Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756252AbcDDTAd (ORCPT ); Mon, 4 Apr 2016 15:00:33 -0400 Received: from jablonecka.jablonka.cz ([91.219.244.36]:52872 "EHLO jablonecka.jablonka.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753305AbcDDTAb (ORCPT ); Mon, 4 Apr 2016 15:00:31 -0400 X-Greylist: delayed 1947 seconds by postgrey-1.27 at vger.kernel.org; Mon, 04 Apr 2016 15:00:31 EDT Date: Mon, 4 Apr 2016 20:27:59 +0200 From: Vojtech Pavlik To: Josh Poimboeuf Cc: Miroslav Benes , Jiri Kosina , Jessica Yu , linux-kernel@vger.kernel.org, live-patching@vger.kernel.org Subject: Re: [RFC PATCH v1.9 12/14] livepatch: create per-task consistency model Message-ID: <20160404182759.GA10777@suse.cz> References: <74a2b37cea7a64a185e50876dba031137aa59a24.1458933243.git.jpoimboe@redhat.com> <20160404182138.pjze2fvtmknq2ksq@treble.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160404182138.pjze2fvtmknq2ksq@treble.redhat.com> X-Bounce-Cookie: It's a lemon tree, dear Watson! User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1320 Lines: 32 On Mon, Apr 04, 2016 at 01:21:38PM -0500, Josh Poimboeuf wrote: > 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? How could a newly forked task start in the old universe if its parent has already been migrated? Any context it inherits will already be from the new universe. -- Vojtech Pavlik Director SuSE Labs