From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757830Ab2KVVZZ (ORCPT ); Thu, 22 Nov 2012 16:25:25 -0500 Received: from gate.alliedtelesyn.co.nz ([202.49.72.33]:60133 "HELO gate.alliedtelesyn.co.nz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1755183Ab2KVVZW convert rfc822-to-8bit (ORCPT ); Thu, 22 Nov 2012 16:25:22 -0500 Message-Id: <50AE6E050200003600026BD7@gwia.alliedtelesyn.co.nz> X-Mailer: Novell GroupWise Internet Agent 8.0.2 Date: Thu, 22 Nov 2012 18:25:09 +1300 From: "andrew mcgregor" To: "Ilya Zykov" Cc: "Alan Cox" , "Greg Kroah-Hartman" , 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> In-Reply-To: <50ADAA26.7080103@ilyx.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>> 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