From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH] drivers: net: xgene: fix: Out of order descriptor bytes read Date: Mon, 26 Jan 2015 13:27:32 -0800 Message-ID: <1422307652.29618.30.camel@edumazet-glaptop2.roam.corp.google.com> References: <1421957007-720-1-git-send-email-isubramanian@apm.com> <1421967050.3471.14.camel@edumazet-glaptop2.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: David Miller , netdev , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , mlangsdo@redhat.com, patches , Keyur Chudgar To: Iyappan Subramanian Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Mon, 2015-01-26 at 13:12 -0800, Iyappan Subramanian wrote: > On Thu, Jan 22, 2015 at 2:50 PM, Eric Dumazet wrote: > > 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. > > 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) ? What happens if you compile a kernel with CONFIG_SMP=n ? Most drivers in drivers/net use rmb() in this case, not smp_rmb() or barrier()