From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965132Ab2KVTeQ (ORCPT ); Thu, 22 Nov 2012 14:34:16 -0500 Received: from gate.alliedtelesyn.co.nz ([202.49.72.33]:59195 "HELO gate.alliedtelesyn.co.nz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1757043Ab2KVTeN convert rfc822-to-8bit (ORCPT ); Thu, 22 Nov 2012 14:34:13 -0500 X-Greylist: delayed 2530 seconds by postgrey-1.27 at vger.kernel.org; Thu, 22 Nov 2012 14:34:12 EST Message-Id: <50AE2CE30200003600026B9A@gwia.alliedtelesyn.co.nz> X-Mailer: Novell GroupWise Internet Agent 8.0.2 Date: Thu, 22 Nov 2012 13:47:15 +1300 From: "andrew mcgregor" To: "Ilya Zykov" , "Alan Cox" Cc: "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> In-Reply-To: <50AD4A01.7060500@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 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