From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754789Ab0F1U0a (ORCPT ); Mon, 28 Jun 2010 16:26:30 -0400 Received: from hera.kernel.org ([140.211.167.34]:45920 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752849Ab0F1U03 (ORCPT ); Mon, 28 Jun 2010 16:26:29 -0400 Date: Mon, 28 Jun 2010 20:24:46 GMT From: tip-bot for Peter Zijlstra Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@redhat.com, torvalds@linux-foundation.org, a.p.zijlstra@chello.nl, peterz@infradead.org, isloginov@gmail.com, tglx@linutronix.de, mingo@elte.hu Reply-To: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, torvalds@linux-foundation.org, peterz@infradead.org, tglx@linutronix.de, isloginov@gmail.com, mingo@elte.hu In-Reply-To: <1277736661.3561.110.camel@laptop> References: <1277736661.3561.110.camel@laptop> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/urgent] init, sched: Fix race between init and kthreadd Message-ID: Git-Commit-ID: b433c3d4549ae74935b585115f076c6fb7bc48fe X-Mailer: tip-git-log-daemon MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.3 (hera.kernel.org [127.0.0.1]); Mon, 28 Jun 2010 20:24:59 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: b433c3d4549ae74935b585115f076c6fb7bc48fe Gitweb: http://git.kernel.org/tip/b433c3d4549ae74935b585115f076c6fb7bc48fe Author: Peter Zijlstra AuthorDate: Mon, 28 Jun 2010 16:51:01 +0200 Committer: Ingo Molnar CommitDate: Mon, 28 Jun 2010 18:21:30 +0200 init, sched: Fix race between init and kthreadd 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 --- init/main.c | 12 ++++++++++++ 1 files changed, 12 insertions(+), 0 deletions(-) diff --git a/init/main.c b/init/main.c index 3bdb152..633442f 100644 --- a/init/main.c +++ b/init/main.c @@ -422,18 +422,26 @@ 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(); /* @@ -855,6 +863,10 @@ 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(); /*