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=-1.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 443FAC76195 for ; Thu, 18 Jul 2019 14:34:46 +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 192E420873 for ; Thu, 18 Jul 2019 14:34:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="SsVa55MK"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="SAx8gDCj" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 192E420873 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org 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-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:Mime-Version:References:In-Reply-To: Message-Id:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=FOcJbx1mvMmpx54E5i8iyi1O42KU9+KEqY+O4s1RLYQ=; b=SsVa55MKUmP6UQ BnIrWj8px+FNZHVjxVODa7W88TEi2uSuFo1/rZranNZUO+E3A5q6GO22q8YcjqDI/06tM6RtzfN2W rF6Y+pl76yqTPxMxp2mpH5q2eWWig7LURJ8PKZS3UQ7Licmk85chykWMw2MN7tAwpJHm3SGePGK7X dqvP3EKn+kMFwznVeUMq7m2ghJXajOumwaEA4tJrsS+Jv7Dceh4bCdaWO7nyr2D7hcRsEPBsM8noG NMThPJly/mB9H+bul2IChEVmrYHQ64xXzhO6tKE43MR+wECsit2GwiiKhRx1vBUMdUk7FNYnu+WDD nfrF1Pc91r0cKmt5B3QA==; 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 1ho7Ua-0005tH-Dt; Thu, 18 Jul 2019 14:34:44 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1ho7Rb-0003e6-DC for linux-arm-kernel@lists.infradead.org; Thu, 18 Jul 2019 14:31:42 +0000 Received: from devnote2 (ae027047.dynamic.ppp.asahi-net.or.jp [14.3.27.47]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D2D48217F4; Thu, 18 Jul 2019 14:31:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1563460296; bh=n0QuHuPmfGNDd/UjBj7iq8FnefrdHa1lz8nf16gnbDo=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=SAx8gDCjJJ1wdu+rR633sjpFn5TnWHaw0ry7jDsMkQ0OJxT3DG0n4HrAafwjAmlSv c874iRbW+O2MqL45QNl0N8V73NSlzxPS3wZtU+mLqoFvncxRhIigcgHEv16ZuA03Ug OlOMEGUQ5iEUFMYfXhfniBGHtbYlo1bWZjLa1SCk= Date: Thu, 18 Jul 2019 23:31:33 +0900 From: Masami Hiramatsu To: Mark Rutland Subject: Re: [PATCH 3/3] arm64: debug: Remove rcu_read_lock from debug exception Message-Id: <20190718233133.146065f668da6297e57e52ef@kernel.org> In-Reply-To: <20190718092022.GA3625@blommer> References: <156342860634.8565.14804606041960884732.stgit@devnote2> <156342863822.8565.7624877983728871995.stgit@devnote2> <20190718062215.GG14271@linux.ibm.com> <20190718092022.GA3625@blommer> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190718_073139_930243_4ED9B559 X-CRM114-Status: GOOD ( 13.26 ) 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: Dan Rue , Daniel Diaz , Anders Roxell , Catalin Marinas , Naresh Kamboju , Will Deacon , linux-kernel@vger.kernel.org, Masami Hiramatsu , "Paul E. McKenney" , linux-arm-kernel@lists.infradead.org, Matt Hart 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 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 [ 135.125581] 5.2.0-08445-g9187c508bdc7 #20 Not tainted [ 135.125904] ----------------------------- [ 135.126205] include/linux/rcupdate.h:594 rcu_read_lock() used illegally while idle! [ 135.126839] [ 135.126839] other info that might help us debug this: [ 135.126839] [ 135.127410] [ 135.127410] RCU used illegally from idle CPU! [ 135.127410] rcu_scheduler_active = 2, debug_locks = 1 [ 135.128114] RCU used illegally from extended quiescent state! [ 135.128555] 1 lock held by swapper/0/0: [ 135.128944] #0: (____ptrval____) (rcu_read_lock){....}, at: call_break_hook+0x0/0x178 [ 135.130499] [ 135.130499] stack backtrace: [ 135.131192] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.2.0-08445-g9187c508bdc7 #20 [ 135.131841] Hardware name: linux,dummy-virt (DT) [ 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 [ 135.136597] > > > 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? Anyway, it seems that normal irqs are also not calling irq_enter/exit except for arch/arm64/kernel/smp.c. We need to fix that too for avoiding unexpected RCU issues. Thank you, -- Masami Hiramatsu _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel