Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2A53BC05027 for ; Thu, 26 Jan 2023 11:52:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233517AbjAZLwh (ORCPT ); Thu, 26 Jan 2023 06:52:37 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56208 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229844AbjAZLwe (ORCPT ); Thu, 26 Jan 2023 06:52:34 -0500 Received: from outbound-smtp36.blacknight.com (outbound-smtp36.blacknight.com [46.22.139.219]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F051D3E095 for ; Thu, 26 Jan 2023 03:52:30 -0800 (PST) Received: from mail.blacknight.com (pemlinmail05.blacknight.ie [81.17.254.26]) by outbound-smtp36.blacknight.com (Postfix) with ESMTPS id 47EE51F14 for ; Thu, 26 Jan 2023 11:52:29 +0000 (GMT) Received: (qmail 32236 invoked from network); 26 Jan 2023 11:52:28 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.198.246]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 26 Jan 2023 11:52:28 -0000 Date: Thu, 26 Jan 2023 11:52:24 +0000 From: Mel Gorman To: Andrew Morton Cc: Suren Baghdasaryan , michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org, ldufour@linux.ibm.com, paulmck@kernel.org, mingo@redhat.com, will@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, jannh@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, gurua@google.com, arjunroy@google.com, soheil@google.com, hughlynch@google.com, leewalsh@google.com, posk@google.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v3 1/7] kernel/fork: convert vma assignment to a memcpy Message-ID: <20230126115224.3urhskf35eomk7xl@techsingularity.net> References: <20230125233554.153109-1-surenb@google.com> <20230125233554.153109-2-surenb@google.com> <20230125162159.a66e5ef05fecb405e85ffec9@linux-foundation.org> <20230125173449.5472cffc989dfab4b83c491d@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20230125173449.5472cffc989dfab4b83c491d@linux-foundation.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 25, 2023 at 05:34:49PM -0800, Andrew Morton wrote: > On Wed, 25 Jan 2023 16:50:01 -0800 Suren Baghdasaryan wrote: > > > On Wed, Jan 25, 2023 at 4:22 PM Andrew Morton wrote: > > > > > > On Wed, 25 Jan 2023 15:35:48 -0800 Suren Baghdasaryan wrote: > > > > > > > Convert vma assignment in vm_area_dup() to a memcpy() to prevent compiler > > > > errors when we add a const modifier to vma->vm_flags. > > > > > > > > ... > > > > > > > > --- a/kernel/fork.c > > > > +++ b/kernel/fork.c > > > > @@ -482,7 +482,7 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig) > > > > * orig->shared.rb may be modified concurrently, but the clone > > > > * will be reinitialized. > > > > */ > > > > - *new = data_race(*orig); > > > > + memcpy(new, orig, sizeof(*new)); > > > > > > The data_race() removal is unchangelogged? > > > > True. I'll add a note in the changelog about that. Ideally I would > > like to preserve it but I could not find a way to do that. > > > > Perhaps Paul can comment? > > I wonder if KCSAN knows how to detect this race, given that it's now in > a memcpy. I assume so. data_race() is just wrapping an expression around __kcsan_[en|dis]able_current and ensuring the expression is evaluated once and returning the correct type. I believe the following should be sufficient. diff --git a/kernel/fork.c b/kernel/fork.c index 9f7fe3541897..1b30ee568e02 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -472,7 +472,7 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig) * orig->shared.rb may be modified concurrently, but the clone * will be reinitialized. */ - *new = data_race(*orig); + data_race(memcpy(new, orig, sizeof(*new))); INIT_LIST_HEAD(&new->anon_vma_chain); dup_anon_vma_name(orig, new); } I don't see how memcpy could automagically figure out whether the memcpy is prone to races or not in an arbitrary context. Assuming using data_race this way is ok then Acked-by: Mel Gorman -- Mel Gorman SUSE Labs