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 79143C433EF for ; Wed, 11 May 2022 08:11:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243405AbiEKILT (ORCPT ); Wed, 11 May 2022 04:11:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40498 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243409AbiEKILQ (ORCPT ); Wed, 11 May 2022 04:11:16 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 6E7DB36684; Wed, 11 May 2022 01:11:10 -0700 (PDT) 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 CB718106F; Wed, 11 May 2022 01:11:09 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.3.187]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1A9853F73D; Wed, 11 May 2022 01:11:05 -0700 (PDT) Date: Wed, 11 May 2022 09:11:02 +0100 From: Mark Rutland To: Thomas Gleixner Cc: Lukas Wunner , maz@kernel.org, Linus Walleij , Bartosz Golaszewski , linux-gpio@vger.kernel.org, Octavian Purdila , linux-kernel@vger.kernel.org, aou@eecs.berkeley.edu, catalin.marinas@arm.com, deanbo422@gmail.com, green.hu@gmail.com, guoren@kernel.org, jonas@southpole.se, kernelfans@gmail.com, linux-arm-kernel@lists.infradead.org, linux@armlinux.org.uk, palmer@dabbelt.com, paul.walmsley@sifive.com, shorne@gmail.com, stefan.kristiansson@saunalahti.fi, tsbogend@alpha.franken.de, vgupta@kernel.org, vladimir.murzin@arm.com, will@kernel.org Subject: Re: [PATCH v2 17/17] irq: remove handle_domain_{irq,nmi}() Message-ID: References: <20211026092504.27071-1-mark.rutland@arm.com> <20211026092504.27071-18-mark.rutland@arm.com> <20220506203242.GA1855@wunner.de> <20220510121320.GA3020@wunner.de> <874k1xorlj.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <874k1xorlj.ffs@tglx> Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org On Wed, May 11, 2022 at 02:11:52AM +0200, Thomas Gleixner wrote: > On Tue, May 10 2022 at 15:15, Mark Rutland wrote: > > On Tue, May 10, 2022 at 02:13:20PM +0200, Lukas Wunner wrote: > >> Actually, since you're mentioning the in_nmi() check, I suspect > >> there's another problem here: > >> > >> generic_handle_domain_nmi() warns if !in_nmi(), then calls down > >> to handle_irq_desc() which warns if !in_hardirq(). Doesn't this > >> cause a false-positive !in_hardirq() warning for a NMI on GIC/GICv3? > > > > I agree that doesn't look right. > > > >> The only driver calling request_nmi() or request_percpu_nmi() is > >> drivers/perf/arm_pmu.c. So that's the only one affected. > >> You may want to test if that driver indeed exhibits such a > >> false-positive warning since c16816acd086. > > > > In testing with v5.18-rc5, I can't see that going wrong. > > > > I also hacked the following in: > > > > -------->8-------- > > diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c > > index 939d21cd55c38..3c85608a8779f 100644 > > --- a/kernel/irq/irqdesc.c > > +++ b/kernel/irq/irqdesc.c > > @@ -718,6 +718,7 @@ EXPORT_SYMBOL_GPL(generic_handle_domain_irq); > > int generic_handle_domain_nmi(struct irq_domain *domain, unsigned int hwirq) > > { > > WARN_ON_ONCE(!in_nmi()); > > + WARN_ON_ONCE(!in_hardirq()); > > return handle_irq_desc(irq_resolve_mapping(domain, hwirq)); > > which is pointless because NMI entry code has to invoke [__]nmi_enter() > before invoking this function. [__]nmi_enter() does: > > __preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET); > > So it's more than bloody obvious why there is no warning triggered for a > regular hardware induced NMI invocation. Ugh, yes; clearly I need new eyes and/or more sleep. I entirely missed that we treat an NMI as *also* being a hardirq rather than something completely independent, and that means that this is *not* a problem for NMI. Thanks for pointing that out! > For a software invocation from the wrong context it does not matter how > many redundant WARN_ONs you add. The existing ones are covering it > nicely already. Yup; as above I was clearly not thinknig straight here. Mark.