From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755370AbdJISa5 (ORCPT ); Mon, 9 Oct 2017 14:30:57 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:33802 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754216AbdJISax (ORCPT ); Mon, 9 Oct 2017 14:30:53 -0400 From: Mark Rutland To: linux-kernel@vger.kernel.org Cc: Mark Rutland , "David S. Miller" Subject: [PATCH 08/13] net/ipv4/tcp_input.c: kill off ACCESS_ONCE() Date: Mon, 9 Oct 2017 19:28:45 +0100 Message-Id: <1507573730-8083-9-git-send-email-mark.rutland@arm.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1507573730-8083-1-git-send-email-mark.rutland@arm.com> References: <1507573730-8083-1-git-send-email-mark.rutland@arm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org For several reasons, it is desirable to use {READ,WRITE}_ONCE() in preference to ACCESS_ONCE(), and new code is expected to use one of the former. So far, there's been no reason to change most existing uses of ACCESS_ONCE(), as these aren't currently harmful. However, for some features it is necessary to instrument reads and writes separately, which is not possible with ACCESS_ONCE(). This distinction is critical to correct operation. It's possible to transform the bulk of kernel code using the Coccinelle script below. However, this doesn't handle comments, leaving references to ACCESS_ONCE() instances which have been removed. As a preparatory step, this patch converts the IPv4 TCP input code and comments to use {READ,WRITE}_ONCE() consistently. ---- virtual patch @ depends on patch @ expression E1, E2; @@ - ACCESS_ONCE(E1) = E2 + WRITE_ONCE(E1, E2) @ depends on patch @ expression E; @@ - ACCESS_ONCE(E) + READ_ONCE(E) ---- Signed-off-by: Mark Rutland Cc: David S. Miller --- net/ipv4/tcp_input.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index c5d7656..0b3bb19 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -815,12 +815,12 @@ static void tcp_update_pacing_rate(struct sock *sk) if (likely(tp->srtt_us)) do_div(rate, tp->srtt_us); - /* ACCESS_ONCE() is needed because sch_fq fetches sk_pacing_rate + /* WRITE_ONCE() is needed because sch_fq fetches sk_pacing_rate * without any lock. We want to make sure compiler wont store * intermediate values in this location. */ - ACCESS_ONCE(sk->sk_pacing_rate) = min_t(u64, rate, - sk->sk_max_pacing_rate); + WRITE_ONCE(sk->sk_pacing_rate) = min_t(u64, rate, + sk->sk_max_pacing_rate); } /* Calculate rto without backoff. This is the second half of Van Jacobson's -- 1.9.1