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=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 470ECC4727E for ; Mon, 21 Sep 2020 23:51:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 16F1F23A6B for ; Mon, 21 Sep 2020 23:51:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728962AbgIUXvo (ORCPT ); Mon, 21 Sep 2020 19:51:44 -0400 Received: from helcar.hmeau.com ([216.24.177.18]:41180 "EHLO fornost.hmeau.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727124AbgIUXvo (ORCPT ); Mon, 21 Sep 2020 19:51:44 -0400 Received: from gwarestrin.arnor.me.apana.org.au ([192.168.0.7]) by fornost.hmeau.com with smtp (Exim 4.92 #5 (Debian)) id 1kKVaq-0007nf-Gx; Tue, 22 Sep 2020 09:51:37 +1000 Received: by gwarestrin.arnor.me.apana.org.au (sSMTP sendmail emulation); Tue, 22 Sep 2020 09:51:36 +1000 Date: Tue, 22 Sep 2020 09:51:36 +1000 From: Herbert Xu To: "Paul E. McKenney" Cc: Eric Biggers , tytso@mit.edu, linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, stable@vger.kernel.org, Linus Torvalds Subject: Re: [PATCH] random: use correct memory barriers for crng_node_pool Message-ID: <20200921235136.GA6796@gondor.apana.org.au> References: <20200916233042.51634-1-ebiggers@kernel.org> <20200917072644.GA5311@gondor.apana.org.au> <20200917165802.GC855@sol.localdomain> <20200921081939.GA4193@gondor.apana.org.au> <20200921152714.GC29330@paulmck-ThinkPad-P72> <20200921221104.GA6556@gondor.apana.org.au> <20200921232639.GK29330@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200921232639.GK29330@paulmck-ThinkPad-P72> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Mon, Sep 21, 2020 at 04:26:39PM -0700, Paul E. McKenney wrote: > > > But this reasoning could apply to any data structure that contains > > a spin lock, in particular ones that are dereferenced through RCU. > > I lost you on this one. What is special about a spin lock? I don't know, that was Eric's concern. He is inferring that spin locks through lockdep debugging may trigger dependencies that require smp_load_acquire. Anyway, my point is if it applies to crng_node_pool then it would equally apply to RCU in general. > > So my question if this reasoning is valid, then why aren't we first > > converting rcu_dereference to use smp_load_acquire? > > For LTO in ARM, rumor has it that Will is doing so. Which was what > motivated the BoF on this topic at Linux Plumbers Conference. Sure, if RCU switches over to smp_load_acquire then I would have no problems with everybody else following in its footsteps. Here is the original patch in question: https://lore.kernel.org/lkml/20200916233042.51634-1-ebiggers@kernel.org/ Cheers, -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt