From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756076AbcDDSVo (ORCPT ); Mon, 4 Apr 2016 14:21:44 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55157 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754693AbcDDSVm (ORCPT ); Mon, 4 Apr 2016 14:21:42 -0400 Date: Mon, 4 Apr 2016 13:21:38 -0500 From: Josh Poimboeuf To: Miroslav Benes Cc: Jiri Kosina , Jessica Yu , linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, Vojtech Pavlik Subject: Re: [RFC PATCH v1.9 12/14] livepatch: create per-task consistency model Message-ID: <20160404182138.pjze2fvtmknq2ksq@treble.redhat.com> References: <74a2b37cea7a64a185e50876dba031137aa59a24.1458933243.git.jpoimboe@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 31, 2016 at 03:12:39PM +0200, Miroslav Benes wrote: > On Fri, 25 Mar 2016, Josh Poimboeuf wrote: > > [...] > > > diff --git a/kernel/fork.c b/kernel/fork.c > > index d277e83..27b181e 100644 > > --- a/kernel/fork.c > > +++ b/kernel/fork.c > > @@ -76,6 +76,7 @@ > > #include > > #include > > #include > > +#include > > > > #include > > #include > > @@ -1615,6 +1616,7 @@ static struct task_struct *copy_process(unsigned long clone_flags, > > total_forks++; > > spin_unlock(¤t->sighand->siglock); > > syscall_tracepoint_update(p); > > + klp_update_task_universe(p); > > Shouldn't we copy transition and TIF from the parent? I deal with a race > in kgraft and the solution seems to be this code exactly at this place in > copy_process(). I need to think about it. Hm, can you explain why it should be copied from the parent? I'm thinking the above code is correct for today, but it should still be changed to be more future-proof. Here's my thinking: A forked task starts out with no stack, so if I understand correctly, it can safely start out in the goal universe, regardless of which universe its parent belongs to. However, the current ret_from_fork code is a mess, and Andy Lutomirski has mentioned that he would like to give newly forked tasks a proper stack such that instead of jumping to ret_from_fork, they would just return from schedule(). In that case, it would no longer be safe to start the new task in the goal universe because it could be "sleeping" on a to-be-patched function. So for proper future proofing, newly forked tasks should be started in the initial universe (rather than starting in the goal universe or inheriting the parent's universe). They can then be transitioned over to the goal universe like any other task. How does that sound? -- Josh