netdev - Re: [PATCH bpf-next 6/8] bpf: tcp: bpf iter batching and lock

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Message-ID: <387750f4-4610-0c37-60c5-06e5a1c98e63@fb.com>
Date:   Tue, 29 Jun 2021 10:57:46 -0700
From:   Yonghong Song <yhs@...com>
To:     Martin KaFai Lau <kafai@...com>
CC:     <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <edumazet@...gle.com>, <kernel-team@...com>,
        Neal Cardwell <ncardwell@...gle.com>, <netdev@...r.kernel.org>,
        Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH bpf-next 6/8] bpf: tcp: bpf iter batching and lock_sock



On 6/29/21 10:44 AM, Martin KaFai Lau wrote:
> On Tue, Jun 29, 2021 at 10:27:17AM -0700, Yonghong Song wrote:
> [ ... ]
> 
>>> +static int bpf_iter_tcp_realloc_batch(struct bpf_tcp_iter_state *iter,
>>> +				      unsigned int new_batch_sz)
>>> +{
>>> +	struct sock **new_batch;
>>> +
>>> +	new_batch = kvmalloc(sizeof(*new_batch) * new_batch_sz, GFP_USER);
>>
>> Since we return -ENOMEM below, should we have __GFP_NOWARN in kvmalloc
>> flags?
> will add in v2.
> 
>>
>>> +	if (!new_batch)
>>> +		return -ENOMEM;
>>> +
>>> +	bpf_iter_tcp_put_batch(iter);
>>> +	kvfree(iter->batch);
>>> +	iter->batch = new_batch;
>>> +	iter->max_sk = new_batch_sz;
>>> +
>>> +	return 0;
>>> +}
>>> +
>> [...]
>>> +
>>>    static int bpf_iter_tcp_seq_show(struct seq_file *seq, void *v)
>>>    {
>>>    	struct bpf_iter_meta meta;
>>>    	struct bpf_prog *prog;
>>>    	struct sock *sk = v;
>>> +	bool slow;
>>>    	uid_t uid;
>>> +	int ret;
>>>    	if (v == SEQ_START_TOKEN)
>>>    		return 0;
>>> +	if (sk_fullsock(sk))
>>> +		slow = lock_sock_fast(sk);
>>> +
>>> +	if (unlikely(sk_unhashed(sk))) {
>>> +		ret = SEQ_SKIP;
>>> +		goto unlock;
>>> +	}
>>
>> I am not a tcp expert. Maybe a dummy question.
>> Is it possible to do setsockopt() for listening socket?
>> What will happen if the listening sock is unhashed after the
>> above check?
> It won't happen because the sk has been locked before doing the
> unhashed check.

Ya, that is true. I guess I probably mean TCP_TIME_WAIT and
TCP_NEW_SYN_RECV sockets. We cannot do setsockopt() for
TCP_TIME_WAIT sockets since user space shouldn't be able
to access the socket any more.

But how about TCP_NEW_SYN_RECV sockets?

> 
> Thanks for the review.
>