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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 45E7EC43613 for ; Thu, 20 Jun 2019 09:40:55 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1BB8A2083B for ; Thu, 20 Jun 2019 09:40:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="fKXRXStK" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1BB8A2083B Authentication-Results: mail.kernel.org; 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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hdtYn-0003Mo-46; Thu, 20 Jun 2019 09:40:49 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hdtYj-0003MM-Ce for linux-arm-kernel@lists.infradead.org; Thu, 20 Jun 2019 09:40:46 +0000 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 73A51360; Thu, 20 Jun 2019 02:40:43 -0700 (PDT) Received: from [10.1.197.61] (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 331A83F246; Thu, 20 Jun 2019 02:40:42 -0700 (PDT) Subject: Re: [PATCH] genirq: Remove warning on preemptible in prepare_percpu_nmi() To: Lecopzer Chen , linux-kernel@vger.kernel.org References: <20190620091233.22731-1-lecopzer.chen@mediatek.com> From: Marc Zyngier Openpgp: preference=signencrypt Autocrypt: addr=marc.zyngier@arm.com; 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Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190620091233.22731-1-lecopzer.chen@mediatek.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190620_024045_517790_20F941AE X-CRM114-Status: GOOD ( 19.33 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Julien Thierry , Peter Zijlstra , YJ Chiang , Thomas Gleixner , Ingo Molnar , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Lecopzer, On 20/06/2019 10:12, Lecopzer Chen wrote: > prepare_percpu_nmi() acquires lock first by irq_get_desc_lock(), > no matter whether preempt enabled or not, acquiring lock forces preempt off. > > This simplifies the usage of prepare_percpu_nmi() and we don't need to > acquire extra lock or explicitly call preempt_[disable,enable](). I strongly disagree. If you're calling these functions *from* a preemptible context, you've already lost, and that's what these WARN_ON() calls are warning you about. These functions can only be called from a context that is naturally preemption free, such as a hotplug notifier. Otherwise, you have no idea which CPU you're configuring the NMI on, and I cannot see that as a good thing. Thanks, M. > > Signed-off-by: Lecopzer Chen > Cc: Thomas Gleixner > Cc: Peter Zijlstra > Cc: Ingo Molnar > Cc: Marc Zyngier > Cc: Julien Thierry > Cc: YJ Chiang > Cc: Lecopzer Chen > --- > kernel/irq/manage.c | 10 ---------- > 1 file changed, 10 deletions(-) > > diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c > index 78f3ddeb7fe4..aa03640cd7fb 100644 > --- a/kernel/irq/manage.c > +++ b/kernel/irq/manage.c > @@ -2509,9 +2509,6 @@ int request_percpu_nmi(unsigned int irq, irq_handler_t handler, > * This call prepares an interrupt line to deliver NMI on the current CPU, > * before that interrupt line gets enabled with enable_percpu_nmi(). > * > - * As a CPU local operation, this should be called from non-preemptible > - * context. > - * > * If the interrupt line cannot be used to deliver NMIs, function > * will fail returning a negative value. > */ > @@ -2521,8 +2518,6 @@ int prepare_percpu_nmi(unsigned int irq) > struct irq_desc *desc; > int ret = 0; > > - WARN_ON(preemptible()); > - > desc = irq_get_desc_lock(irq, &flags, > IRQ_GET_DESC_CHECK_PERCPU); > if (!desc) > @@ -2554,17 +2549,12 @@ int prepare_percpu_nmi(unsigned int irq) > * This call undoes the setup done by prepare_percpu_nmi(). > * > * IRQ line should not be enabled for the current CPU. > - * > - * As a CPU local operation, this should be called from non-preemptible > - * context. > */ > void teardown_percpu_nmi(unsigned int irq) > { > unsigned long flags; > struct irq_desc *desc; > > - WARN_ON(preemptible()); > - > desc = irq_get_desc_lock(irq, &flags, > IRQ_GET_DESC_CHECK_PERCPU); > if (!desc) > -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel 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=-6.7 required=3.0 tests=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 85A87C43613 for ; Thu, 20 Jun 2019 09:40:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 652EC2080C for ; Thu, 20 Jun 2019 09:40:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731103AbfFTJkp (ORCPT ); Thu, 20 Jun 2019 05:40:45 -0400 Received: from foss.arm.com ([217.140.110.172]:56426 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725925AbfFTJko (ORCPT ); Thu, 20 Jun 2019 05:40:44 -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 73A51360; Thu, 20 Jun 2019 02:40:43 -0700 (PDT) Received: from [10.1.197.61] (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 331A83F246; Thu, 20 Jun 2019 02:40:42 -0700 (PDT) Subject: Re: [PATCH] genirq: Remove warning on preemptible in prepare_percpu_nmi() To: Lecopzer Chen , linux-kernel@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org, Thomas Gleixner , Peter Zijlstra , Ingo Molnar , Julien Thierry , YJ Chiang References: <20190620091233.22731-1-lecopzer.chen@mediatek.com> From: Marc Zyngier Openpgp: preference=signencrypt Autocrypt: addr=marc.zyngier@arm.com; prefer-encrypt=mutual; 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Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190620091233.22731-1-lecopzer.chen@mediatek.com> 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 Hi Lecopzer, On 20/06/2019 10:12, Lecopzer Chen wrote: > prepare_percpu_nmi() acquires lock first by irq_get_desc_lock(), > no matter whether preempt enabled or not, acquiring lock forces preempt off. > > This simplifies the usage of prepare_percpu_nmi() and we don't need to > acquire extra lock or explicitly call preempt_[disable,enable](). I strongly disagree. If you're calling these functions *from* a preemptible context, you've already lost, and that's what these WARN_ON() calls are warning you about. These functions can only be called from a context that is naturally preemption free, such as a hotplug notifier. Otherwise, you have no idea which CPU you're configuring the NMI on, and I cannot see that as a good thing. Thanks, M. > > Signed-off-by: Lecopzer Chen > Cc: Thomas Gleixner > Cc: Peter Zijlstra > Cc: Ingo Molnar > Cc: Marc Zyngier > Cc: Julien Thierry > Cc: YJ Chiang > Cc: Lecopzer Chen > --- > kernel/irq/manage.c | 10 ---------- > 1 file changed, 10 deletions(-) > > diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c > index 78f3ddeb7fe4..aa03640cd7fb 100644 > --- a/kernel/irq/manage.c > +++ b/kernel/irq/manage.c > @@ -2509,9 +2509,6 @@ int request_percpu_nmi(unsigned int irq, irq_handler_t handler, > * This call prepares an interrupt line to deliver NMI on the current CPU, > * before that interrupt line gets enabled with enable_percpu_nmi(). > * > - * As a CPU local operation, this should be called from non-preemptible > - * context. > - * > * If the interrupt line cannot be used to deliver NMIs, function > * will fail returning a negative value. > */ > @@ -2521,8 +2518,6 @@ int prepare_percpu_nmi(unsigned int irq) > struct irq_desc *desc; > int ret = 0; > > - WARN_ON(preemptible()); > - > desc = irq_get_desc_lock(irq, &flags, > IRQ_GET_DESC_CHECK_PERCPU); > if (!desc) > @@ -2554,17 +2549,12 @@ int prepare_percpu_nmi(unsigned int irq) > * This call undoes the setup done by prepare_percpu_nmi(). > * > * IRQ line should not be enabled for the current CPU. > - * > - * As a CPU local operation, this should be called from non-preemptible > - * context. > */ > void teardown_percpu_nmi(unsigned int irq) > { > unsigned long flags; > struct irq_desc *desc; > > - WARN_ON(preemptible()); > - > desc = irq_get_desc_lock(irq, &flags, > IRQ_GET_DESC_CHECK_PERCPU); > if (!desc) > -- Jazz is not dead. It just smells funny...