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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 A1A08C10DCE for ; Sun, 8 Mar 2020 23:25:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 837EF222C3 for ; Sun, 8 Mar 2020 23:25:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727341AbgCHXZp (ORCPT ); Sun, 8 Mar 2020 19:25:45 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:57239 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726668AbgCHXXz (ORCPT ); Sun, 8 Mar 2020 19:23:55 -0400 Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jB5Gg-00035I-LO; Mon, 09 Mar 2020 00:23:35 +0100 Received: from nanos.tec.linutronix.de (localhost [IPv6:::1]) by nanos.tec.linutronix.de (Postfix) with ESMTP id 05C631040AD; Mon, 9 Mar 2020 00:23:30 +0100 (CET) Message-Id: <20200308222609.825111830@linutronix.de> User-Agent: quilt/0.65 Date: Sun, 08 Mar 2020 23:24:08 +0100 From: Thomas Gleixner To: LKML Cc: x86@kernel.org, Steven Rostedt , Brian Gerst , Juergen Gross , Frederic Weisbecker , Alexandre Chartre Subject: [patch part-II V2 09/13] x86/entry/common: Split hardirq tracing into lockdep and ftrace parts References: <20200308222359.370649591@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 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 trace_hardirqs_off() is in fact a tracepoint which can be utilized by BPF, which is unsafe before calling enter_from_user_mode(), which in turn invokes context tracking. trace_hardirqs_off() also invokes lockdep_hardirqs_off() under the hood. OTOH lockdep needs to know about the interrupts disabled state before enter_from_user_mode(). lockdep_hardirqs_off() is safe to call at this point. Split it so lockdep knows about the state and invoke the tracepoint after the context is set straight. Even if the functions attached to a tracepoint would all be safe to be called in rcuidle having it split up is still giving a performance advantage because rcu_read_lock_sched() is avoiding the whole dance of: scru_read_lock(); rcu_irq_enter_irqson(); ... rcu_irq_exit_irqson(); scru_read_unlock(); around the tracepoint function invocation just to have the C entry points of syscalls call enter_from_user_mode() right after the above dance. Signed-off-by: Thomas Gleixner --- V2: New patch --- arch/x86/entry/common.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -60,10 +60,19 @@ static __always_inline void syscall_entr { /* * Usermode is traced as interrupts enabled, but the syscall entry - * mechanisms disable interrupts. Tell the tracer. + * mechanisms disable interrupts. Tell lockdep before calling + * enter_from_user_mode(). This is safe vs. RCU while the + * tracepoint is not. */ - trace_hardirqs_off(); + lockdep_hardirqs_on(CALLER_ADDR0); + enter_from_user_mode(); + + /* + * Tell the tracer about the irq state as well before enabling + * interrupts. + */ + __trace_hardirqs_off(); local_irq_enable(); }