linux-kernel - Re: [PATCH net 3/3] hinic: fix bug of send pkts while setting channels

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Date:   Thu, 3 Sep 2020 22:18:51 +0800
From:   "luobin (L)" <luobin9@...wei.com>
To:     Eric Dumazet <eric.dumazet@...il.com>, <davem@...emloft.net>
CC:     <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <luoxianjun@...wei.com>, <yin.yinshi@...wei.com>,
        <cloud.wangxiaoyun@...wei.com>, <chiqijun@...wei.com>
Subject: Re: [PATCH net 3/3] hinic: fix bug of send pkts while setting
 channels

On 2020/9/2 18:16, Eric Dumazet wrote:
> 
> 
> On 9/2/20 2:41 AM, Luo bin wrote:
>> When calling hinic_close in hinic_set_channels, netif_carrier_off
>> and netif_tx_disable are excuted, and TX host resources are freed
>> after that. Core may call hinic_xmit_frame to send pkt after
>> netif_tx_disable within a short time, so we should judge whether
>> carrier is on before sending pkt otherwise the resources that
>> have already been freed in hinic_close may be accessed.
>>
>> Fixes: 2eed5a8b614b ("hinic: add set_channels ethtool_ops support")
>> Signed-off-by: Luo bin <luobin9@...wei.com>
>> ---
>>  drivers/net/ethernet/huawei/hinic/hinic_tx.c | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/drivers/net/ethernet/huawei/hinic/hinic_tx.c b/drivers/net/ethernet/huawei/hinic/hinic_tx.c
>> index a97498ee6914..a0662552a39c 100644
>> --- a/drivers/net/ethernet/huawei/hinic/hinic_tx.c
>> +++ b/drivers/net/ethernet/huawei/hinic/hinic_tx.c
>> @@ -531,6 +531,11 @@ netdev_tx_t hinic_xmit_frame(struct sk_buff *skb, struct net_device *netdev)
>>  	struct hinic_txq *txq;
>>  	struct hinic_qp *qp;
>>  
>> +	if (unlikely(!netif_carrier_ok(netdev))) {
>> +		dev_kfree_skb_any(skb);
>> +		return NETDEV_TX_OK;
>> +	}
>> +
>>  	txq = &nic_dev->txqs[q_id];
>>  	qp = container_of(txq->sq, struct hinic_qp, sq);
>>  
>>
> 
> Adding this kind of tests in fast path seems a big hammer to me.
> 
> See https://marc.info/?l=linux-netdev&m=159903844423389&w=2   for a similar problem.
> 
> Normally, after hinic_close() operation, no packet should be sent by core networking stack.
> 
> Trying to work around some core networking issue in each driver is a dead end.
Thanks for your review. I agree with what you said. Theoretically, core can't call ndo_start_xmit
to send packet after netif_tx_disable called by hinic_close because __QUEUE_STATE_DRV_XOFF bit is set
and this bit is protected by __netif_tx_lock but it does call hinic_xmit_frame after netif_tx_disable
in my debug message. I'll try to figure out why and fix it. It seems like that the patch from
https://marc.info/?l=linux-netdev&m=159903844423389&w=2 can't fix this problem.
> 
> 
> 
> 
> 
> 
> .
>