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=-6.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS 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 C75B1C5CFFE for ; Mon, 10 Dec 2018 14:48:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 90F932082F for ; Mon, 10 Dec 2018 14:48:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 90F932082F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728096AbeLJOsK (ORCPT ); Mon, 10 Dec 2018 09:48:10 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:55590 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726888AbeLJOsJ (ORCPT ); Mon, 10 Dec 2018 09:48:09 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2736C15AD; Mon, 10 Dec 2018 06:48:09 -0800 (PST) Received: from [10.1.196.62] (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 441273F59C; Mon, 10 Dec 2018 06:48:05 -0800 (PST) Subject: Re: [RESEND PATCH v2] clocksource/arm_arch_timer: fix a lockdep warning To: Qian Cai , akpm@linux-foundation.org Cc: mark.rutland@arm.com, daniel.lezcano@linaro.org, tglx@linutronix.de, peterz@infradead.org, mingo@kernel.org, longman@redhat.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <1543877121-4098-1-git-send-email-cai@gmx.us> <20181210135228.49751-1-cai@lca.pw> From: Marc Zyngier Openpgp: preference=signencrypt Autocrypt: addr=marc.zyngier@arm.com; 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Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1 MIME-Version: 1.0 In-Reply-To: <20181210135228.49751-1-cai@lca.pw> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/12/2018 13:52, Qian Cai wrote: > Booting this Huawei TaiShan 2280 arm64 server generated this lockdep > warning. > > [ 0.000000] lockdep_assert_cpus_held+0x50/0x60 > [ 0.000000] static_key_enable_cpuslocked+0x30/0xe8 > [ 0.000000] arch_timer_check_ool_workaround+0x128/0x2d0 > [ 0.000000] arch_timer_acpi_init+0x274/0x6ac > [ 0.000000] acpi_table_parse+0x1ac/0x218 > [ 0.000000] __acpi_probe_device_table+0x164/0x1ec > [ 0.000000] timer_probe+0x1bc/0x254 > [ 0.000000] time_init+0x44/0x98 > [ 0.000000] start_kernel+0x4ec/0x7d4 > > This is due to the commit cb538267ea1e ("jump_label/lockdep: Assert we hold > the hotplug lock for _cpuslocked() operations"). > > Since it is applying a global workaround to all CPUs here, it did not hold > any CPU locks in this path. > > arch_timer_acpi_init > arch_timer_check_ool_workaround(ate_match_acpi_oem_info, table) > arch_timer_enable_workaround(wa, local = false) > for_each_possible_cpu() > per_cpu() > > There is also another path did not have any CPU lock. > > time_init > clocksource_probe > arch_timer_of_init > arch_timer_check_ool_workaround(ate_match_dt, np) > arch_timer_enable_workaround(wa, local = false) > > When hot-adding a CPU, it will go with a slightly different route. > > arch_timer_starting_cpu > __arch_timer_setup > arch_timer_check_ool_workaround(ate_match_local_cap_id, NULL) > arch_timer_enable_workaround(wa, local = true) > __this_cpu_write() > > Hence, deal with them differently. > > Fixes: 450f9689f294 (clocksource/arm_arch_timer: Use > static_branch_enable_cpuslocked()) > Signed-off-by: Qian Cai > --- > > v2: fix the root cause instead of a workaround. > > drivers/clocksource/arm_arch_timer.c | 15 +++++++++------ > 1 file changed, 9 insertions(+), 6 deletions(-) > > diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c > index 9a7d4dc00b6e..81dca7d31d13 100644 > --- a/drivers/clocksource/arm_arch_timer.c > +++ b/drivers/clocksource/arm_arch_timer.c > @@ -492,17 +492,20 @@ void arch_timer_enable_workaround(const struct arch_timer_erratum_workaround *wa > > if (local) { > __this_cpu_write(timer_unstable_counter_workaround, wa); > + > + /* > + * Use the locked version, as we're called from the CPU > + * hotplug framework. Otherwise, we end-up in > + * deadlock-land. > + */ > + static_branch_enable_cpuslocked(&arch_timer_read_ool_enabled); I have the ugly feeling that it breaks the (equally ugly) big-little stuff where the boot CPU is affected. In this context, you'd end-up without the lock being taken and you'll get the same splat. We could start testing the CPU number, but Peter's approach seem much more palatable to me. Thanks, M. -- Jazz is not dead. It just smells funny...