From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754119AbXDWRrj (ORCPT ); Mon, 23 Apr 2007 13:47:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754116AbXDWRrj (ORCPT ); Mon, 23 Apr 2007 13:47:39 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:41874 "EHLO ebiederm.dsl.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754118AbXDWRri (ORCPT ); Mon, 23 Apr 2007 13:47:38 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Oleg Nesterov Cc: Christoph Hellwig , Andrew Morton , containers@lists.osdl.org, linux-kernel@vger.kernel.org, Marcel Holtmann , rusty@rustcorp.com.au Subject: Re: [PATCH] kthread: Spontaneous exit support References: <1176969596686-git-send-email-ebiederm@xmission.com> <20070419162459.af7a182c.akpm@linux-foundation.org> <20070422194455.GA18561@infradead.org> <20070423112537.GA21941@infradead.org> <20070423165810.GA188@tv-sign.ru> Date: Mon, 23 Apr 2007 11:45:51 -0600 In-Reply-To: <20070423165810.GA188@tv-sign.ru> (Oleg Nesterov's message of "Mon, 23 Apr 2007 20:58:10 +0400") Message-ID: User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Oleg Nesterov writes: > On 04/23, Christoph Hellwig wrote: >> >> On Sun, Apr 22, 2007 at 09:12:55PM -0600, Eric W. Biederman wrote: >> > >> > This patch implements the kthread helper functions kthread_start >> > and kthread_end which make it simple to support a kernel thread >> > that may decided to exit on it's own before we request it to. >> > It is still assumed that eventually we will get around to requesting >> > that the kernel thread stop. >> >> I don't think having to parallel APIs is a good idea, people will >> get utterly confused which one to use. Better always grab a reference >> in kthread_create and drop it in kthread_stop. For normal thread >> no change in behaviour and only slightly more code in the slowpath. >> >> Of course it will need an audit for half-assed kthread conversion >> first to avoid task_struct reference count leaks. > > In that case it is better to grab a reference in kthread(). This also > close the race when a new thread is woken (freezer) and exits before > kthread_create() does get_task_struct(). > >> In addition to that kthrad_end implementation look wrong. When >> the kthread has exited prematurely no one will call complete >> on kthread_stop_info.done before it's been setup. > > This is not true anymore, see another patch from Eric > > kthread-enhance-kthread_stop-to-abort-interruptible-sleeps.patch Ok. Thinking about it I agree with Christoph that parallel API's can be a problem. However we do still need to support kernel threads where kthread_stop will never be called. There appear to be a few legitimate cases where someone wants to fire off a thread and have it do some work but don't care at all for stopping it before it is done. So I propose we add a kthread_orphan as a basic primitive to decrement the count on the task_struct if we want a kthread to simply exit after it has done some work. And as a helper function we can have a kthread_run_orphan. I think having a kthread_orphan will document what we are doing better and make it easy to find kernel threads that don't use kthread_stop. The pain is that this requires an audit of all kernel kthread creators so that we call kthread_orphan on the right ones, or else we will have a task_struct leak. At least that isn't a fatal condition. Eric