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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_2 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 C074EC433FF for ; Mon, 12 Aug 2019 18:11:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7C313205F4 for ; Mon, 12 Aug 2019 18:11:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726458AbfHLSLX (ORCPT ); Mon, 12 Aug 2019 14:11:23 -0400 Received: from mail.kernel.org ([198.145.29.99]:57836 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726144AbfHLSLX (ORCPT ); Mon, 12 Aug 2019 14:11:23 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 284FA2067D; Mon, 12 Aug 2019 18:11:21 +0000 (UTC) Date: Mon, 12 Aug 2019 14:11:19 -0400 From: Steven Rostedt To: Joel Fernandes Cc: Greg Kroah-Hartman , linux-kernel@vger.kernel.org, kbuild test robot , Jonathan Corbet , Josh Triplett , Lai Jiangshan , linux-doc@vger.kernel.org, Mathieu Desnoyers , "Paul E. McKenney" , "Rafael J. Wysocki" , rcu@vger.kernel.org, Tejun Heo Subject: Re: [PATCH 3/3] driver/core: Fix build error when SRCU and lockdep disabled Message-ID: <20190812141119.6ec00a34@gandalf.local.home> In-Reply-To: <20190812130310.GA27552@google.com> References: <20190811221111.99401-1-joel@joelfernandes.org> <20190811221111.99401-3-joel@joelfernandes.org> <20190812050256.GC5834@kroah.com> <20190812130310.GA27552@google.com> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Mon, 12 Aug 2019 09:03:10 -0400 Joel Fernandes wrote: > > > drivers/base/core.c | 6 +++++- > > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/base/core.c b/drivers/base/core.c > > > index 32cf83d1c744..fe25cf690562 100644 > > > --- a/drivers/base/core.c > > > +++ b/drivers/base/core.c > > > @@ -99,7 +99,11 @@ void device_links_read_unlock(int not_used) > > > > > > int device_links_read_lock_held(void) > > > { > > > - return lock_is_held(&device_links_lock); > > > +#ifdef CONFIG_DEBUG_LOCK_ALLOC > > > + return lock_is_held(&(device_links_lock.dep_map)); > > > +#else > > > + return 1; > > > +#endif > > > > return 1? So the lock is always held? I was thinking the exact same thing. > > This is just the pattern of an assert that is disabled, so that > false-positives don't happen if lockdep is disabled. > > So say someone writes a statement like: > WARN_ON_ONCE(!device_links_read_lock_held()); > > Since lockdep is disabled, we cannot check whether lock is held or not. Yet, > we don't want false positives by reporting that the lock is not held. In this > case, it is better to report that the lock is held to suppress > false-positives. srcu_read_lock_held() also follows the same pattern. > The real answer here is to make that WARN_ON_ONCE() dependent on lockdep. Something like: some/header/file.h: #ifdef CONFIG_DEBUG_LOCK_ALLOC # define CHECK_DEVICE_LINKS_READ_LOCK_HELD() WARN_ON_ONCE(!defice_links_read_lock_held()) #else # define CHECK_DEVICE_LINKS_READ_LOCK_HELD() do { } while (0) #endif And just use CHECK_DEVICE_LINK_READ_LOCK_HELD() in those places. I agree with Greg. "device_links_read_lock_heald()" should *never* blindly return 1. It's confusing. -- Steve