox In-Reply-To: <200606121239_MC3-1-C23E-9AF9@compuserve.com> References: <200606121239_MC3-1-C23E-9AF9@compuserve.com> Content-Type: text/plain Date: Mon, 12 Jun 2006 13:06:12 -0500 Message-Id: <1150135572.6065.8.camel@amdx2.microgate.com> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-4.fc4) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2006-06-12 at 12:36 -0400, Chuck Ebbert wrote: > I already applied this, which should keep it from freezing and > will print a warning, so I will apply your patch and then check > the log every time pppd exits. Your debug output seems like a good idea for catching the mechanism of reentrance on flush_to_ldisc (if it is happening at all). My reading of the workqueue code is that the work function can run in parallel on a multiple CPU system. The default workqueue has multiple, per CPU queues, and the pending bit for the work item is cleared before execution. This would allow the work item to be requeued for another CPU while the function is executing. (If I'm wrong, I would be happy to be told why) Anyways, if I can impose on you to use this version with debug output, it would help clarify this. If the DONT_FLIP debug output happens too often and fills you syslog, comment out that part. --- a/include/linux/tty.h 2006-06-09 09:33:16.000000000 -0500 +++ b/include/linux/tty.h 2006-06-12 09:22:10.000000000 -0500 @@ -267,6 +267,7 @@ 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)) --- a/drivers/char/tty_io.c 2006-06-12 12:54:37.000000000 -0500 +++ b/drivers/char/tty_io.c 2006-06-12 12:54:54.000000000 -0500 @@ -2786,9 +2786,12 @@ static void flush_to_ldisc(void *private return; if (test_bit(TTY_DONT_FLIP, &tty->flags)) { - /* - * Do it after the next timer tick: - */ + printk(KERN_ERR"flush_to_ldisc - TTY_DONT_FLIP set\n"); + schedule_delayed_work(&tty->buf.work, 1); + goto out; + } + if (test_and_set_bit(TTY_FLUSHING, &tty->flags)) { + printk(KERN_ERR"flush_to_ldisc - TTY_FLUSHING set, low_latency=%d\n", tty->low_latency); schedule_delayed_work(&tty->buf.work, 1); goto out; } @@ -2810,6 +2813,7 @@ 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); }