From: zhoumin <zhoumin@loongson.cn>
To: "Zhang, Qi Z" <qi.z.zhang@intel.com>,
"Yang, Qiming" <qiming.yang@intel.com>,
"Wu, Wenjun1" <wenjun1.wu@intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
"maobibo@loongson.cn" <maobibo@loongson.cn>
Subject: Re: [PATCH v2] net/ixgbe: add proper memory barriers for some Rx functions
Date: Thu, 4 May 2023 20:42:50 +0800 [thread overview]
Message-ID: <88b24978-d541-b26f-1c3d-14b2c76a67f9@loongson.cn> (raw)
In-Reply-To: <DM4PR11MB5994C26B643A28A2CD4C3646D76B9@DM4PR11MB5994.namprd11.prod.outlook.com>
Hi Qi,
Thanks for your review.
On Fri, Apr 28, 2023 at 11:43AM, Zhang, Qi Z wrote:
>
>> -----Original Message-----
>> From: Min Zhou <zhoumin@loongson.cn>
>> Sent: Monday, April 24, 2023 5:06 PM
>> To: Yang, Qiming <qiming.yang@intel.com>; Wu, Wenjun1
>> <wenjun1.wu@intel.com>; zhoumin@loongson.cn
>> Cc: dev@dpdk.org; maobibo@loongson.cn
>> Subject: [PATCH v2] net/ixgbe: add proper memory barriers for some Rx
>> functions
>>
>> Segmentation fault has been observed while running the
>> ixgbe_recv_pkts_lro() function to receive packets on the Loongson 3C5000
>> processor which has 64 cores and 4 NUMA nodes.
>>
>> From the ixgbe_recv_pkts_lro() function, we found that as long as the first
>> packet has the EOP bit set, and the length of this packet is less than or equal
>> to rxq->crc_len, the segmentation fault will definitely happen even though
>> on the other platforms, such as X86.
>>
>> Because when processd the first packet the first_seg->next will be NULL, if at
>> the same time this packet has the EOP bit set and its length is less than or
>> equal to rxq->crc_len, the following loop will be excecuted:
>>
>> for (lp = first_seg; lp->next != rxm; lp = lp->next)
>> ;
>>
>> We know that the first_seg->next will be NULL under this condition. So the
>> expression of lp->next->next will cause the segmentation fault.
>>
>> Normally, the length of the first packet with EOP bit set will be greater than
>> rxq->crc_len. However, the out-of-order execution of CPU may make the
>> read ordering of the status and the rest of the descriptor fields in this
>> function not be correct. The related codes are as following:
>>
>> rxdp = &rx_ring[rx_id];
>> #1 staterr = rte_le_to_cpu_32(rxdp->wb.upper.status_error);
>>
>> if (!(staterr & IXGBE_RXDADV_STAT_DD))
>> break;
>>
>> #2 rxd = *rxdp;
>>
>> The sentence #2 may be executed before sentence #1. This action is likely to
>> make the ready packet zero length. If the packet is the first packet and has
>> the EOP bit set, the above segmentation fault will happen.
>>
>> So, we should add rte_rmb() to ensure the read ordering be correct. We also
>> did the same thing in the ixgbe_recv_pkts() function to make the rxd data be
>> valid even thougth we did not find segmentation fault in this function.
>>
>> Signed-off-by: Min Zhou <zhoumin@loongson.cn>
>> ---
>> v2:
>> - Make the calling of rte_rmb() for all platforms
>> ---
>> drivers/net/ixgbe/ixgbe_rxtx.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
>> index c9d6ca9efe..302a5ab7ff 100644
>> --- a/drivers/net/ixgbe/ixgbe_rxtx.c
>> +++ b/drivers/net/ixgbe/ixgbe_rxtx.c
>> @@ -1823,6 +1823,8 @@ ixgbe_recv_pkts(void *rx_queue, struct rte_mbuf
>> **rx_pkts,
>> staterr = rxdp->wb.upper.status_error;
>> if (!(staterr & rte_cpu_to_le_32(IXGBE_RXDADV_STAT_DD)))
>> break;
>> +
>> + rte_rmb();
> So "volatile" does not prevent re-order with Loongson compiler?
The memory consistency model of the LoongArch [1] uses the Weak
Consistency model in which memory operations can be reordered.
[1]
https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN#overview-of-memory-consistency
>> rxd = *rxdp;
>>
>> /*
>> @@ -2122,6 +2124,7 @@ ixgbe_recv_pkts_lro(void *rx_queue, struct
>> rte_mbuf **rx_pkts, uint16_t nb_pkts,
>> if (!(staterr & IXGBE_RXDADV_STAT_DD))
>> break;
>>
>> + rte_rmb();
>> rxd = *rxdp;
>>
>> PMD_RX_LOG(DEBUG, "port_id=%u queue_id=%u rx_id=%u "
>> --
>> 2.31.1
Best regards,
Min
next prev parent reply other threads:[~2023-05-04 12:42 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-24 9:05 Min Zhou
2023-04-28 3:43 ` Zhang, Qi Z
2023-04-28 6:27 ` Morten Brørup
2023-05-04 12:58 ` zhoumin
2023-05-04 12:42 ` zhoumin [this message]
2023-05-01 13:29 ` Konstantin Ananyev
2023-05-04 6:13 ` Ruifeng Wang
2023-05-05 1:45 ` zhoumin
2023-05-04 13:16 ` zhoumin
2023-05-04 13:21 ` Morten Brørup
2023-05-04 13:33 ` Zhang, Qi Z
2023-05-05 2:42 ` zhoumin
2023-05-06 1:30 ` Zhang, Qi Z
2023-05-05 1:54 ` zhoumin
2023-05-06 10:23 ` [PATCH v3] " Min Zhou
2023-05-08 6:03 ` Ruifeng Wang
2023-05-15 2:10 ` Zhang, Qi Z
2023-06-12 10:26 ` Thomas Monjalon
2023-06-12 11:58 ` zhoumin
2023-06-12 12:44 ` Thomas Monjalon
2023-06-13 1:42 ` zhoumin
2023-06-13 3:30 ` Jiawen Wu
2023-06-13 10:12 ` zhoumin
2023-06-14 10:58 ` Konstantin Ananyev
2023-06-13 9:25 ` Ruifeng Wang
2023-06-20 15:52 ` Thomas Monjalon
2023-06-21 6:50 ` Ruifeng Wang
2023-06-13 9:44 ` [PATCH v4] " Min Zhou
2023-06-13 10:20 ` Ruifeng Wang
2023-06-13 12:11 ` Zhang, Qi Z
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