From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 670A5C47404 for ; Wed, 9 Oct 2019 14:26:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 44D9A218DE for ; Wed, 9 Oct 2019 14:26:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731214AbfJIO06 (ORCPT ); Wed, 9 Oct 2019 10:26:58 -0400 Received: from mail.kernel.org ([198.145.29.99]:47336 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727769AbfJIO05 (ORCPT ); Wed, 9 Oct 2019 10:26:57 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 869C220B7C; Wed, 9 Oct 2019 14:26:56 +0000 (UTC) Date: Wed, 9 Oct 2019 10:26:54 -0400 From: Steven Rostedt To: Petr Mladek Cc: Joe Lawrence , Miroslav Benes , jikos@kernel.org, jpoimboe@redhat.com, mingo@redhat.com, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org Subject: Re: [PATCH 0/3] ftrace: Introduce PERMANENT ftrace_ops flag Message-ID: <20191009102654.501ad7c3@gandalf.local.home> In-Reply-To: <20191009112234.bi7lvp4pvmna26vz@pathway.suse.cz> References: <20191007081714.20259-1-mbenes@suse.cz> <20191008193534.GA16675@redhat.com> <20191009112234.bi7lvp4pvmna26vz@pathway.suse.cz> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: live-patching-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Wed, 9 Oct 2019 13:22:34 +0200 Petr Mladek wrote: > > Hi Miroslav, > > > > I wonder if the opposite would be more intuitive: when ftrace_enabled is > > not set, don't allow livepatches to register ftrace filters and > > likewise, don't allow ftrace_enabled to be unset if any livepatches are > > already registered. I guess you could make an argument either way, but > > just offering another option. Perhaps livepatches should follow similar > > behavior of other ftrace clients (like perf probes?) > > I am not sure that I understand it correctly. > > ftrace_enables is a global flag. My expectation is that it can be > manipulated at any time. But it should affect only ftrace handlers > without FTRACE_OPS_FL_PERMANENT flag. No, it should affect *all* ftrace_ops (which it currently does). The addition of the "PERMANENT" flag was going to change that to what you are saying here. But thinking about this more, I believe that is the wrong approach. > > By other words, the handlers with FTRACE_OPS_FL_PERMANENT flag and > only these handlers should ignore the global flag. > > To be even more precise. If a function has registered more ftrace > handlers then the global ftrace_enable setting shold affect only > the handlers without the flag. > > Is this the plan, please? I think Joe's approach is much easier to understand and implement. The "ftrace_enabled" is a global flag, and affects all things ftrace (the function bindings). What this patch was doing, was what you said. Make ftrace_enabled only affect the ftrace_ops without the "PERMANENT" flag set. But that is complex and requires a bit more accounting in the ftrace system. Something I think we should try to avoid. What we are now proposing, is that if "ftrace_enabled" is not set, the register_ftrace_function() will fail if the ftrace_ops passed to it has the PERMANENT flag set (which would cause live patching to fail to load). It also means that if ftrace_enabled was set, and we load a ftrace_ops with the PERMANENT flag set, and the user tries to clear ftrace_enabled, that operation will fail. That is, you will not be able to clear ftrace_enabled if a ftrace_ops is loaded with the PERMANENT flag set. You will need to have your live kernel patching user space tooling make sure that ftrace_enabled is set before loading, but that shouldn't be a problem. Does that make sense? -- Steve