From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755942AbcCBCWI (ORCPT ); Tue, 1 Mar 2016 21:22:08 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:45788 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752781AbcCAXrK (ORCPT ); Tue, 1 Mar 2016 18:47:10 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Vegard Nossum , Richard Weinberger Subject: [PATCH 3.10 54/80] uml: flush stdout before forking Date: Tue, 1 Mar 2016 15:45:48 -0800 Message-Id: <20160301234351.348396417@linuxfoundation.org> X-Mailer: git-send-email 2.7.2 In-Reply-To: <20160301234349.667990420@linuxfoundation.org> References: <20160301234349.667990420@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Vegard Nossum commit 0754fb298f2f2719f0393491d010d46cfb25d043 upstream. I was seeing some really weird behaviour where piping UML's output somewhere would cause output to get duplicated: $ ./vmlinux | head -n 40 Checking that ptrace can change system call numbers...Core dump limits : soft - 0 hard - NONE OK Checking syscall emulation patch for ptrace...Core dump limits : soft - 0 hard - NONE OK Checking advanced syscall emulation patch for ptrace...Core dump limits : soft - 0 hard - NONE OK Core dump limits : soft - 0 hard - NONE This is because these tests do a fork() which duplicates the non-empty stdout buffer, then glibc flushes the duplicated buffer as each child exits. A simple workaround is to flush before forking. Signed-off-by: Vegard Nossum Signed-off-by: Richard Weinberger Signed-off-by: Greg Kroah-Hartman --- arch/um/os-Linux/start_up.c | 2 ++ 1 file changed, 2 insertions(+) --- a/arch/um/os-Linux/start_up.c +++ b/arch/um/os-Linux/start_up.c @@ -95,6 +95,8 @@ static int start_ptraced_child(void) { int pid, n, status; + fflush(stdout); + pid = fork(); if (pid == 0) ptrace_child();