[Devel] [PATCH RH8 2/4] net/drivers/i40e: suppress warning on skb linearization

[Konstantin Khorenko]

On 06/18/2021 03:32 PM, Konstantin Khorenko wrote:
> On 06/18/2021 02:32 PM, Pavel Tikhomirov wrote:
>> From: Jan Dakinevich <jan.dakinevich at virtuozzo.com>
>>
>> Preallocate required memory with reasoned flags and skip memory
>> allocation step made by __pskb_pull_tail.
>>
>> https://pmc.acronis.com/browse/VSTOR-22811
>> Signed-off-by: Jan Dakinevich <jan.dakinevich at virtuozzo.com>
>> Acked-by: Konstantin Khorenko <khorenko at virtuozzo.com>
>>
>> khorenko@:
>> * skb buffer is provided to DMA zone, so allocation cannot be switched to
>>   kvmalloc(), so we just supress the warning here.
>>
>> * i40e_skb_linearize() code is taken from __pskb_pull_tail(),
>>   except for the size: we omit "+128" preallocation here
>>   because no future expansions are expected in this case.
>>
>> * there is another similar place: i40e_xmit_frame_ring() in i40evf/i40e_txrx.c,
>>   but as we did not trigger the warning there and as we just shut up the warning,
>>   we don't touch the second place in advance.
>>
>> https://jira.sw.ru/browse/PSBM-127846
>> (cherry-picked from vz7 commit 9b2d96420858 ("net/drivers/i40e: suppress
>> warning on skb linearization"))
>> Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
>> ---
>>  drivers/net/ethernet/intel/i40e/i40e_txrx.c | 19 ++++++++++++++++++-
>>  1 file changed, 18 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
>> index 1c56ec2421d4..edc094db762e 100644
>> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
>> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
>> @@ -3554,6 +3554,23 @@ static int i40e_xmit_xdp_ring(struct xdp_frame *xdpf,
>>  	return I40E_XDP_TX;
>>  }
>>
>> +
>> +static int i40e_skb_linearize(struct sk_buff *skb)
>> +{
>> +	int eat = (skb->tail + skb->data_len) - skb->end;
>> +
>> +	/* workaround to avoid allocation without __GFP_ORDER_NOWARN inside
>> +	 * __pskb_pull_tail()
>> +	 */
>> +	if (eat > 0 || skb_cloned(skb)) {
>> +		if (pskb_expand_head(skb, 0, eat > 0 ? eat : 0,
>> +				     GFP_ATOMIC | __GFP_ORDER_NOWARN))
>> +			return -ENOMEM;
>
> If we return not NULL here, then in case of out of memory we return NETDEV_TX_OK in i40e_xmit_frame_ring()
> which is a bit unexpected.
>

Please disregard my comment, the code is correct.

>
> void *__pskb_pull_tail(struct sk_buff *skb, int delta)
> {
>          /* If skb has not enough free space at tail, get new one
>           * plus 128 bytes for future expansions. If we have enough
>           * room at tail, reallocate without expansion only if skb is cloned.
>           */
>          int i, k, eat = (skb->tail + delta) - skb->end;
>
>          if (eat > 0 || skb_cloned(skb)) {
>                  if (pskb_expand_head(skb, 0, eat > 0 ? eat + 128 : 0,
>                                       GFP_ATOMIC))
>                          return NULL;
>          }
>
>
>
>
>> +	}
>> +
>> +	return __skb_linearize(skb);
>> +}
>> +
>>  /**
>>   * i40e_xmit_frame_ring - Sends buffer on Tx ring
>>   * @skb:     send buffer
>> @@ -3582,7 +3599,7 @@ static netdev_tx_t i40e_xmit_frame_ring(struct sk_buff *skb,
>>
>>  	count = i40e_xmit_descriptor_count(skb);
>>  	if (i40e_chk_linearize(skb, count)) {
>> -		if (__skb_linearize(skb)) {
>> +		if (i40e_skb_linearize(skb)) {
>>  			dev_kfree_skb_any(skb);
>>  			return NETDEV_TX_OK;
>>  		}
>>
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