From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752395AbeBAPSP (ORCPT <rfc822;w@1wt.eu>);
        Thu, 1 Feb 2018 10:18:15 -0500
Received: from mx1.redhat.com ([209.132.183.28]:15410 "EHLO mx1.redhat.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1752064AbeBAPSL (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 1 Feb 2018 10:18:11 -0500
Date: Thu, 1 Feb 2018 09:18:07 -0600
From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Miroslav Benes <mbenes@suse.cz>
Cc: Joe Lawrence <joe.lawrence@redhat.com>, Petr Mladek <pmladek@suse.com>,
        jikos@kernel.org, Jason Baron <jbaron@akamai.com>, jeyu@kernel.org,
        Evgenii Shatokhin <eshatokhin@virtuozzo.com>,
        linux-kernel@vger.kernel.org, live-patching@vger.kernel.org
Subject: Re: PATCH v6 0/6] livepatch: Atomic replace feature
Message-ID: <20180201151807.xjrldhmwwuot4c2o@treble>
References: <20180125160203.28959-1-pmladek@suse.com>
 <alpine.LSU.2.21.1802011350200.26656@pobox.suse.cz>
 <1dd714ce-8d11-78b9-51f0-2b71734949e1@redhat.com>
 <alpine.LSU.2.21.1802011605450.29533@pobox.suse.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <alpine.LSU.2.21.1802011605450.29533@pobox.suse.cz>
User-Agent: Mutt/1.6.0.1 (2016-04-01)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, Feb 01, 2018 at 04:08:14PM +0100, Miroslav Benes wrote:
> On Thu, 1 Feb 2018, Joe Lawrence wrote:
> 
> > On 02/01/2018 08:49 AM, Miroslav Benes wrote:
> > > 
> > > Well, one more thing. I think there is a problem with shadow variables. 
> > > Similar to callbacks situation. Shadow variables cannot be destroyed the 
> > > way it is shown in our samples. Cumulative patches want to preserve 
> > > everything as much as possible. If I'm right, it should be mentioned in 
> > > the documentation.
> > 
> > Are you talking about using klp_shadow_free_all() call in a module_exit
> > routine?  Yeah, I think in this case, that responsibility would be
> > passed to the newly loaded cumulative patch, right?
> 
> Yes, but we haven't got an option not to call it here (as with callbacks, 
> where we can omit callbacks completely with atomic replace patches). A 
> live patch author must be aware of this and use shadow variables 
> appropriately.

So maybe we should recommend that shadow variables generally be freed
from a post-unpatch callback.

-- 
Josh