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=-5.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 85229C742BD for ; Fri, 12 Jul 2019 15:11:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5B7F62166E for ; Fri, 12 Jul 2019 15:11:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="xyHw0p49" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727060AbfGLPKy (ORCPT ); Fri, 12 Jul 2019 11:10:54 -0400 Received: from mail-pl1-f195.google.com ([209.85.214.195]:33474 "EHLO mail-pl1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726939AbfGLPKy (ORCPT ); Fri, 12 Jul 2019 11:10:54 -0400 Received: by mail-pl1-f195.google.com with SMTP id c14so4908584plo.0 for ; Fri, 12 Jul 2019 08:10:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=bpkdGumnCxVJ5QkvopMAKHuDk2Cmi1QHk5zgDoY3xmE=; b=xyHw0p49aGG+bHJkAwOFsAyVLIy6ynGQUOVqJSZW2rdYBcMge9BS0dv8b3pXcc+QsB 52ZjWyLo4eCKwwXkK1MywW+/ICPskgQBpOWaqdYt311VFlay/UvS+NI+iDdRBDC8nfQH 7iG2DsYxsndMDH8pWwOufpGY4o74/6StEFO8o= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=bpkdGumnCxVJ5QkvopMAKHuDk2Cmi1QHk5zgDoY3xmE=; b=Ppvx0H+ZKv0IhpWTY7fUXxmmWFYCUMkNEW9ZnvS3A/7xU2m0p8YeHYS/1xKLpdDvhr /10A0de336MZ/ys87ZQcHNpn0cuk5KCrHCsUeX3PUo17mydVCE1BMDz9D+nz/R4lBVuI Pb0o70EUu6ndwXhcVqqMHfZnB6JNfV6buchlsFURDni2fWtHOm1SZuJDoVx1UdmcJiNf 0bUZi5jHIedh8pbYmFfcDyo0O6qNzCyLxVXP4speUuzwaxn548X+1BGznQxZ1O6M5Idn cmDvKH2X4pHU3yuDPgNll5CJO2L56F5w0P/DIgQheo09RdI8362KmUsRNDwfFB1RoHLd ZHkg== X-Gm-Message-State: APjAAAV9LofttVlUHe3RfenFLpOulqmFvgggiIUWkAeukYdoh0GM3l2H OiDRblgE4Na3Ns8T2p4h91o= X-Google-Smtp-Source: APXvYqxJ7Kem+nQt02Z16GBq/vs2O/YsBJDeceBJIv6amPGaj5XayXNv7u5mL3pmC3eI8AkB/Vv2gw== X-Received: by 2002:a17:902:6a88:: with SMTP id n8mr12077228plk.70.1562944253560; Fri, 12 Jul 2019 08:10:53 -0700 (PDT) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id l124sm8863171pgl.54.2019.07.12.08.10.52 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Fri, 12 Jul 2019 08:10:52 -0700 (PDT) Date: Fri, 12 Jul 2019 11:10:51 -0400 From: Joel Fernandes To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Alexey Kuznetsov , Bjorn Helgaas , Borislav Petkov , c0d1n61at3@gmail.com, "David S. Miller" , edumazet@google.com, Greg Kroah-Hartman , Hideaki YOSHIFUJI , "H. Peter Anvin" , Ingo Molnar , Josh Triplett , keescook@chromium.org, kernel-hardening@lists.openwall.com, Lai Jiangshan , Len Brown , linux-acpi@vger.kernel.org, linux-pci@vger.kernel.org, linux-pm@vger.kernel.org, Mathieu Desnoyers , neilb@suse.com, netdev@vger.kernel.org, oleg@redhat.com, "Paul E. McKenney" , Pavel Machek , "Rafael J. Wysocki" , Rasmus Villemoes , rcu@vger.kernel.org, Steven Rostedt , Tejun Heo , Thomas Gleixner , will@kernel.org, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" Subject: Re: [PATCH v1 1/6] rcu: Add support for consolidated-RCU reader checking Message-ID: <20190712151051.GB235410@google.com> References: <20190711234401.220336-1-joel@joelfernandes.org> <20190711234401.220336-2-joel@joelfernandes.org> <20190712111125.GT3402@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190712111125.GT3402@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Fri, Jul 12, 2019 at 01:11:25PM +0200, Peter Zijlstra wrote: > On Thu, Jul 11, 2019 at 07:43:56PM -0400, Joel Fernandes (Google) wrote: > > +int rcu_read_lock_any_held(void) > > +{ > > + int lockdep_opinion = 0; > > + > > + if (!debug_lockdep_rcu_enabled()) > > + return 1; > > + if (!rcu_is_watching()) > > + return 0; > > + if (!rcu_lockdep_current_cpu_online()) > > + return 0; > > + > > + /* Preemptible RCU flavor */ > > + if (lock_is_held(&rcu_lock_map)) > > you forgot debug_locks here. Actually, it turns out debug_locks checking is not even needed. If debug_locks == 0, then debug_lockdep_rcu_enabled() returns 0 and we would not get to this point. > > + return 1; > > + > > + /* BH flavor */ > > + if (in_softirq() || irqs_disabled()) > > I'm not sure I'd put irqs_disabled() under BH, also this entire > condition is superfluous, see below. > > > + return 1; > > + > > + /* Sched flavor */ > > + if (debug_locks) > > + lockdep_opinion = lock_is_held(&rcu_sched_lock_map); > > + return lockdep_opinion || !preemptible(); > > that !preemptible() turns into: > > !(preempt_count()==0 && !irqs_disabled()) > > which is: > > preempt_count() != 0 || irqs_disabled() > > and already includes irqs_disabled() and in_softirq(). > > > +} > > So maybe something lke: > > if (debug_locks && (lock_is_held(&rcu_lock_map) || > lock_is_held(&rcu_sched_lock_map))) > return true; Agreed, I will do it this way (without the debug_locks) like: ---8<----------------------- diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index ba861d1716d3..339aebc330db 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -296,27 +296,15 @@ EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); int rcu_read_lock_any_held(void) { - int lockdep_opinion = 0; - if (!debug_lockdep_rcu_enabled()) return 1; if (!rcu_is_watching()) return 0; if (!rcu_lockdep_current_cpu_online()) return 0; - - /* Preemptible RCU flavor */ - if (lock_is_held(&rcu_lock_map)) - return 1; - - /* BH flavor */ - if (in_softirq() || irqs_disabled()) - return 1; - - /* Sched flavor */ - if (debug_locks) - lockdep_opinion = lock_is_held(&rcu_sched_lock_map); - return lockdep_opinion || !preemptible(); + if (lock_is_held(&rcu_lock_map) || lock_is_held(&rcu_sched_lock_map)) + return 1; + return !preemptible(); } EXPORT_SYMBOL_GPL(rcu_read_lock_any_held);