From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Tue, 1 May 2001 12:04:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 1 May 2001 12:04:36 -0400 Received: from cisco7500-mainGW.gts.cz ([194.213.32.131]:37380 "EHLO bug.ucw.cz") by vger.kernel.org with ESMTP id ; Tue, 1 May 2001 12:04:18 -0400 Message-ID: <20010501180222.A18016@bug.ucw.cz> Date: Tue, 1 May 2001 18:02:22 +0200 From: Pavel Machek To: chet@po.cwru.edu, adam@yggdrasil.com Cc: bug-bash@gnu.org, linux-kernel@vger.kernel.org Subject: Re: Patch(?): bash-2.05/jobs.c loses interrupts In-Reply-To: <010430164417.AA94167.SM@nike.ins.cwru.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 0.93i In-Reply-To: <010430164417.AA94167.SM@nike.ins.cwru.edu>; from Chet Ramey on Mon, Apr 30, 2001 at 12:44:17PM -0400 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi! > > Linux-2.4.4 has a change, for which I must accept blame, > > where fork() runs the child first, reducing unnecessary copy-on-write > > page duplications, because the child will usually promptly do an > > exec(). I understand this is pretty standard in most unixes. > > > > Peter Osterlund noticed an annoying side effect of this, > > which I think is a bash bug. He wrote: > > > > > Another thing is that the bash loop "while true ; do /bin/true ; done" is > > > not possible to interrupt with ctrl-c. > > > > I have reproduced this problem on a single CPU system. > > I also modified my kernel to sometimes run the fork child first > > and sometimes not. In that case, that loop would sometimes > > abort on a control-C and sometimes ignore it, but ignoring it > > would not make the loop less likely to abort on another control-C. > > I'm pretty sure the control-C was being delivered only to the child > > due to a race condition in bash, which may be mandated by posix. > > Did you reconfigure and rebuild bash on your machine running the 2.4 > kernel, or just use a bash binary built on a previous kernel > version? This is nasty race condition. I do not believe you can test for it in configure. This might happen on 2.4.3 (occasionally) too. Kernel is permitted to do any kind of scheduling! Pavel > Bash has an autoconf test that will, if it detects the need to do so, > force the job control code to synchronize between parent and child > when setting up the process group for a new pipeline. It may be the > case that you have to reconfigure and rebuild bash to enable that code. > > Look for PGRP_PIPE in config.h. -- I'm pavel@ucw.cz. "In my country we have almost anarchy and I don't care." Panos Katsaloulis describing me w.r.t. patents at discuss@linmodems.org