From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754332Ab2KVTAM (ORCPT ); Thu, 22 Nov 2012 14:00:12 -0500 Received: from 95-31-19-74.broadband.corbina.ru ([95.31.19.74]:45018 "EHLO 95-31-19-74.broadband.corbina.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753875Ab2KVTAG (ORCPT ); Thu, 22 Nov 2012 14:00:06 -0500 Message-ID: <50ADC7B5.7010206@ilyx.ru> Date: Thu, 22 Nov 2012 10:35:33 +0400 From: Ilya Zykov User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:16.0) Gecko/20121026 Thunderbird/16.0.2 MIME-Version: 1.0 To: andrew mcgregor CC: Alan Cox , Greg Kroah-Hartman , linux-kernel@vger.kernel.org Subject: Re: [PATCH] tty: Add driver unthrottle in ioctl(...,TCFLSH,..). References: <50AD43DB.4030800@ilyx.ru> <20121121213037.154306da@pyramind.ukuu.org.uk> <50AD4A01.7060500@ilyx.ru> <50AE2CE30200003600026B9A@gwia.alliedtelesyn.co.nz> <50ADAA26.7080103@ilyx.ru> <50AE6E050200003600026BD7@gwia.alliedtelesyn.co.nz> In-Reply-To: <50AE6E050200003600026BD7@gwia.alliedtelesyn.co.nz> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 22.11.2012 9:25, andrew mcgregor wrote: > > >>>> On 11/22/2012 at 05:29 PM, in message <50ADAA26.7080103@ilyx.ru>, Ilya Zykov > wrote: >> On 22.11.2012 4:47, andrew mcgregor wrote: >>> >>> >>>>>> On 11/22/2012 at 10:39 AM, in message <50AD4A01.7060500@ilyx.ru>, Ilya Zykov >>> wrote: >>>> On 22.11.2012 1:30, Alan Cox wrote: >>>>>> Function reset_buffer_flags() also invoked during the >>>>>> ioctl(...,TCFLSH,..). At the time of request we can have full buffers >>>>>> and throttled driver too. If we don't unthrottle driver, we can get >>>>>> forever throttled driver, because after request, we will have >>>>>> empty buffers and throttled driver and there is no place to unthrottle >>>> driver. >>>>>> It simple reproduce with "pty" pair then one side sleep on tty->write_wait, >>>>>> and other side do ioctl(...,TCFLSH,..). Then there is no place to do >>>> writers wake up. >>>>> >>>>> >>>>> So instead of revertng it why not just fix it ? Just add an argument to >>>>> the reset_buffer_flags function to indicate if unthrottling is permitted. >>>>> >>>>> Alan >>>>> >>>> Because in my opinion, unthrottling permitted always, except release >>>> last filp (tty->count == 0) >>> >>> Maybe so, but the patch was there in the first place to resolve an actual >> observed bug, where a driver would lock up. So the behaviour needs >> preserved. >>> >>> Andrew >>> >> >> Maybe it was wrong driver, unfortunately, I didn't find full information >> about this bug. As an example, if driver indirectly call >> reset_buffer_flags() in driver's close() function it will be before >> decrement last (tty->count). > > Well, the driver in question was just 8250.c, so you should be able to see that the original condition can exist. > > Here's the commit message again: > > tty: fix "IRQ45: nobody cared" > > Unthrottling the TTY during close ends up enabling interrupts > on a device not on the active list, which will never have the > interrupts cleared. Doctor, it hurts when I do this. > >>>> On 6/2/2011 at 01:56 AM, in message <20110601145608.3e586e16@bob.linux.org.uk>, Alan Cox wrote: >> On Wed, 01 Jun 2011 10:34:07 +1200 >> "andrew mcgregor" wrote: >>> The LKML message >>> http://kerneltrap.org/mailarchive/linux-kernel/2010/2/25/4541847from >>> February doesn't seem to have been resolved since. We struck the >>> issue, and the patch below (against 2.6.32) fixes it. Should I >>> supply a patch against 3.0.0rc? >> >> I think that would be sensible. I don't actually see how you hit it as >> the IRQ ought to be masked by then but it's certainly wrong for n_tty >> to be calling into check_unthrottle at that point. >> >> So yes please send a patch with a suitable Signed-off-by: line to >> linux-serial and cc GregKH as well. >> >> Alan > > Signed-off-by: Andrew McGregor > Signed-off-by: Greg Kroah-Hartman > > What part of this no longer applies? I'm happy enough if you can prove that this can't happen any more, but otherwise the fix should remain. > > Andrew This patch must help for 8250.c diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index a21dc8e..2e197c3 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -1288,8 +1288,6 @@ static void uart_close(struct tty_struct *tty, struct file *filp) uart_shutdown(tty, state); uart_flush_buffer(tty); - tty_ldisc_flush(tty); - tty_port_tty_set(port, NULL); spin_lock_irqsave(&port->lock, flags); tty->closing = 0;