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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 090B2C433F5 for ; Fri, 24 Sep 2021 17:36:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D502F61250 for ; Fri, 24 Sep 2021 17:36:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344445AbhIXRiD (ORCPT ); Fri, 24 Sep 2021 13:38:03 -0400 Received: from foss.arm.com ([217.140.110.172]:52298 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241912AbhIXRiA (ORCPT ); Fri, 24 Sep 2021 13:38:00 -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 58FD2D6E; Fri, 24 Sep 2021 10:36:24 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.20.95]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2542C3F59C; Fri, 24 Sep 2021 10:36:21 -0700 (PDT) Date: Fri, 24 Sep 2021 18:36:15 +0100 From: Mark Rutland To: Pingfan Liu , Thomas Gleixner , "Paul E. McKenney" Cc: linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon , Marc Zyngier , Joey Gouly , Sami Tolvanen , Julien Thierry , Yuichi Ito , linux-kernel@vger.kernel.org, Sven Schnelle , Vasily Gorbik Subject: Re: [PATCHv2 0/5] arm64/irqentry: remove duplicate housekeeping of Message-ID: <20210924173615.GA42068@C02TD0UTHF1T.local> References: <20210924132837.45994-1-kernelfans@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210924132837.45994-1-kernelfans@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [Adding Paul for RCU, s390 folk for entry code RCU semantics] On Fri, Sep 24, 2021 at 09:28:32PM +0800, Pingfan Liu wrote: > After introducing arm64/kernel/entry_common.c which is akin to > kernel/entry/common.c , the housekeeping of rcu/trace are done twice as > the following: > enter_from_kernel_mode()->rcu_irq_enter(). > And > gic_handle_irq()->...->handle_domain_irq()->irq_enter()->rcu_irq_enter() > > Besides redundance, based on code analysis, the redundance also raise > some mistake, e.g. rcu_data->dynticks_nmi_nesting inc 2, which causes > rcu_is_cpu_rrupt_from_idle() unexpected. Hmmm... The fundamental questionss are: 1) Who is supposed to be responsible for doing the rcu entry/exit? 2) Is it supposed to matter if this happens multiple times? For (1), I'd generally expect that this is supposed to happen in the arch/common entry code, since that itself (or the irqchip driver) could depend on RCU, and if that's the case thatn handle_domain_irq() shouldn't need to call rcu_irq_enter(). That would be consistent with the way we handle all other exceptions. For (2) I don't know whether the level of nesting is suppoosed to matter. I was under the impression it wasn't meant to matter in general, so I'm a little surprised that rcu_is_cpu_rrupt_from_idle() depends on a specific level of nesting. >From a glance it looks like this would cause rcu_sched_clock_irq() to skip setting TIF_NEED_RESCHED, and to not call invoke_rcu_core(), which doesn't sound right, at least... Thomas, Paul, thoughts? AFAICT, s390 will have a similar flow on its IRQ handling path, so if this is a real issue they'll be affected too. Thanks, Mark. > Nmi also faces duplicate accounts. This series aims to address these > duplicate issues. > [1-2/5]: address nmi account duplicate > [3-4/5]: address rcu housekeeping duplicate in irq > [5/5]: as a natural result of [3-4/5], address a history issue. [1] > > > History: > v1 -> v2: > change the subject as the motivation varies. > add the fix for nmi account duplicate > > The subject of v1 is "[PATCH 1/3] kernel/irq: __handle_domain_irq() > makes irq_enter/exit arch optional". [2] It is brought up to fix [1]. > > There have been some tries to enable crash-stop-NMI on arm64, one by me, > the other by Yuichi's [4]. I hope after this series, they can advance, > as Marc said in [3] "No additional NMI patches will make it until we > have resolved the issues" > > [1] https://lore.kernel.org/linux-arm-kernel/87lfewnmdz.fsf@nanos.tec.linutronix.de/ > [2] https://lore.kernel.org/linux-arm-kernel/1607912752-12481-1-git-send-email-kernelfans@gmail.com > [3] https://lore.kernel.org/linux-arm-kernel/afd82be798cb55fd2f96940db7be78c0@kernel.org > [4] https://lore.kernel.org/linux-arm-kernel/20201104080539.3205889-1-ito-yuichi@fujitsu.com > > Cc: Catalin Marinas > Cc: Will Deacon > Cc: Mark Rutland > Cc: Marc Zyngier > Cc: Joey Gouly > Cc: Sami Tolvanen > Cc: Julien Thierry > Cc: Thomas Gleixner > Cc: Yuichi Ito > Cc: linux-kernel@vger.kernel.org > To: linux-arm-kernel@lists.infradead.org > > > Pingfan Liu (5): > arm64/entry-common: push the judgement of nmi ahead > irqchip/GICv3: expose handle_nmi() directly > kernel/irq: make irq_{enter,exit}() in handle_domain_irq() arch > optional > irqchip/GICv3: let gic_handle_irq() utilize irqentry on arm64 > irqchip/GICv3: make reschedule-ipi light weight > > arch/arm64/Kconfig | 1 + > arch/arm64/include/asm/irq.h | 7 ++++ > arch/arm64/kernel/entry-common.c | 45 +++++++++++++++------- > arch/arm64/kernel/irq.c | 29 ++++++++++++++ > drivers/irqchip/irq-gic-v3.c | 66 ++++++++++++++++++++------------ > kernel/irq/Kconfig | 3 ++ > kernel/irq/irqdesc.c | 4 ++ > 7 files changed, 116 insertions(+), 39 deletions(-) > > -- > 2.31.1 >