netdev - Re: [PATCH bpf-next] bpf, sockmap: Manual deletion of sockmap elements in user mode is not allowed

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Date:   Tue, 15 Mar 2022 15:24:29 +0800
From:   wangyufen <wangyufen@...wei.com>
To:     Jakub Sitnicki <jakub@...udflare.com>
CC:     <ast@...nel.org>, <john.fastabend@...il.com>,
        <daniel@...earbox.net>, <lmb@...udflare.com>,
        <davem@...emloft.net>, <kafai@...com>, <dsahern@...nel.org>,
        <kuba@...nel.org>, <songliubraving@...com>, <yhs@...com>,
        <kpsingh@...nel.org>, <netdev@...r.kernel.org>,
        <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next] bpf, sockmap: Manual deletion of sockmap
 elements in user mode is not allowed


在 2022/3/14 23:30, Jakub Sitnicki 写道:
> On Mon, Mar 14, 2022 at 08:44 PM +08, Wang Yufen wrote:
>> A tcp socket in a sockmap. If user invokes bpf_map_delete_elem to delete
>> the sockmap element, the tcp socket will switch to use the TCP protocol
>> stack to send and receive packets. The switching process may cause some
>> issues, such as if some msgs exist in the ingress queue and are cleared
>> by sk_psock_drop(), the packets are lost, and the tcp data is abnormal.
>>
>> Signed-off-by: Wang Yufen <wangyufen@...wei.com>
>> ---
> Can you please tell us a bit more about the life-cycle of the socket in
> your workload? Questions that come to mind:
>
> 1) What triggers the removal of the socket from sockmap in your case?
We use sk_msg to redirect with sock hash, like this:

  skA   redirect    skB
  Tx <-----------> skB,Rx

And construct a scenario where the packet sending speed is high, the
packet receiving speed is slow, so the packets are stacked in the ingress
queue on the receiving side. In this case, if run bpf_map_delete_elem() to
delete the sockmap entry, will trigger the following procedure:

sock_hash_delete_elem()
   sock_map_unref()
     sk_psock_put()
       sk_psock_drop()
         sk_psock_stop()
           __sk_psock_zap_ingress()
             __sk_psock_purge_ingress_msg()

> 2) Would it still be a problem if removal from sockmap did not cause any
> packets to get dropped?
Yes, it still be a problem. If removal from sockmap  did not cause any
packets to get dropped, packet receiving process switches to use TCP
protocol stack. The packets in the psock ingress queue cannot be received

by the user.


Thanks.

>
> [...]
> .