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=-8.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 6C79DC43331 for ; Tue, 31 Mar 2020 11:39:40 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id BB5B120838 for ; Tue, 31 Mar 2020 11:39:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="GwtNJliu" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BB5B120838 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-18328-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 3649 invoked by uid 550); 31 Mar 2020 11:39:21 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 7642 invoked from network); 30 Mar 2020 23:21:26 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585610475; bh=3yuZSaQ36wyLBlKdpsQHW3thBDOr3nwmhonGyIIq6BQ=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=GwtNJliugD8mSTia+pLAwHnYuw88NISnmBDSifRCYu8M8RxiQb73Rzdx2oXlg0lzF UsUIushsMgvd5Z83F9KrAsb4kNex+24c7eBETE39ZiNuNB78geEQ6t31td7mmgg5oC tuAlci+SA49SUzt802ziva3EY7/q2NZZaR6bgx3o= Date: Mon, 30 Mar 2020 16:21:14 -0700 From: "Paul E. McKenney" To: Will Deacon Cc: linux-kernel@vger.kernel.org, Eric Dumazet , Jann Horn , Kees Cook , Maddie Stone , Marco Elver , Peter Zijlstra , Thomas Gleixner , kernel-team@android.com, kernel-hardening@lists.openwall.com Subject: Re: [RFC PATCH 06/21] list: Remove superfluous WRITE_ONCE() from hlist_nulls implementation Message-ID: <20200330232114.GC19865@paulmck-ThinkPad-P72> References: <20200324153643.15527-1-will@kernel.org> <20200324153643.15527-7-will@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200324153643.15527-7-will@kernel.org> User-Agent: Mutt/1.9.4 (2018-02-28) On Tue, Mar 24, 2020 at 03:36:28PM +0000, Will Deacon wrote: > Commit 860c8802ace1 ("rcu: Use WRITE_ONCE() for assignments to ->pprev > for hlist_nulls") added WRITE_ONCE() invocations to hlist_nulls_add_head() > and hlist_nulls_del(). > > Since these functions should not ordinarily run concurrently with other > list accessors, restore the plain C assignments so that KCSAN can yell > if a data race occurs. > > Cc: Eric Dumazet > Cc: Paul E. McKenney > Cc: Peter Zijlstra > Signed-off-by: Will Deacon And this means that the lockless uses of hlist_nulls_empty() need attention, correct? Thanx, Paul > --- > include/linux/list_nulls.h | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h > index fa51a801bf32..fd154ceb5b0d 100644 > --- a/include/linux/list_nulls.h > +++ b/include/linux/list_nulls.h > @@ -80,10 +80,10 @@ static inline void hlist_nulls_add_head(struct hlist_nulls_node *n, > struct hlist_nulls_node *first = h->first; > > n->next = first; > - WRITE_ONCE(n->pprev, &h->first); > + n->pprev = &h->first; > h->first = n; > if (!is_a_nulls(first)) > - WRITE_ONCE(first->pprev, &n->next); > + first->pprev = &n->next; > } > > static inline void __hlist_nulls_del(struct hlist_nulls_node *n) > @@ -99,7 +99,7 @@ static inline void __hlist_nulls_del(struct hlist_nulls_node *n) > static inline void hlist_nulls_del(struct hlist_nulls_node *n) > { > __hlist_nulls_del(n); > - WRITE_ONCE(n->pprev, LIST_POISON2); > + n->pprev = LIST_POISON2; > } > > /** > -- > 2.20.1 >