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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 4C2B5C76188 for ; Sat, 20 Jul 2019 07:32:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1FEFE2082A for ; Sat, 20 Jul 2019 07:32:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1563607962; bh=VvlwVVYw0AYiQp3KGjA3u/8HBvxH/UFD5XmZWTT+i4s=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=u+PVxcOjHdbT0aVAsVK5FjES30pdLQUC5u4UE0R8GSLBKpePgXqw9xRnXYNyP6Rim dX7BnERK6T1GIKBOcDhHSs/EEuCkiQn16f2H5pivh8n7ADgNY3aP4tMRsyQH83b8UH RbgxlLBHRJ2tsDnP+/1DFgyQOUi+HcDpe1e2ACvs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726680AbfGTHck (ORCPT ); Sat, 20 Jul 2019 03:32:40 -0400 Received: from mail.kernel.org ([198.145.29.99]:39900 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726476AbfGTHck (ORCPT ); Sat, 20 Jul 2019 03:32:40 -0400 Received: from devnote2 (72.65.214.202.bf.2iij.net [202.214.65.72]) (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 ED4C220644; Sat, 20 Jul 2019 07:32:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1563607959; bh=VvlwVVYw0AYiQp3KGjA3u/8HBvxH/UFD5XmZWTT+i4s=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=fb1SJyIYD2QW9MJU129mUeNXY672MYyi18IPneV3j3zTgNPjjNCQtyn9r3sKhBA7J vnjNvJjLQ9bbEJT5Iu+9rWu/KNKXzobh4GAKdu5PrINoLCa7WprronhuPwUB7zh0Re UExXiLJNuk3scbSB+0wmQis4dMvNjvrBF+gIXYS4= Date: Sat, 20 Jul 2019 16:32:32 +0900 From: Masami Hiramatsu To: James Morse Cc: Mark Rutland , "Paul E. McKenney" , Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Naresh Kamboju , Dan Rue , Matt Hart , Anders Roxell , Daniel Diaz Subject: Re: [PATCH 3/3] arm64: debug: Remove rcu_read_lock from debug exception Message-Id: <20190720163232.49f80bc0e53afb893e7a82e6@kernel.org> In-Reply-To: <536ba068-50de-963e-c3a7-0440da56943a@arm.com> References: <156342860634.8565.14804606041960884732.stgit@devnote2> <156342863822.8565.7624877983728871995.stgit@devnote2> <20190718062215.GG14271@linux.ibm.com> <20190718092022.GA3625@blommer> <20190718233133.146065f668da6297e57e52ef@kernel.org> <536ba068-50de-963e-c3a7-0440da56943a@arm.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi James, On Fri, 19 Jul 2019 09:42:05 +0100 James Morse wrote: > 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... OK. I think we can use rcu_nmi_enter/exit() as same as x86. > > 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. Ah, I see. Would you think we need to put rcu_nmi_enter/exit() as similar to x86 on do_mem_abort() and do_sp_pc_abort() too? Thank you, -- Masami Hiramatsu