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=-10.1 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,USER_AGENT_GIT 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 8438FC433FF for ; Tue, 6 Aug 2019 21:35:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 590C82089E for ; Tue, 6 Aug 2019 21:35:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1565127315; bh=tnBCKsNOXpc/So9mge9o69O10x6UKsl/NYQ+QplWqDo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=fG200dLtEM0KPI5UKNFD2GblLDlN6HOK0sneToPhkf/Y+wQkcFAcFFUD7Wb0GLkSc KbpCaEebLtZA+orx8sjoBUQhbAMwJv6yLQ9mwol1SFr5C1dESFKWXuzTuYVfjxOzG0 oMENHFnLHJAUhMnLI4v50rZt3o8DcBAMli1qXDhM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727207AbfHFVfK (ORCPT ); Tue, 6 Aug 2019 17:35:10 -0400 Received: from mail.kernel.org ([198.145.29.99]:52902 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728172AbfHFVfH (ORCPT ); Tue, 6 Aug 2019 17:35:07 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 66D96217F5; Tue, 6 Aug 2019 21:35:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1565127306; bh=tnBCKsNOXpc/So9mge9o69O10x6UKsl/NYQ+QplWqDo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=0SMu6vPLVAQdNgrK/yUVnxifbLj7RDXmrfs1PyIfJtGzPxZ/rYoJz8pDqmtvLl2ht SF4eOaPI4P1Adir3X5cGM9vMAGKy2kdSptQ/YOJWUYWNmEyXykp6MVojy5s+h0Ex1+ rrFMX7TxaZZAs6QylVjbjm4jTqYFAWZAv1odLNHo= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Masami Hiramatsu , Naresh Kamboju , "Paul E . McKenney" , Will Deacon , Sasha Levin Subject: [PATCH AUTOSEL 5.2 53/59] arm64: Make debug exception handlers visible from RCU Date: Tue, 6 Aug 2019 17:33:13 -0400 Message-Id: <20190806213319.19203-53-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190806213319.19203-1-sashal@kernel.org> References: <20190806213319.19203-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Masami Hiramatsu [ Upstream commit d8bb6718c4db9bcd075dde7ff55d46091ccfae15 ] 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 Signed-off-by: Will Deacon Signed-off-by: Sasha Levin --- arch/arm64/mm/fault.c | 57 +++++++++++++++++++++++++++++++++++++------ 1 file changed, 49 insertions(+), 8 deletions(-) diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 2d115016feb42..414b8e0f19e0e 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -800,6 +800,53 @@ void __init hook_debug_fault_code(int nr, debug_fault_info[nr].name = name; } +/* + * In debug exception context, we explicitly disable preemption despite + * having interrupts disabled. + * 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) +{ + /* + * Tell lockdep we disabled irqs in entry.S. Do nothing if they were + * already disabled to preserve the last enabled/disabled addresses. + */ + if (interrupts_enabled(regs)) + trace_hardirqs_off(); + + 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(); + + /* This code is a bit fragile. Test it. */ + RCU_LOCKDEP_WARN(!rcu_is_watching(), "exception_enter didn't work"); +} +NOKPROBE_SYMBOL(debug_exception_enter); + +static void debug_exception_exit(struct pt_regs *regs) +{ + preempt_enable_no_resched(); + + if (!user_mode(regs)) + rcu_nmi_exit(); + + if (interrupts_enabled(regs)) + trace_hardirqs_on(); +} +NOKPROBE_SYMBOL(debug_exception_exit); + #ifdef CONFIG_ARM64_ERRATUM_1463225 DECLARE_PER_CPU(int, __in_cortex_a76_erratum_1463225_wa); @@ -840,12 +887,7 @@ asmlinkage void __exception do_debug_exception(unsigned long addr_if_watchpoint, if (cortex_a76_erratum_1463225_debug_handler(regs)) return; - /* - * Tell lockdep we disabled irqs in entry.S. Do nothing if they were - * already disabled to preserve the last enabled/disabled addresses. - */ - if (interrupts_enabled(regs)) - trace_hardirqs_off(); + debug_exception_enter(regs); if (user_mode(regs) && !is_ttbr0_addr(pc)) arm64_apply_bp_hardening(); @@ -855,7 +897,6 @@ asmlinkage void __exception do_debug_exception(unsigned long addr_if_watchpoint, inf->sig, inf->code, (void __user *)pc, esr); } - if (interrupts_enabled(regs)) - trace_hardirqs_on(); + debug_exception_exit(regs); } NOKPROBE_SYMBOL(do_debug_exception); -- 2.20.1