From ecf6ba83d76e0c78e89401750dc527008e14faa2 Mon Sep 17 00:00:00 2001 From: Iyappan Subramanian Date: Thu, 29 Jan 2015 14:38:23 -0800 Subject: [PATCH] drivers: net: xgene: fix: Out of order descriptor bytes read 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: [] dump_backtrace+0x0/0x184 [] show_stack+0x10/0x1c [] dump_stack+0x74/0x98 [] warn_slowpath_common+0x88/0xb0 [] warn_slowpath_null+0x14/0x20 [] tcp_clean_rtx_queue+0x654/0x80c [] tcp_ack+0x454/0x688 [] tcp_rcv_established+0x4a4/0x62c [] tcp_v4_do_rcv+0x16c/0x350 [] tcp_v4_rcv+0x8e8/0x904 [] ip_local_deliver_finish+0x100/0x26c [] ip_local_deliver+0xac/0xc4 [] ip_rcv_finish+0xe8/0x328 [] ip_rcv+0x24c/0x38c [] __netif_receive_skb_core+0x29c/0x7c8 [] __netif_receive_skb+0x28/0x7c [] netif_receive_skb_internal+0x5c/0xe0 [] napi_gro_receive+0xb4/0x110 [] xgene_enet_process_ring+0x144/0x338 [] xgene_enet_napi+0x1c/0x50 [] net_rx_action+0x154/0x228 [] __do_softirq+0x110/0x28c [] irq_exit+0x8c/0xc0 [] handle_IRQ+0x44/0xa8 [] gic_handle_irq+0x38/0x7c [...] 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 Signed-off-by: David S. Miller --- 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 83a50280bb70..793f3b73eeff 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 */ + dma_rmb(); if (is_rx_desc(raw_desc)) ret = xgene_enet_rx_frame(ring, raw_desc); else -- 2.34.1