From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757101AbbAZWeI (ORCPT ); Mon, 26 Jan 2015 17:34:08 -0500 Received: from shards.monkeyblade.net ([149.20.54.216]:45621 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755466AbbAZWeG (ORCPT ); Mon, 26 Jan 2015 17:34:06 -0500 Date: Mon, 26 Jan 2015 14:34:02 -0800 (PST) Message-Id: <20150126.143402.1309886104452878553.davem@davemloft.net> To: isubramanian@apm.com Cc: eric.dumazet@gmail.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, mlangsdo@redhat.com, patches@apm.com, kchudgar@apm.com Subject: Re: [PATCH] drivers: net: xgene: fix: Out of order descriptor bytes read From: David Miller In-Reply-To: References: <1421957007-720-1-git-send-email-isubramanian@apm.com> <1421967050.3471.14.camel@edumazet-glaptop2.roam.corp.google.com> X-Mailer: Mew version 6.5 on Emacs 24.1 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.7 (shards.monkeyblade.net [149.20.54.216]); Mon, 26 Jan 2015 14:34:05 -0800 (PST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Iyappan Subramanian Date: Mon, 26 Jan 2015 13:12:23 -0800 >>> @@ -369,6 +369,8 @@ static int xgene_enet_process_ring(struct xgene_enet_desc_ring *ring, >>> if (unlikely(xgene_enet_is_desc_slot_empty(raw_desc))) >>> break; >>> >>> + /* read fpqnum field after dataaddr field */ >>> + smp_rmb(); >>> if (is_rx_desc(raw_desc)) >>> ret = xgene_enet_rx_frame(ring, raw_desc); >>> else >> >> Reading your changelog, it looks like you need a plain rmb() here. > > rmb() translates into dsb, which in arm64 serializes everything > including instructions and thus expensive compared to dmb. > > Do you see any issue with smp_rmb() (which translates into dmb) ? smp_rmb() is not appropriate. You're not serializing accesses between two cpus, you're serializing the cpu with the device. From mboxrd@z Thu Jan 1 00:00:00 1970 From: davem@davemloft.net (David Miller) Date: Mon, 26 Jan 2015 14:34:02 -0800 (PST) Subject: [PATCH] drivers: net: xgene: fix: Out of order descriptor bytes read In-Reply-To: References: <1421957007-720-1-git-send-email-isubramanian@apm.com> <1421967050.3471.14.camel@edumazet-glaptop2.roam.corp.google.com> Message-ID: <20150126.143402.1309886104452878553.davem@davemloft.net> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org From: Iyappan Subramanian Date: Mon, 26 Jan 2015 13:12:23 -0800 >>> @@ -369,6 +369,8 @@ static int xgene_enet_process_ring(struct xgene_enet_desc_ring *ring, >>> if (unlikely(xgene_enet_is_desc_slot_empty(raw_desc))) >>> break; >>> >>> + /* read fpqnum field after dataaddr field */ >>> + smp_rmb(); >>> if (is_rx_desc(raw_desc)) >>> ret = xgene_enet_rx_frame(ring, raw_desc); >>> else >> >> Reading your changelog, it looks like you need a plain rmb() here. > > rmb() translates into dsb, which in arm64 serializes everything > including instructions and thus expensive compared to dmb. > > Do you see any issue with smp_rmb() (which translates into dmb) ? smp_rmb() is not appropriate. You're not serializing accesses between two cpus, you're serializing the cpu with the device.