From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754089AbbAVWuz (ORCPT ); Thu, 22 Jan 2015 17:50:55 -0500 Received: from mail-ig0-f179.google.com ([209.85.213.179]:64412 "EHLO mail-ig0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751930AbbAVWuw (ORCPT ); Thu, 22 Jan 2015 17:50:52 -0500 Message-ID: <1421967050.3471.14.camel@edumazet-glaptop2.roam.corp.google.com> Subject: Re: [PATCH] drivers: net: xgene: fix: Out of order descriptor bytes read From: Eric Dumazet To: Iyappan Subramanian Cc: davem@davemloft.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, mlangsdo@redhat.com, patches@apm.com, Keyur Chudgar Date: Thu, 22 Jan 2015 14:50:50 -0800 In-Reply-To: <1421957007-720-1-git-send-email-isubramanian@apm.com> References: <1421957007-720-1-git-send-email-isubramanian@apm.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4-0ubuntu2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2015-01-22 at 12:03 -0800, Iyappan Subramanian wrote: > This patch fixes the following kernel crash, > > WARNING: CPU: 2 PID: 0 at net/ipv4/tcp_input.c:3079 tcp_clean_rtx_queue+0x658/0x80c() > Call trace: > > Software writes poison data into the descriptor bytes[15:8] and upon > receiving the interrupt, if those bytes are overwritten by the hardware with > the valid data, software also reads bytes[7:0] and executes receive/tx > completion logic. > > If the CPU executes the above two reads in out of order fashion, then the > bytes[7:0] will have older data and causing the kernel panic. We have to > force the order of the reads and thus this patch introduces read memory > barrier between these reads. > > Signed-off-by: Iyappan Subramanian > Signed-off-by: Keyur Chudgar > Tested-by: Mark Langsdorf > --- > drivers/net/ethernet/apm/xgene/xgene_enet_main.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/drivers/net/ethernet/apm/xgene/xgene_enet_main.c b/drivers/net/ethernet/apm/xgene/xgene_enet_main.c > index 83a5028..3622cdb 100644 > --- a/drivers/net/ethernet/apm/xgene/xgene_enet_main.c > +++ b/drivers/net/ethernet/apm/xgene/xgene_enet_main.c > @@ -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.