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

[Jerin Jacob <jerinjacobk@gmail.com>]

On Wed, Mar 11, 2020 at 5:52 PM Ananyev, Konstantin
<konstantin.ananyev@intel.com> wrote:
>
>
>
> > -----Original Message-----
> > From: ZY Qiu <quzeyao@gmail.com>
> > Sent: Thursday, March 5, 2020 4:47 PM
> > To: Thomas Monjalon <thomas@monjalon.net>; Yigit, Ferruh <ferruh.yigit@intel.com>; Andrew Rybchenko <arybchenko@solarflare.com>
> > Cc: dev@dpdk.org; stephen@networkplumber.org; Ananyev, Konstantin <konstantin.ananyev@intel.com>; ZY Qiu
> > <tgw_team@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_team@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.


> >
> > +     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.ananyev@intel.com>
>
> > 2.17.1
>