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=-9.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 6B40DC55ABD for ; Fri, 13 Nov 2020 16:02:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 10B242076E for ; Fri, 13 Nov 2020 16:02:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726847AbgKMQCj (ORCPT ); Fri, 13 Nov 2020 11:02:39 -0500 Received: from foss.arm.com ([217.140.110.172]:40718 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726820AbgKMQCi (ORCPT ); Fri, 13 Nov 2020 11:02:38 -0500 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 0F81F1042; Fri, 13 Nov 2020 08:02:38 -0800 (PST) Received: from C02TD0UTHF1T.local (unknown [10.57.53.36]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C6A2A3F718; Fri, 13 Nov 2020 08:02:36 -0800 (PST) Date: Fri, 13 Nov 2020 16:02:34 +0000 From: Mark Rutland To: Ionela Voinescu Cc: catalin.marinas@arm.com, sudeep.holla@arm.com, will@kernel.org, morten.rasmussen@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] arm64: abort counter_read_on_cpu() when irqs_disabled() Message-ID: <20201113160234.GB44988@C02TD0UTHF1T.local> References: <20201106125334.21570-1-ionela.voinescu@arm.com> <20201113155328.4194-1-ionela.voinescu@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201113155328.4194-1-ionela.voinescu@arm.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 13, 2020 at 03:53:28PM +0000, Ionela Voinescu wrote: > Given that smp_call_function_single() can deadlock when interrupts are > disabled, abort the SMP call if irqs_disabled(). This scenario is > currently not possible given the function's uses, but safeguard this for > potential future uses. Sorry to contradict earlier feedback, but I think this is preferable as-is, since smp_call_function_single() will WARN_ON_ONCE(irqs_disabled())), but this will silently mask any dodgy usage. If we want a separate check here, I reckon we should wrap it with a WARN_ON_ONCE(), and only relax that if/when we have a legitimate case for calling this with IRQs disabled. Thanks, Mark. > > Signed-off-by: Ionela Voinescu > Cc: Catalin Marinas > Cc: Will Deacon > --- > arch/arm64/kernel/topology.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c > index 3a083a9a8ef2..e387188741f2 100644 > --- a/arch/arm64/kernel/topology.c > +++ b/arch/arm64/kernel/topology.c > @@ -343,7 +343,11 @@ static void cpu_read_constcnt(void *val) > static inline > int counters_read_on_cpu(int cpu, smp_call_func_t func, u64 *val) > { > - if (!cpu_has_amu_feat(cpu)) > + /* > + * Abort call on counterless CPU or when interrupts are > + * disabled - can lead to deadlock in smp sync call. > + */ > + if (!cpu_has_amu_feat(cpu) || unlikely(irqs_disabled())) > return -EOPNOTSUPP; > > smp_call_function_single(cpu, func, val, 1); > -- > 2.17.1 >