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=-11.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 8F640C4346E for ; Thu, 24 Sep 2020 03:51:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5A1562388A for ; Thu, 24 Sep 2020 03:51:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726759AbgIXDvp (ORCPT ); Wed, 23 Sep 2020 23:51:45 -0400 Received: from foss.arm.com ([217.140.110.172]:33398 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726662AbgIXDvo (ORCPT ); Wed, 23 Sep 2020 23:51:44 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CADAC30E; Wed, 23 Sep 2020 20:51:43 -0700 (PDT) Received: from [10.163.75.147] (unknown [10.163.75.147]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 69FAF3F73B; Wed, 23 Sep 2020 20:51:40 -0700 (PDT) Subject: Re: [PATCH V3 2/3] arm64/mm/hotplug: Enable MEM_OFFLINE event handling To: Gavin Shan , linux-arm-kernel@lists.infradead.org Cc: Mark Rutland , Will Deacon , catalin.marinas@arm.com, Steve Capper , linux-kernel@vger.kernel.org, Mark Brown , Marc Zyngier , will@kernel.org References: <1600689908-28213-1-git-send-email-anshuman.khandual@arm.com> <1600689908-28213-3-git-send-email-anshuman.khandual@arm.com> From: Anshuman Khandual Message-ID: <520ea3e4-59ee-deca-3847-c57272e4fc8e@arm.com> Date: Thu, 24 Sep 2020 09:21:05 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/23/2020 12:01 PM, Gavin Shan wrote: > Hi Anshuman, > > On 9/21/20 10:05 PM, Anshuman Khandual wrote: >> This enables MEM_OFFLINE memory event handling. It will help intercept any >> possible error condition such as if boot memory some how still got offlined >> even after an explicit notifier failure, potentially by a future change in >> generic hot plug framework. This would help detect such scenarios and help >> debug further. >> >> Cc: Catalin Marinas >> Cc: Will Deacon >> Cc: Mark Rutland >> Cc: Marc Zyngier >> Cc: Steve Capper >> Cc: Mark Brown >> Cc: linux-arm-kernel@lists.infradead.org >> Cc: linux-kernel@vger.kernel.org >> Signed-off-by: Anshuman Khandual >> --- > > I'm not sure if it makes sense since MEM_OFFLINE won't be triggered > after NOTIFY_BAD is returned from MEM_GOING_OFFLINE. NOTIFY_BAD means > the whole offline process is stopped. It would be guranteed by generic > framework from syntax standpoint. Right but the intent here is to catch any deviation in generic hotplug semantics going forward. > > However, this looks good if MEM_OFFLINE is triggered without calling > into MEM_GOING_OFFLINE previously, but it would be a bug from generic > framework. Exactly, this will just ensure that we know about any change or a bug in the generic framework. But if required, this additional check can be enabled only with DEBUG_VM. > >>   arch/arm64/mm/mmu.c | 37 ++++++++++++++++++++++++++++++++----- >>   1 file changed, 32 insertions(+), 5 deletions(-) >> >> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c >> index df3b7415b128..6b171bd88bcf 100644 >> --- a/arch/arm64/mm/mmu.c >> +++ b/arch/arm64/mm/mmu.c >> @@ -1482,13 +1482,40 @@ static int prevent_bootmem_remove_notifier(struct notifier_block *nb, >>       unsigned long end_pfn = arg->start_pfn + arg->nr_pages; >>       unsigned long pfn = arg->start_pfn; >>   -    if (action != MEM_GOING_OFFLINE) >> +    if ((action != MEM_GOING_OFFLINE) && (action != MEM_OFFLINE)) >>           return NOTIFY_OK; >>   -    for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) { >> -        ms = __pfn_to_section(pfn); >> -        if (early_section(ms)) >> -            return NOTIFY_BAD; >> +    if (action == MEM_GOING_OFFLINE) { >> +        for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) { >> +            ms = __pfn_to_section(pfn); >> +            if (early_section(ms)) { >> +                pr_warn("Boot memory offlining attempted\n"); >> +                return NOTIFY_BAD; >> +            } >> +        } >> +    } else if (action == MEM_OFFLINE) { >> +        for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) { >> +            ms = __pfn_to_section(pfn); >> +            if (early_section(ms)) { >> + >> +                /* >> +                 * This should have never happened. Boot memory >> +                 * offlining should have been prevented by this >> +                 * very notifier. Probably some memory removal >> +                 * procedure might have changed which would then >> +                 * require further debug. >> +                 */ >> +                pr_err("Boot memory offlined\n"); >> + >> +                /* >> +                 * Core memory hotplug does not process a return >> +                 * code from the notifier for MEM_OFFLINE event. >> +                 * Error condition has been reported. Report as >> +                 * ignored. >> +                 */ >> +                return NOTIFY_DONE; >> +            } >> +        } >>       } >>       return NOTIFY_OK; >>   } >> > > It's pretty much irrelevant comment if the patch doesn't make sense: > the logical block for MEM_GOING_OFFLINE would be reused by MEM_OFFLINE > as they looks similar except the return value and error message :) This can be reorganized in the above mentioned format as well. Without much additional code or iteration, it might not need DEBUG_VM as well. for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) { ms = __pfn_to_section(pfn); if (!early_section(ms)) continue; if (action == MEM_GOING_OFFLINE) { pr_warn("Boot memory offlining attempted\n"); return NOTIFY_BAD; } else if (action == MEM_OFFLINE) { pr_err("Boot memory offlined\n"); return NOTIFY_DONE; } } return NOTIFY_OK;