From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030490AbXDMVbh (ORCPT ); Fri, 13 Apr 2007 17:31:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030502AbXDMVbh (ORCPT ); Fri, 13 Apr 2007 17:31:37 -0400 Received: from smtp.osdl.org ([65.172.181.24]:53233 "EHLO smtp.osdl.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030490AbXDMVbg (ORCPT ); Fri, 13 Apr 2007 17:31:36 -0400 Date: Fri, 13 Apr 2007 14:31:04 -0700 From: Andrew Morton To: Oleg Nesterov Cc: Davide Libenzi , "Eric W. Biederman" , Ingo Molnar , Linus Torvalds , "Rafael J. Wysocki" , Roland McGrath , Rusty Russell , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] make kthread_create() more scalable Message-Id: <20070413143104.99a1eeb9.akpm@linux-foundation.org> In-Reply-To: <20070413130201.GA170@tv-sign.ru> References: <20070413130201.GA170@tv-sign.ru> X-Mailer: Sylpheed version 2.2.7 (GTK+ 2.8.6; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 13 Apr 2007 17:02:01 +0400 Oleg Nesterov wrote: > If kernel_thread(kthread) succeeds, kthread() can not fail on its path to > complete(&create->started) + schedule(). After that it can't be woken because > nobody can see the new task yet. This means: > > - we don't need tasklist_lock for find_task_by_pid(). > > - create_kthread() doesn't need to wait for create->started. Instead, > kthread_create() first waits for create->created to get the result of > kernel_thread(), then waits for create->started to synchronize with > kthread(). Why don't we need tasklist_lock for find_task_by_pid()? I'd have though that we'd at least need rcu_read_lock(), and I'm not sure that the implicit understanding of pid-management internals here is a great idea.