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=-11.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 21D7FC433E0 for ; Tue, 19 May 2020 19:53:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 062B920758 for ; Tue, 19 May 2020 19:53:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727973AbgESTw7 (ORCPT ); Tue, 19 May 2020 15:52:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51044 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727854AbgESTw5 (ORCPT ); Tue, 19 May 2020 15:52:57 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EECFDC08C5C0; Tue, 19 May 2020 12:52:56 -0700 (PDT) Received: from [5.158.153.53] (helo=tip-bot2.lab.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jb8Hz-0007qz-2J; Tue, 19 May 2020 21:52:35 +0200 Received: from [127.0.1.1] (localhost [IPv6:::1]) by tip-bot2.lab.linutronix.de (Postfix) with ESMTP id A41BF1C0178; Tue, 19 May 2020 21:52:34 +0200 (CEST) Date: Tue, 19 May 2020 19:52:34 -0000 From: "tip-bot2 for Peter Zijlstra" Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: core/rcu] sched,rcu,tracing: Avoid tracing before in_nmi() is correct Cc: "Steven Rostedt (VMware)" , "Peter Zijlstra (Intel)" , Thomas Gleixner , "Steven Rostedt (VMware)" , Alexandre Chartre , x86 , LKML In-Reply-To: <20200505134101.434193525@linutronix.de> References: <20200505134101.434193525@linutronix.de> MIME-Version: 1.0 Message-ID: <158991795458.17951.16867777710377461415.tip-bot2@tip-bot2> X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the core/rcu branch of tip: Commit-ID: f93524eb9c54f49be150167918f6546b0a2e09b1 Gitweb: https://git.kernel.org/tip/f93524eb9c54f49be150167918f6546b0a2e09b1 Author: Peter Zijlstra AuthorDate: Wed, 12 Feb 2020 21:01:16 +01:00 Committer: Thomas Gleixner CommitterDate: Tue, 19 May 2020 15:51:18 +02:00 sched,rcu,tracing: Avoid tracing before in_nmi() is correct If a tracer is invoked before in_nmi() becomes true, the tracer can no longer detect it is called from NMI context and behave correctly. Therefore change nmi_{enter,exit}() to use __preempt_count_{add,sub}() as the normal preempt_count_{add,sub}() have a (desired) function trace entry. This fixes a potential issue with the current code; when the function-tracer has stack-tracing enabled __trace_stack() will malfunction when it hits the preempt_count_add() function entry from NMI context. Suggested-by: Steven Rostedt (VMware) Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Thomas Gleixner Reviewed-by: Steven Rostedt (VMware) Reviewed-by: Alexandre Chartre Link: https://lkml.kernel.org/r/20200505134101.434193525@linutronix.de --- include/linux/hardirq.h | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h index a043ad8..621556e 100644 --- a/include/linux/hardirq.h +++ b/include/linux/hardirq.h @@ -66,6 +66,15 @@ extern void irq_exit(void); #endif /* + * NMI vs Tracing + * -------------- + * + * We must not land in a tracer until (or after) we've changed preempt_count + * such that in_nmi() becomes true. To that effect all NMI C entry points must + * be marked 'notrace' and call nmi_enter() as soon as possible. + */ + +/* * nmi_enter() can nest up to 15 times; see NMI_BITS. */ #define nmi_enter() \ @@ -75,7 +84,7 @@ extern void irq_exit(void); lockdep_off(); \ ftrace_nmi_enter(); \ BUG_ON(in_nmi() == NMI_MASK); \ - preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET); \ + __preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET); \ rcu_nmi_enter(); \ lockdep_hardirq_enter(); \ } while (0) @@ -85,7 +94,7 @@ extern void irq_exit(void); lockdep_hardirq_exit(); \ rcu_nmi_exit(); \ BUG_ON(!in_nmi()); \ - preempt_count_sub(NMI_OFFSET + HARDIRQ_OFFSET); \ + __preempt_count_sub(NMI_OFFSET + HARDIRQ_OFFSET); \ ftrace_nmi_exit(); \ lockdep_on(); \ printk_nmi_exit(); \