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

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Date:   Tue, 29 Jun 2021 10:44:58 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Yonghong Song <yhs@...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 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.

Thanks for the review.