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 51C3FC433F5 for ; Tue, 8 Mar 2022 17:49:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349278AbiCHRu2 (ORCPT ); Tue, 8 Mar 2022 12:50:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43936 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1349265AbiCHRu1 (ORCPT ); Tue, 8 Mar 2022 12:50:27 -0500 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 405CA4839E; Tue, 8 Mar 2022 09:49:30 -0800 (PST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 020FC210F2; Tue, 8 Mar 2022 17:49:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1646761769; 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=COxmjuvD46AWqrnCXQNxeTDFg5Q7yCs3AfBggJx0Qfo=; b=U+6eNgQeN0cCI43ARmU3cWkQk6kq41GL/8aV8sk2+bZRhaTnj4JPyGjrYimi5PopCdm66L ObI8XeflLnnW6YHJ2CdJvHpDuTTerJ/ilp8gxK9kelgsx0ubtMQ6h0nw7lCxt/LNOXUL2c nD1OU8TlSGIGD8lMcs84HoIPeKETNEI= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1646761769; 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=COxmjuvD46AWqrnCXQNxeTDFg5Q7yCs3AfBggJx0Qfo=; b=xHXqoP0RGSvgVR51PMVKtO3/6sdVqODerDNW3M9IhT5+ed0EUV716VEDwqygOeZ0SSb2mw XT8h4Xq4iBKgytBg== Received: from pobox.suse.cz (pobox.suse.cz [10.100.2.14]) (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 9885BA3B8E; Tue, 8 Mar 2022 17:49:28 +0000 (UTC) Date: Tue, 8 Mar 2022 18:49:28 +0100 (CET) From: Miroslav Benes To: Petr Mladek cc: Chengming Zhou , jpoimboe@redhat.com, jikos@kernel.org, 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 In-Reply-To: Message-ID: References: <20220303105446.7152-1-zhouchengming@bytedance.com> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Tue, 8 Mar 2022, Petr Mladek wrote: > 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. I probably misunderstand, but the above is not generally true, is it? I mean, if the transition patch is forced during its disablement, it does not say anything about the amount of enabled patches. > 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. But it is not the same. ->replace being true only comes into play when a patch is enabled. If it is disabled, then it behaves like any other patch. So, if there is ->replace patch enabled (and it is the only patch present) and then more !->replace patches are loaded and then if ->replace patch is disabled and forced, your proposal would give a different result than what Chengming submitted, because in your case all the other patches will get ->forced set to true, while it is not the case in the original. It would be an unnecessary restriction if I am not missing something. However, I may got lost somewhere along the way. Regards Miroslav