[Bug 882] ixgbe dirver may resue some unreleased mbufs

[bugzilla@dpdk.org]

https://bugs.dpdk.org/show_bug.cgi?id=882

            Bug ID: 882
           Summary: ixgbe dirver may resue some unreleased mbufs
           Product: DPDK
           Version: 20.11
          Hardware: x86
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: ethdev
          Assignee: dev@dpdk.org
          Reporter: zhengbin.89740@bytedance.com
  Target Milestone: ---

Created attachment 174
  --> https://bugs.dpdk.org/attachment.cgi?id=174&action=edit
this demo can reproduce this bug

file: drivers/net/ixgbe/ixgbe_rxtx_vec_sse.c:334
func: _recv_raw_pkts_vec()

This bug will appear when the following conditions are met:
        1. arg `nb_pkts` is greater than the `RTE_IXGBE_RXQ_REARM_THRESH`
        2. the application holds mbuf instead of releasing it immediately


On `_recv_raw_pkts_vec()`, if `nb_pkts` is greater than the
`RTE_IXGBE_RXQ_REARM_THRESH` and `rx_tail` wrap back to zero, 
in this case `rx_tail` may advance faster than `rxrearm_start`, which may cause
some unreleased mbufs be reused. 

e.g.

nb_rx_desc: 1024 RDH: 972 RDT: 991 rxrearm_nb: 991 rxrearm_start: 992 rx_tail:
959
nb_rx_desc: 1024 RDH: 1004 RDT: 1023 rxrearm_nb: 991 rxrearm_start: 0 rx_tail:
991
nb_rx_desc: 1024 RDH: 12 RDT: 31 rxrearm_nb: 991 rxrearm_start: 32 rx_tail:
1023
nb_rx_desc: 1024 RDH: 31 RDT: 63 rxrearm_nb: 960 rxrearm_start: 64 rx_tail: 0
nb_rx_desc: 1024 RDH: 95 RDT: 95 rxrearm_nb: 1016 rxrearm_start: 96 rx_tail: 88
nb_rx_desc: 1024 RDH: 95 RDT: 127 rxrearm_nb: 991 rxrearm_start: 128 rx_tail:
95
...
nb_rx_desc: 1024 RDH: 908 RDT: 927 rxrearm_nb: 991 rxrearm_start: 928 rx_tail:
895
nb_rx_desc: 1024 RDH: 940 RDT: 959 rxrearm_nb: 991 rxrearm_start: 960 rx_tail:
927
nb_rx_desc: 1024 RDH: 980 RDT: 991 rxrearm_nb: 991 rxrearm_start: 992 rx_tail:
959
nb_rx_desc: 1024 RDH: 991 RDT: 991 rxrearm_nb: 1026 rxrearm_start: 992 rx_tail:
994

when `rx_tail` catches up with `rxrearm_start`, 2(994 - 992) unreleased mbuf be
reused!

The simplest solution is to limit the size of `nb_pkts` to no more than
`RTE_IXGBE_RXQ_REARM_THRESH`. 
However, this method may affect the packet receiving speed of the application.

Just like it.

diff --git a/drivers/net/ixgbe/ixgbe_rxtx_vec_sse.c
b/drivers/net/ixgbe/ixgbe_rxtx_vec_sse.c
index 1eed949495..648ad9eadd 100644
--- a/drivers/net/ixgbe/ixgbe_rxtx_vec_sse.c
+++ b/drivers/net/ixgbe/ixgbe_rxtx_vec_sse.c
@@ -364,6 +364,12 @@ _recv_raw_pkts_vec(struct ixgbe_rx_queue *rxq, struct
rte_mbuf **rx_pkts,
        uint8_t vlan_flags;
        uint16_t udp_p_flag = 0; /* Rx Descriptor UDP header present */

+       /*
+        * If nb_pkts is greater than the threshold,
+        * it may cause some unreleased mbuf be reused.
+        */
+       nb_pkts = RTE_MIN(nb_pkts, RTE_IXGBE_RXQ_REARM_THRESH);
+
        /* nb_pkts has to be floor-aligned to RTE_IXGBE_DESCS_PER_LOOP */
        nb_pkts = RTE_ALIGN_FLOOR(nb_pkts, RTE_IXGBE_DESCS_PER_LOOP);


The attachment has a corresponding demo to reproduce this bug.

Thanks!

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