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 5573AC4360C for ; Tue, 8 Oct 2019 19:50:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2C0CD218DE for ; Tue, 8 Oct 2019 19:50:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729602AbfJHTuZ (ORCPT ); Tue, 8 Oct 2019 15:50:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:42322 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729385AbfJHTuZ (ORCPT ); Tue, 8 Oct 2019 15:50:25 -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 7BEC321835; Tue, 8 Oct 2019 19:50:24 +0000 (UTC) Date: Tue, 8 Oct 2019 15:50:22 -0400 From: Steven Rostedt To: Joe Lawrence Cc: Miroslav Benes , mingo@redhat.com, jpoimboe@redhat.com, jikos@kernel.org, pmladek@suse.com, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org Subject: Re: [PATCH 0/3] ftrace: Introduce PERMANENT ftrace_ops flag Message-ID: <20191008155022.61db3108@gandalf.local.home> In-Reply-To: <20191008193534.GA16675@redhat.com> References: <20191007081714.20259-1-mbenes@suse.cz> <20191008193534.GA16675@redhat.com> 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 Tue, 8 Oct 2019 15:35:34 -0400 Joe Lawrence wrote: > > 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 believe I suggested the "PERMANENT" flag, but disabling ftrace_enable may be another approach. Might be much easier to maintain. > > As for the approach in this patchset, is it consistent that livepatches > loaded after setting ftrace_enabled to 0 will successfully load, but not > execute their new code... but then when ftrace_enabled is toggled, the > new livepatch code remains on? > > For example: > > 1 - Turn ftrace_enabled off and load the /proc/cmdline livepatch test > case, note that it reports a success patching transition, but > doesn't run new its code: > > % dmesg -C > % sysctl kernel.ftrace_enabled=0 > kernel.ftrace_enabled = 0 > % insmod lib/livepatch/test_klp_livepatch.ko > % echo $? > 0 > % dmesg > [ 450.579980] livepatch: enabling patch 'test_klp_livepatch' > [ 450.581243] livepatch: 'test_klp_livepatch': starting patching transition > [ 451.942971] livepatch: 'test_klp_livepatch': patching complete > % cat /proc/cmdline > BOOT_IMAGE=(hd0,msdos1)/boot/vmlinuz-5.4.0-rc2+ root=UUID=c42bb089-b5c1-4e17-82bd-132f55bee54c ro console=ttyS0 console=ttyS0,115200n8 no_timer_check net.ifnames=0 crashkernel=auto > > 2 - Turn ftrace_enabled on and see that the livepatch now works: > > % sysctl kernel.ftrace_enabled=1 > kernel.ftrace_enabled = 1 > % cat /proc/cmdline > test_klp_livepatch: this has been live patched > > 3 - Turn ftrace_enabled off and see that it's still enabled: > > % sysctl kernel.ftrace_enabled=0 > kernel.ftrace_enabled = 0 > % cat /proc/cmdline > test_klp_livepatch: this has been live patched > > Steps 2 and 3 match the behavior described by the patchset, but I was > particularly wondering what you thought about step 1. > > IMHO, I would expect step 1 to fully enable the livepatch, or at the > very least, not report a patch transition (though that may confuse > userspace tools waiting for that report). > I think I like your idea better. To prevent ftrace_enable from being disabled if a "permanent" option is set. Then we only need to have a permanent flag for the ftrace_ops, that will disable the ftrace_enable from being cleared. We can also prevent the ftrace_ops from being loaded if ftrace_enable is not set and the ftrace_ops has the PERMANENT flag set. -- Steve