From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932496Ab1EFA0A (ORCPT ); Thu, 5 May 2011 20:26:00 -0400 Received: from kroah.org ([198.145.64.141]:37285 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932455Ab1EFAZz (ORCPT ); Thu, 5 May 2011 20:25:55 -0400 X-Mailbox-Line: From gregkh@clark.kroah.org Thu May 5 17:22:17 2011 Message-Id: <20110506002217.166675829@clark.kroah.org> User-Agent: quilt/0.48-16.4 Date: Thu, 05 May 2011 17:21:46 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Peter Zijlstra , Ingo Molnar Subject: [121/143] init, sched: Fix race between init and kthreadd In-Reply-To: <20110506002311.GA15354@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.32-longterm review patch. If anyone has any objections, please let us know. ------------------ From: Peter Zijlstra commit b433c3d4549ae74935b585115f076c6fb7bc48fe upstream. Ilya reported that on a very slow machine he could reliably reproduce a race between forking init and kthreadd. We first fork init so that it obtains pid-1, however since the scheduler is already fully running at this point it can preempt and run the init thread before we spawn and set kthreadd_task. The init thread can then attempt spawning kthreads without kthreadd being present which results in an OOPS. Reported-by: Ilya Loginov Signed-off-by: Peter Zijlstra Acked-by: Linus Torvalds LKML-Reference: <1277736661.3561.110.camel@laptop> Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- init/main.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) --- a/init/main.c +++ b/init/main.c @@ -407,16 +407,24 @@ static void __init setup_command_line(ch * gcc-3.4 accidentally inlines this function, so use noinline. */ +static __initdata DECLARE_COMPLETION(kthreadd_done); + static noinline void __init_refok rest_init(void) __releases(kernel_lock) { int pid; rcu_scheduler_starting(); + /* + * We need to spawn init first so that it obtains pid-1, however + * the init task will end up wanting to create kthreads, which, if + * we schedule it before we create kthreadd, will OOPS. + */ kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND); numa_default_policy(); pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES); kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns); + complete(&kthreadd_done); unlock_kernel(); /* @@ -841,6 +849,10 @@ static noinline int init_post(void) static int __init kernel_init(void * unused) { + /* + * Wait until kthreadd is all set-up. + */ + wait_for_completion(&kthreadd_done); lock_kernel(); /*