Re: [dpdk-dev] [PATCH v3] rte_ethdev: safer memory access by calling Rx/Tx callback

[Ferruh Yigit]

On 3/11/2020 12:26 PM, Jerin Jacob wrote:

On Wed, Mar 11, 2020 at 5:52 PM Ananyev, Konstantin
<konstantin.anan...@intel.com> wrote:

-----Original Message-----
From: ZY Qiu <quze...@gmail.com>
Sent: Thursday, March 5, 2020 4:47 PM
To: Thomas Monjalon <tho...@monjalon.net>; Yigit, Ferruh <ferruh.yi...@intel.com>; 
Andrew Rybchenko <arybche...@solarflare.com>
Cc: dev@dpdk.org; step...@networkplumber.org; Ananyev, Konstantin 
<konstantin.anan...@intel.com>; ZY Qiu
<tgw_t...@tencent.com>
Subject: [PATCH v3] rte_ethdev: safer memory access by calling Rx/Tx callback

When compiling with -O0,
the compiler does not optimize two memory accesses into one.
Leads to accessing a null pointer when queue post Rx burst callback
removal while traffic is running.

Signed-off-by: ZY Qiu <tgw_t...@tencent.com>
---
  lib/librte_ethdev/rte_ethdev.h | 9 +++++----
  1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/lib/librte_ethdev/rte_ethdev.h b/lib/librte_ethdev/rte_ethdev.h
index d1a593ad1..c46612e3e 100644
--- a/lib/librte_ethdev/rte_ethdev.h
+++ b/lib/librte_ethdev/rte_ethdev.h
@@ -4388,10 +4388,10 @@ rte_eth_rx_burst(uint16_t port_id, uint16_t queue_id,
                                    rx_pkts, nb_pkts);

  #ifdef RTE_ETHDEV_RXTX_CALLBACKS
-     if (unlikely(dev->post_rx_burst_cbs[queue_id] != NULL)) {
-             struct rte_eth_rxtx_callback *cb =
-                             dev->post_rx_burst_cbs[queue_id];
+     struct rte_eth_rxtx_callback *volatile cb =
+                     dev->post_rx_burst_cbs[queue_id];

I prefer to change to compiler_barrier() if it working as volatile may have a
performance impact on fast-path code.

Hi ZY Qiu,

Did you able to test with compiler barrier, is it solving your problem?

If there is no update on the issue, I will mark it as rejected.

Thanks,
ferruh

+     if (unlikely(cb != NULL)) {
               do {
                       nb_rx = cb->fn.rx(port_id, queue_id, rx_pkts, nb_rx,
                                               nb_pkts, cb->param);
@@ -4652,7 +4652,8 @@ rte_eth_tx_burst(uint16_t port_id, uint16_t queue_id,
  #endif

  #ifdef RTE_ETHDEV_RXTX_CALLBACKS
-     struct rte_eth_rxtx_callback *cb = dev->pre_tx_burst_cbs[queue_id];
+     struct rte_eth_rxtx_callback *volatile cb =
+                     dev->pre_tx_burst_cbs[queue_id];

       if (unlikely(cb != NULL)) {
               do {
--

Acked-by: Konstantin Ananyev <konstantin.anan...@intel.com>

2.17.1