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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 661BEC19759 for ; Thu, 1 Aug 2019 05:32:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3771E214DA for ; Thu, 1 Aug 2019 05:32:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564637554; bh=QLmvjH5tbhGx/6o/ScL4re6wjm5zhxZw6SGUDPBxV4Q=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=hrlig7NQuv5qyzFjfwzJ+Bn9i3EMpMqdVaPH3zvvwGQ1k6KN8bb1yOty65B5NXH22 PKG4OY/dlMmgBxEOAvhcFw+iUJUxcvGi7RcH8ExUEFnILhUM/uS0JOEIWjpSlZvKXq Bw5UgBx5yR5lEE6qar8DP0ATejRCQWfQXfY9OPM8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728419AbfHAFcc (ORCPT ); Thu, 1 Aug 2019 01:32:32 -0400 Received: from mail.kernel.org ([198.145.29.99]:44958 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726514AbfHAFcc (ORCPT ); Thu, 1 Aug 2019 01:32:32 -0400 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (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 7A9EC206A3; Thu, 1 Aug 2019 05:32:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564637551; bh=QLmvjH5tbhGx/6o/ScL4re6wjm5zhxZw6SGUDPBxV4Q=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=iYXXL8qCH1h7VUK+sx+0j9I5vg5cluYfgzkDF7VPdmiShGaJLBTZgR6ATdhl4EqBE hhIrnyB5t8CiJ92MUlPKi1cCoTwmvtUAg88YYA0xMDMSG0x7cO2+KjZeUAVoAvhvO+ OB3jRXcULO+gWOFtL+7SZpK4Oy7zXlG7oodXmABc= Date: Thu, 1 Aug 2019 14:32:25 +0900 From: Masami Hiramatsu To: Will Deacon Cc: Catalin Marinas , Will Deacon , Dan Rue , Daniel Diaz , Anders Roxell , Naresh Kamboju , linux-kernel@vger.kernel.org, Matt Hart , "Paul E . McKenney" , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v3 3/4] arm64: Make debug exception handlers visible from RCU Message-Id: <20190801143225.e61e38ce7a701407b19f8008@kernel.org> In-Reply-To: <20190731172602.36hdk3yb3w6uihbu@willie-the-truck> References: <156404254387.2020.886452004489353899.stgit@devnote2> <156404257493.2020.7940525305482369976.stgit@devnote2> <20190731172602.36hdk3yb3w6uihbu@willie-the-truck> 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 Will, On Wed, 31 Jul 2019 18:26:03 +0100 Will Deacon wrote: > On Thu, Jul 25, 2019 at 05:16:15PM +0900, Masami Hiramatsu wrote: > > Make debug exceptions visible from RCU so that synchronize_rcu() > > correctly track the debug exception handler. > > > > This also introduces sanity checks for user-mode exceptions as same > > as x86's ist_enter()/ist_exit(). > > > > The debug exception can interrupt in idle task. For example, it warns > > if we put a kprobe on a function called from idle task as below. > > The warning message showed that the rcu_read_lock() caused this > > problem. But actually, this means the RCU is lost the context which > > is already in NMI/IRQ. > > > > /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] > > > > So make debug exception visible to RCU can fix this warning. > > > > Reported-by: Naresh Kamboju > > Acked-by: Paul E. McKenney > > Signed-off-by: Masami Hiramatsu > > --- > > Changes in v3: > > - Make a comment for debug_exception_enter() clearer. > > --- > > arch/arm64/mm/fault.c | 40 ++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 40 insertions(+) > > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > > index 9568c116ac7f..ed6c55c87fdc 100644 > > --- a/arch/arm64/mm/fault.c > > +++ b/arch/arm64/mm/fault.c > > @@ -777,6 +777,42 @@ void __init hook_debug_fault_code(int nr, > > debug_fault_info[nr].name = name; > > } > > > > +/* > > + * In debug exception context, we explicitly disable preemption. > > Maybe add "despite having interrupts disabled"? OK, I'll add it. > > + * This serves two purposes: it makes it much less likely that we would > > + * accidentally schedule in exception context and it will force a warning > > + * if we somehow manage to schedule by accident. > > + */ > > +static void debug_exception_enter(struct pt_regs *regs) > > +{ > > + if (user_mode(regs)) { > > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); > > + } else { > > + /* > > + * We might have interrupted pretty much anything. In > > + * fact, if we're a debug exception, we can even interrupt > > + * NMI processing. We don't want this code makes in_nmi() > > + * to return true, but we need to notify RCU. > > + */ > > + rcu_nmi_enter(); > > + } > > + > > + preempt_disable(); > > If you're addingt new functions for entry/exit, maybe move the > trace_hardirqs_{on,off}() calls in here too? OK, let's move it in these functions. Thank you! > > Will -- Masami Hiramatsu