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=-2.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 741D1C76188 for ; Fri, 19 Jul 2019 08:42:28 +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 3AD1821850 for ; Fri, 19 Jul 2019 08:42:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Xu73C0FC" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3AD1821850 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-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=PAeotJ7TIl6824c/83yh0vUEkA46TdA7RqnEGfVvUdA=; b=Xu73C0FCs1AJM2+nNaUYPInDP VPpUbNZ7Ha/+KuCdqeu1FnCzW53U5M+LyHVoaqZpnzc8f/0ti4zJylQyU0adE661Xm3g1YhEWfbfW brvzPMVtaqntbBCjwKDGpax7PIxU7QEex59gggvUh69Jkt3r2lyQQsdqMUE4O5YKS+HR2/tUZOiPn 3zVktQ6GzWA0txOzggHX5LEHxvjUXuu6vHLMW8IkW7ByxTXru84OO2YqUEI8kK4N9LW2URKEB8Fdt VXz1P4syHClKiJemXyxMSlg2x3+pdt6Fq4b4noKe/FkPWT8udtsHQKKBM4sSBmhjMdjWZoZXKnTNo dZLyia4bQ==; 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 1hoOTC-0006g1-Nz; Fri, 19 Jul 2019 08:42:26 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hoOT8-0006c8-3L for linux-arm-kernel@lists.infradead.org; Fri, 19 Jul 2019 08:42:23 +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 BCF95337; Fri, 19 Jul 2019 01:42:18 -0700 (PDT) Received: from [10.1.36.145] (c02yf087jhd5.cambridge.arm.com [10.1.36.145]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1E19E3F71A; Fri, 19 Jul 2019 01:42:16 -0700 (PDT) Subject: Re: [PATCH 3/3] arm64: debug: Remove rcu_read_lock from debug exception To: Masami Hiramatsu References: <156342860634.8565.14804606041960884732.stgit@devnote2> <156342863822.8565.7624877983728871995.stgit@devnote2> <20190718062215.GG14271@linux.ibm.com> <20190718092022.GA3625@blommer> <20190718233133.146065f668da6297e57e52ef@kernel.org> From: James Morse Message-ID: <536ba068-50de-963e-c3a7-0440da56943a@arm.com> Date: Fri, 19 Jul 2019 09:42:05 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190718233133.146065f668da6297e57e52ef@kernel.org> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190719_014222_190243_7459CE41 X-CRM114-Status: GOOD ( 16.39 ) 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: Mark Rutland , Dan Rue , Daniel Diaz , Anders Roxell , Catalin Marinas , Naresh Kamboju , Will Deacon , linux-kernel@vger.kernel.org, Matt Hart , "Paul E. McKenney" , linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi, On 7/18/19 3:31 PM, Masami Hiramatsu wrote: > On Thu, 18 Jul 2019 10:20:23 +0100 > Mark Rutland wrote: > >> On Wed, Jul 17, 2019 at 11:22:15PM -0700, Paul E. McKenney wrote: >>> On Thu, Jul 18, 2019 at 02:43:58PM +0900, Masami Hiramatsu wrote: >>>> Remove rcu_read_lock()/rcu_read_unlock() from debug exception >>>> handlers since the software breakpoint can be hit on idle task. >> >> Why precisely do we need to elide these? Are we seeing warnings today? > > Yes, unfortunately, or fortunately. Naresh reported that warns when > ftracetest ran. I confirmed that happens if I probe on default_idle_call too. > > /sys/kernel/debug/tracing # echo p default_idle_call >> kprobe_events > /sys/kernel/debug/tracing # echo 1 > events/kprobes/enable > /sys/kernel/debug/tracing # [ 135.122237] > [ 135.125035] ============================= > [ 135.125310] WARNING: suspicious RCU usage > [ 135.132224] Call trace: > [ 135.132491] dump_backtrace+0x0/0x140 > [ 135.132806] show_stack+0x24/0x30 > [ 135.133133] dump_stack+0xc4/0x10c > [ 135.133726] lockdep_rcu_suspicious+0xf8/0x108 > [ 135.134171] call_break_hook+0x170/0x178 > [ 135.134486] brk_handler+0x28/0x68 > [ 135.134792] do_debug_exception+0x90/0x150 > [ 135.135051] el1_dbg+0x18/0x8c > [ 135.135260] default_idle_call+0x0/0x44 > [ 135.135516] cpu_startup_entry+0x2c/0x30 > [ 135.135815] rest_init+0x1b0/0x280 > [ 135.136044] arch_call_rest_init+0x14/0x1c > [ 135.136305] start_kernel+0x4d4/0x500 >>> The exception entry and exit use irq_enter() and irq_exit(), in this >>> case, correct? Otherwise RCU will be ignoring this CPU. >> >> This is missing today, which sounds like the underlying bug. > > Agreed. I'm not so familier with how debug exception is handled on arm64, > would it be a kind of NMI or IRQ? Debug exceptions can interrupt both SError (think: machine check) and pseudo-NMI, which both in turn interrupt interrupt-masked code. So they are a kind of NMI. But, be careful not to call 'nmi_enter()' twice, see do_serror() for how we work around this... > Anyway, it seems that normal irqs are also not calling irq_enter/exit > except for arch/arm64/kernel/smp.c drivers/irqchip/irq-gic.c:gic_handle_irq() either calls handle_domain_irq() or handle_IPI(). The enter/exit calls live in those functions. Thanks, James _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel