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 A6EF7C433EF for ; Thu, 10 Mar 2022 12:58:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235231AbiCJM7D (ORCPT ); Thu, 10 Mar 2022 07:59:03 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33014 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233273AbiCJM7C (ORCPT ); Thu, 10 Mar 2022 07:59:02 -0500 Received: from mail-pj1-x1034.google.com (mail-pj1-x1034.google.com [IPv6:2607:f8b0:4864:20::1034]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0F47C4664B for ; Thu, 10 Mar 2022 04:58:01 -0800 (PST) Received: by mail-pj1-x1034.google.com with SMTP id bx5so5144490pjb.3 for ; Thu, 10 Mar 2022 04:58:01 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20210112.gappssmtp.com; s=20210112; h=message-id:date:mime-version:user-agent:subject:content-language:to :cc:references:from:in-reply-to:content-transfer-encoding; bh=ABjynNr7IG/7j/ecN/fk2K7CRcq07YcIgadt1mDYptM=; b=a/KArTwnTnLXssaJb+Fr0NDiwFJ1KPxV0OfxyDEt7Xc6jhfmBs6aDXDs1PwRCvhrm7 cCXSPqYho5kVuwb8A4y5Z7hu3ywF11gOP53H54M89PHEMpc1an3v5rvoAK3iUXTVfnkd v+yZT/3X14BvTK7t8QRw0BWrhsq1W4W8Dj+78hYvuACrq5+G2+MnbsDNXbcMEz58bQ1S dhizSBCXTav20XHYPnRdnnPKqNzurywXEM2Tc141kXrWaon5Z2YCmWoW3eEKOYePL5DQ j8fbTYQMrK8P15vGJWD7Q+5MzhewHUE2Tk+XT/dYdCQe0kqP9vITmU2Ha9lX/jLyRZE2 KmXw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=ABjynNr7IG/7j/ecN/fk2K7CRcq07YcIgadt1mDYptM=; b=O9pX60awFtUqECgjCx+cxNUecd3Ccxd6JuhxsUNoqMRuAbZumwo0inVVsbHGonD1NY A6S+qNxfyCMLFNcIvXCGl+BQfCROrDGjCgAL2kuk8rvnMQuwxFEmVHg1DaphMaKqa+Sn XbXfvCOSb02G3LrMFYLDns0RnOm9SEXIB7W7W6fKv0UqPhnESWv8k7cUCeDLFOnFl7Yy D+8v6/OLD1yMa0qRmGfX0MXUxiUzIL/Bm5qZdXjXePr05/Z41vfCYNDTotrIQ315Hqcx U/rpKprLStpbk0ASygz3fqmnU7fPLs3tYfuPjMe18ahev3ynX8RKyhDiYXKSEadVIZWA Ja1w== X-Gm-Message-State: AOAM530LVjrdrWlojwE1EtpKLdv0IYDsLE8nnBUfMHT+1ccyDS92aNrt jDl7XWkSBm3ZAImuBNv9Y0wr6w== X-Google-Smtp-Source: ABdhPJwWaI7OUB0xjsFNNyCmPiMUPkP0Z4Tg2y4MrQG2iaD6ziPzB0J+SkTkzZCndXW4irOZKsNGgA== X-Received: by 2002:a17:903:192:b0:151:8df9:6cdb with SMTP id z18-20020a170903019200b001518df96cdbmr5029952plg.20.1646917080490; Thu, 10 Mar 2022 04:58:00 -0800 (PST) Received: from [10.4.175.235] ([139.177.225.250]) by smtp.gmail.com with ESMTPSA id b2-20020a056a000a8200b004e1414f0bb1sm7701478pfl.135.2022.03.10.04.57.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 10 Mar 2022 04:58:00 -0800 (PST) Message-ID: <849e57ee-d412-30bd-3cce-47ce3362409d@bytedance.com> Date: Thu, 10 Mar 2022 20:57:54 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Thunderbird/91.6.2 Subject: Re: [External] Re: [PATCH v2] livepatch: Don't block removal of patches that are safe to unload Content-Language: en-US To: Miroslav Benes , Petr Mladek Cc: jpoimboe@redhat.com, jikos@kernel.org, joe.lawrence@redhat.com, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org References: <20220303105446.7152-1-zhouchengming@bytedance.com> From: Chengming Zhou In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org Hi, On 2022/3/9 1:49 上午, Miroslav Benes wrote: > 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. At first glance, I thought both way is right. But after looking at the case you mentioned above, they are not the same indeed. The original patch treat ->replace and not ->replace patches the same in KLP_UNPATCHED transition, and only set all patches to forced in the atomic replace transition. Thanks. > > However, I may got lost somewhere along the way. > > Regards > Miroslav