netdev - Re: [PATCH net 2/7] virtio_net: Don't call free_old_xmit_skbs for xdp

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Date:   Fri, 18 Jan 2019 10:44:00 +0900
From:   Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To:     Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net 2/7] virtio_net: Don't call free_old_xmit_skbs for
 xdp_frames

On 2019/01/17 21:39, Jason Wang wrote:
> On 2019/1/17 下午7:20, Toshiaki Makita wrote:
>> When napi_tx is enabled, virtnet_poll_cleantx() called
>> free_old_xmit_skbs() even for xdp send queue.
>> This is bogus since the queue has xdp_frames, not sk_buffs, thus mangled
>> device tx bytes counters because skb->len is meaningless value, and even
>> triggered oops due to general protection fault on freeing them.
>>
>> Since xdp send queues do not aquire locks, old xdp_frames should be
>> freed only in virtnet_xdp_xmit(), so just skip free_old_xmit_skbs() for
>> xdp send queues.
>>
>> Similarly virtnet_poll_tx() called free_old_xmit_skbs(). This NAPI
>> handler is called even without calling start_xmit() because cb for tx is
>> by default enabled. Once the handler is called, it enabled the cb again,
>> and then the handler would be called again. We don't need this handler
>> for XDP, so don't enable cb as well as not calling free_old_xmit_skbs().
>>
>> Also, we need to disable tx NAPI when disabling XDP, so
>> virtnet_poll_tx() can safely access curr_queue_pairs and
>> xdp_queue_pairs, which are not atomically updated while disabling XDP.
> 
> 
> I suggest to split this into another patch or squash this part to patch 1.

This part is for invocation of is_xdp_raw_buffer_queue() from
virtnet_poll_tx(), which is added in this patch, so I'm thinking it's
more natural to keep this hunk in this patch.

-- 
Toshiaki Makita