From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755054Ab0F1Ovg (ORCPT ); Mon, 28 Jun 2010 10:51:36 -0400 Received: from casper.infradead.org ([85.118.1.10]:56100 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754901Ab0F1Ovd convert rfc822-to-8bit (ORCPT ); Mon, 28 Jun 2010 10:51:33 -0400 Subject: [PATCH] init: Fix race between init and kthreadd -v3 From: Peter Zijlstra To: Ingo Molnar Cc: Ilya Loginov , torvalds@linux-foundation.org, linux-kernel@vger.kernel.org In-Reply-To: <20100628141927.GA9306@elte.hu> References: <20100624001148.61e9da1c.isloginov@gmail.com> <1277385096.1875.974.camel@laptop> <20100624172334.ca7e9bef.isloginov@gmail.com> <1277715689.1875.1104.camel@laptop> <1277725997.3561.6.camel@laptop> <20100628141927.GA9306@elte.hu> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Mon, 28 Jun 2010 16:51:01 +0200 Message-ID: <1277736661.3561.110.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2010-06-28 at 16:19 +0200, Ingo Molnar wrote: > I think you may be using a mutex as a completion in essence. Why not use > completions instead? Totally forgot about those things.. Yes they fit perfectly. --- Subject: init: Fix race between init and kthreadd -v2 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 --- init/main.c | 12 ++++++++++++ 1 files changed, 12 insertions(+), 0 deletions(-) diff --git a/init/main.c b/init/main.c index e2a2bf3..2280f63 100644 --- a/init/main.c +++ b/init/main.c @@ -420,18 +420,26 @@ static void __init setup_command_line(char *command_line) * 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); rcu_read_lock(); kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns); rcu_read_unlock(); + complete(&kthreadd_done); unlock_kernel(); /* @@ -847,6 +855,10 @@ 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(); /*