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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7147C433F5 for ; Tue, 8 Mar 2022 09:51:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345492AbiCHJw1 (ORCPT ); Tue, 8 Mar 2022 04:52:27 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60314 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345407AbiCHJwZ (ORCPT ); Tue, 8 Mar 2022 04:52:25 -0500 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DE38941F9A; Tue, 8 Mar 2022 01:51:29 -0800 (PST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 972741F397; Tue, 8 Mar 2022 09:51:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1646733088; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=rfVbrz8lg45qGvZsPo5VEWHFttjSpHtZNvUX7LzR6Kc=; b=Q/14xt4hxFEC3EFzitSjjIrDHD20ZIPHE9sAhGZv9bDKNlVYDwQxQ0keoh7JHnFGf4p52u kUvVaHNzmJV/h77ISdtMNYNhu2SU04s8RNFKDq8cQyYjYn6xDRXCQzbtG1T37aJ16joRHJ 6MIEYsWQmkffQPzrMPkG85hpN6Iic+A= Received: from suse.cz (unknown [10.100.224.162]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 78E8DA3B87; Tue, 8 Mar 2022 09:51:28 +0000 (UTC) Date: Tue, 8 Mar 2022 10:51:28 +0100 From: Petr Mladek To: Chengming Zhou Cc: jpoimboe@redhat.com, jikos@kernel.org, mbenes@suse.cz, joe.lawrence@redhat.com, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] livepatch: Don't block removal of patches that are safe to unload Message-ID: References: <20220303105446.7152-1-zhouchengming@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220303105446.7152-1-zhouchengming@bytedance.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 2022-03-03 18:54:46, Chengming Zhou wrote: > module_put() is currently never called for a patch with forced flag, to block > the removal of that patch module that might still be in use after a forced > transition. > > But klp_force_transition() will set all patches on the list to be forced, since > commit d67a53720966 ("livepatch: Remove ordering (stacking) of the livepatches") > has removed stack ordering of the livepatches, it will cause all other patches can't > be unloaded after disabled even if they have completed the KLP_UNPATCHED transition. > > In fact, we don't need to set a patch to forced if it's a KLP_PATCHED forced > transition. It can still be unloaded safely as long as it has passed through > the consistency model in KLP_UNPATCHED transition. It really looks safe. klp_check_stack_func() makes sure that @new_func is not on the stack when klp_target_state == KLP_UNPATCHED. As a result, the system should not be using code from the livepatch module when KLP_UNPATCHED transition cleanly finished. > But the exception is when force transition of an atomic replace patch, we > have to set all previous patches to forced, or they will be removed at > the end of klp_try_complete_transition(). > > This patch only set the klp_transition_patch to be forced in KLP_UNPATCHED > case, and keep the old behavior when in atomic replace case. > > Signed-off-by: Chengming Zhou > --- > v2: interact nicely with the atomic replace feature noted by Miroslav. > --- > kernel/livepatch/transition.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c > index 5683ac0d2566..34ffb8c014ed 100644 > --- a/kernel/livepatch/transition.c > +++ b/kernel/livepatch/transition.c > @@ -641,6 +641,10 @@ void klp_force_transition(void) > for_each_possible_cpu(cpu) > klp_update_patch_state(idle_task(cpu)); > > - klp_for_each_patch(patch) > - patch->forced = true; > + if (klp_target_state == KLP_UNPATCHED) > + klp_transition_patch->forced = true; > + else if (klp_transition_patch->replace) { > + klp_for_each_patch(patch) > + patch->forced = true; This works only because there is should be only one patch when klp_target_state == KLP_UNPATCHED and klp_transition_patch->forced == true. But it is a bit tricky. I would do it the other way: if (klp_transition_patch->replace) { klp_for_each_patch(patch) patch->forced = true; } else if (klp_target_state == KLP_UNPATCHED) { klp_transition_patch->forced = true; } It looks more sane. And it makes it more clear that the special handling of KLP_UNPATCHED transition is done only when the atomic replace is not used. Otherwise, I do not see any real problem with the patch. Best Regards, Petr