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=-8.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT 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 03E78C072B5 for ; Fri, 24 May 2019 17:03:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B6B802186A for ; Fri, 24 May 2019 17:03:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=amarulasolutions.com header.i=@amarulasolutions.com header.b="UtzECo6J" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391326AbfEXRDk (ORCPT ); Fri, 24 May 2019 13:03:40 -0400 Received: from mail-wr1-f68.google.com ([209.85.221.68]:41934 "EHLO mail-wr1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390960AbfEXRDj (ORCPT ); Fri, 24 May 2019 13:03:39 -0400 Received: by mail-wr1-f68.google.com with SMTP id u16so6832009wrn.8 for ; Fri, 24 May 2019 10:03:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amarulasolutions.com; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=vlDKP+ImHY8gEo+CL/pDlFa1l6Ab1OQoJ+zrGXUdEuQ=; b=UtzECo6Jq5+8H/lMh3ZOFl3Dib0EkSEEtBomTPpK0P2vtMkt99iYEGeHzpCRlDxkR3 E+aDnO+P7ia9y2hoCdvqqKzf09CgsZ+JPHqOU6AIuFWUQrEa0GtN9ubFAjN1wAeKQtKm 64EGLy8CuPDsShjCVYyy+vsNPH3QNGJHklAAA= 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=vlDKP+ImHY8gEo+CL/pDlFa1l6Ab1OQoJ+zrGXUdEuQ=; b=KS1GlAnYYNQg3O54GDmOBcC/uNg9Fz1Ewkim+I/T+Tu5f1ZVjH3aN4qMVN3irnv3r3 AlIH3foXerkArwep6vQoasr7Ns/MXH+AUVwishEIUQ48cYLr+bDz2in5Fv38Zs6lw7yT 3rnP/SlxIUmCOpixEudgM8UkaNLNcudRdUAncF8uFe0yMD8JCommz0Xl9I1ozxWgFX11 3ckvp/A1VZvy0Jic3Hh92gp0AzCZtUddtKgL3HrDjVdgdeDQq05rtVxYCBloEP8unlmI 4WXJ6rcp7w6P7OJfWweQmkof5rhqJzqM1t+s8RNQhdRlGtDVmae2N41hKCWqK9m75H30 whAg== X-Gm-Message-State: APjAAAW2yHGucIxvtba2/4h96ppDuKq27CTRkRUw3kXxyrpE2+Aak2z4 q2yL49s/0wIHUcgIy55s3ZO/Hg== X-Google-Smtp-Source: APXvYqyuTG315nDS22Lscxx6ZIBoD+gT5JkjezYbuU5OMnDLFpUBOCyFyecPTIzX9NbLTgx81em1YA== X-Received: by 2002:adf:f909:: with SMTP id b9mr21671891wrr.119.1558717417618; Fri, 24 May 2019 10:03:37 -0700 (PDT) Received: from andrea ([89.22.71.151]) by smtp.gmail.com with ESMTPSA id r4sm1928306wrv.34.2019.05.24.10.03.36 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 24 May 2019 10:03:37 -0700 (PDT) Date: Fri, 24 May 2019 19:03:28 +0200 From: Andrea Parri To: Joel Fernandes Cc: linux-kernel@vger.kernel.org, "Paul E. McKenney" , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , rcu@vger.kernel.org, Peter Zijlstra , Will Deacon , Mark Rutland , Matthew Wilcox , Sasha Levin Subject: Re: [PATCH] rcu: Prevent evaluation of rcu_assign_pointer() Message-ID: <20190524170328.GA7540@andrea> References: <1558694197-19295-1-git-send-email-andrea.parri@amarulasolutions.com> <20190524164509.GA197789@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190524164509.GA197789@google.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 24, 2019 at 12:45:09PM -0400, Joel Fernandes wrote: > On Fri, May 24, 2019 at 12:36:37PM +0200, Andrea Parri wrote: > > Quoting Paul [1]: > > > > "Given that a quick (and perhaps error-prone) search of the uses > > of rcu_assign_pointer() in v5.1 didn't find a single use of the > > return value, let's please instead change the documentation and > > implementation to eliminate the return value." > > > > [1] https://lkml.kernel.org/r/20190523135013.GL28207@linux.ibm.com > > > > Signed-off-by: Andrea Parri > > Cc: "Paul E. McKenney" > > Cc: Josh Triplett > > Cc: Steven Rostedt > > Cc: Mathieu Desnoyers > > Cc: Lai Jiangshan > > Cc: Joel Fernandes > > Cc: rcu@vger.kernel.org > > Cc: Peter Zijlstra > > Cc: Will Deacon > > Cc: Mark Rutland > > Cc: Matthew Wilcox > > Cc: Sasha Levin > > --- > > Matthew, Sasha: > > > > The patch is based on -rcu/dev; I took the liberty of applying the > > same change to your #defines in: > > > > tools/testing/radix-tree/linux/rcupdate.h > > tools/include/linux/rcu.h > > > > but I admit that I'm not familiar with their uses: please shout if > > you have any objections with it. > > --- > > Documentation/RCU/whatisRCU.txt | 8 ++++---- > > include/linux/rcupdate.h | 5 ++--- > > tools/include/linux/rcu.h | 11 +++++++++-- > > tools/testing/radix-tree/linux/rcupdate.h | 5 ++++- > > 4 files changed, 19 insertions(+), 10 deletions(-) > > > > diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt > > index 981651a8b65d2..f99a87b9a88fa 100644 > > --- a/Documentation/RCU/whatisRCU.txt > > +++ b/Documentation/RCU/whatisRCU.txt > > @@ -212,7 +212,7 @@ synchronize_rcu() > > > > rcu_assign_pointer() > > > > - typeof(p) rcu_assign_pointer(p, typeof(p) v); > > + rcu_assign_pointer(p, typeof(p) v); > > > > Yes, rcu_assign_pointer() -is- implemented as a macro, though it > > would be cool to be able to declare a function in this manner. > > @@ -220,9 +220,9 @@ rcu_assign_pointer() > > > > The updater uses this function to assign a new value to an > > RCU-protected pointer, in order to safely communicate the change > > - in value from the updater to the reader. This function returns > > - the new value, and also executes any memory-barrier instructions > > - required for a given CPU architecture. > > + in value from the updater to the reader. This macro does not > > + evaluate to an rvalue, but it does execute any memory-barrier > > + instructions required for a given CPU architecture. > > > > Perhaps just as important, it serves to document (1) which > > pointers are protected by RCU and (2) the point at which a > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index 915460ec08722..a5f61a08e65fc 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -367,7 +367,7 @@ static inline void rcu_preempt_sleep_check(void) { } > > * other macros that it invokes. > > */ > > #define rcu_assign_pointer(p, v) \ > > -({ \ > > +do { \ > > uintptr_t _r_a_p__v = (uintptr_t)(v); \ > > rcu_check_sparse(p, __rcu); \ > > \ > > @@ -375,8 +375,7 @@ static inline void rcu_preempt_sleep_check(void) { } > > WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \ > > else \ > > smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \ > > - _r_a_p__v; \ > > -}) > > +} while (0) > > > > /** > > * rcu_swap_protected() - swap an RCU and a regular pointer > > diff --git a/tools/include/linux/rcu.h b/tools/include/linux/rcu.h > > index 7d02527e5bcea..01a435ee48cd6 100644 > > --- a/tools/include/linux/rcu.h > > +++ b/tools/include/linux/rcu.h > > @@ -19,7 +19,14 @@ static inline bool rcu_is_watching(void) > > return false; > > } > > > > -#define rcu_assign_pointer(p, v) ((p) = (v)) > > -#define RCU_INIT_POINTER(p, v) p=(v) > > +#define rcu_assign_pointer(p, v) \ > > +do { \ > > + (p) = (v); \ > > +} while (0) > > + > > +#define RCU_INIT_POINTER(p, v) \ > > +do { \ > > + (p) = (v); \ > > +} while (0) > > > > #endif > > diff --git a/tools/testing/radix-tree/linux/rcupdate.h b/tools/testing/radix-tree/linux/rcupdate.h > > index fd280b070fdb1..48212f3a758e6 100644 > > --- a/tools/testing/radix-tree/linux/rcupdate.h > > +++ b/tools/testing/radix-tree/linux/rcupdate.h > > @@ -7,6 +7,9 @@ > > #define rcu_dereference_raw(p) rcu_dereference(p) > > #define rcu_dereference_protected(p, cond) rcu_dereference(p) > > #define rcu_dereference_check(p, cond) rcu_dereference(p) > > -#define RCU_INIT_POINTER(p, v) (p) = (v) > > +#define RCU_INIT_POINTER(p, v) \ > > +do { \ > > + (p) = (v); \ > > +} while (0) > > > > #endif > > -- > > 2.7.4 > > > > Other than Paul's nits, LGTM. Thanks. Thank you, Joel! Will fix those and resend, most likely next week. Andrea