linux-kernel - Re: [PATCH net-next 6/6] net: hns3: use napi_consume

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Date:   Tue, 15 Sep 2020 15:04:13 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Saeed Mahameed <saeedm@...dia.com>,
        "tanhuazhong@...wei.com" <tanhuazhong@...wei.com>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     "yisen.zhuang@...wei.com" <yisen.zhuang@...wei.com>,
        "salil.mehta@...wei.com" <salil.mehta@...wei.com>,
        "linuxarm@...wei.com" <linuxarm@...wei.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kuba@...nel.org" <kuba@...nel.org>
Subject: Re: [PATCH net-next 6/6] net: hns3: use napi_consume_skb() when
 cleaning tx desc

On 2020/9/15 13:09, Saeed Mahameed wrote:
> On Mon, 2020-09-14 at 20:06 +0800, Huazhong Tan wrote:
>> From: Yunsheng Lin <linyunsheng@...wei.com>
>>
>> Use napi_consume_skb() to batch consuming skb when cleaning
>> tx desc in NAPI polling.
>>
>> Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
>> Signed-off-by: Huazhong Tan <tanhuazhong@...wei.com>
>> ---
>>  drivers/net/ethernet/hisilicon/hns3/hns3_enet.c    | 27 +++++++++++-
>> ----------
>>  drivers/net/ethernet/hisilicon/hns3/hns3_enet.h    |  2 +-
>>  drivers/net/ethernet/hisilicon/hns3/hns3_ethtool.c |  4 ++--
>>  3 files changed, 17 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
>> b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
>> index 4a49a76..feeaf75 100644
>> --- a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
>> +++ b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
>> @@ -2333,10 +2333,10 @@ static int hns3_alloc_buffer(struct
>> hns3_enet_ring *ring,
>>  }
>>  
>>  static void hns3_free_buffer(struct hns3_enet_ring *ring,
>> -			     struct hns3_desc_cb *cb)
>> +			     struct hns3_desc_cb *cb, int budget)
>>  {
>>  	if (cb->type == DESC_TYPE_SKB)
>> -		dev_kfree_skb_any((struct sk_buff *)cb->priv);
>> +		napi_consume_skb(cb->priv, budget);
> 
> This code can be reached from hns3_lb_clear_tx_ring() below which is
> your loopback test and called with non-zero budget, I am not sure you
> are allowed to call napi_consume_skb() with non-zero budget outside
> napi context, perhaps the cb->type for loopback test is different in lb
> test case ? Idk.. , please double check other code paths.

Yes, loopback test may call napi_consume_skb() with non-zero budget outside
napi context. Thanks for pointing out this case.

How about add the below WARN_ONCE() in napi_consume_skb() to catch this
kind of error?

WARN_ONCE(!in_serving_softirq(), "napi_consume_skb() is called with non-zero budget outside napi context");

> 
> [...]
> 
>>  static void hns3_lb_clear_tx_ring(struct hns3_nic_priv *priv, u32
>> start_ringid,
>> -				  u32 end_ringid, u32 budget)
>> +				  u32 end_ringid, int budget)
>>  {
>>  	u32 i;
>>  
>>  	for (i = start_ringid; i <= end_ringid; i++) {
>>  		struct hns3_enet_ring *ring = &priv->ring[i];
>>  
>> -		hns3_clean_tx_ring(ring);
>> +		hns3_clean_tx_ring(ring, budget);
>>  	}
>>  }
>>