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=-3.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 8CB06C35646 for ; Fri, 21 Feb 2020 13:51:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 62EB524650 for ; Fri, 21 Feb 2020 13:51:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="MEokdEKS" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729084AbgBUNv1 (ORCPT ); Fri, 21 Feb 2020 08:51:27 -0500 Received: from merlin.infradead.org ([205.233.59.134]:45508 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728777AbgBUNui (ORCPT ); Fri, 21 Feb 2020 08:50:38 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-Id:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:In-Reply-To; bh=d/0V3LhRAG1PrLn+gcCjQbXdVZCS7GcV5Q+9iS3zycc=; b=MEokdEKSO+kESf0cERiiv1bx4A n/mxBSm7Mqjo5GXINcJzIVJ6UgMKuhss0p+2u4dtf4z7J2+lgIvIOIhiaJNvn+1ZD1by8JWj2ymT5 fiIzXf5VEk2IRj0wS2Q801/FGD/YXVN5S+U4LWtCNOkzbszr5edcCgTYUQNnLVIIsv0zFODEX+jQM xB+uKPbdATDftAtHCthh3S0+6kWh3hEpLnQcl0w2hbc+4I7OGW/XyC0Y9Bj2TI/XVgeDi94IFUmgS l0Wa1kQUo8jAaFzmA2lOBL5EtqF+ia1tZ2J/2Ixd182fg6/sL2/dQ7LTp3XFZEJZ6zi+z5Ji2qbAI 7hO7H+yw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1j58gv-0006Uz-3g; Fri, 21 Feb 2020 13:50:05 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 6CCED307485; Fri, 21 Feb 2020 14:48:08 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id D1C1629B59044; Fri, 21 Feb 2020 14:50:00 +0100 (CET) Message-Id: <20200221134215.730523211@infradead.org> User-Agent: quilt/0.65 Date: Fri, 21 Feb 2020 14:34:28 +0100 From: Peter Zijlstra To: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, rostedt@goodmis.org Cc: peterz@infradead.org, mingo@kernel.org, joel@joelfernandes.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, paulmck@kernel.org, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, luto@kernel.org, tony.luck@intel.com, frederic@kernel.org, dan.carpenter@oracle.com, mhiramat@kernel.org, "Steven Rostedt (VMware)" Subject: [PATCH v4 12/27] sched,rcu,tracing: Avoid tracing before in_nmi() is correct References: <20200221133416.777099322@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If we call into a tracer 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 current code; AFAICT 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) Reviewed-by: Steven Rostedt (VMware) --- include/linux/hardirq.h | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) --- 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(); \ trace_hardirq_enter(); \ } while (0) @@ -85,7 +94,7 @@ extern void irq_exit(void); trace_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(); \