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Instead of > restarting the application to pick up the new tcp-cc, the next patch > will allow bpf iter with CAP_NET_ADMIN to do setsockopt(TCP_CONGESTION). > This requires locking the sock. > > Also, unlike the proc iteration (cat /proc/net/tcp[6]), the bpf iter > can inspect all fields of a tcp_sock. It will be useful to have a > consistent view on some of the fields (e.g. the ones reported in > tcp_get_info() that also acquires the sock lock). > > Double lock: locking the bucket first and then locking the sock could > lead to deadlock. This patch takes a batching approach similar to > inet_diag. While holding the bucket lock, it batch a number of sockets > into an array first and then unlock the bucket. Before doing show(), > it then calls lock_sock_fast(). > > In a machine with ~400k connections, the maximum number of > sk in a bucket of the established hashtable is 7. 0.02% of > the established connections fall into this bucket size. > > For listen hash (port+addr lhash2), the bucket is usually very > small also except for the SO_REUSEPORT use case which the > userspace could have one SO_REUSEPORT socket per thread. > > While batching is used, it can also minimize the chance of missing > sock in the setsockopt use case if the whole bucket is batched. > This patch will start with a batch array with INIT_BATCH_SZ (16) > which will be enough for the most common cases. bpf_iter_tcp_batch() > will try to realloc to a larger array to handle exception case (e.g. > the SO_REUSEPORT case in the lhash2). > > Signed-off-by: Martin KaFai Lau > --- > net/ipv4/tcp_ipv4.c | 236 ++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 230 insertions(+), 6 deletions(-) > > diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c > index 0d851289a89e..856144d33f52 100644 > --- a/net/ipv4/tcp_ipv4.c > +++ b/net/ipv4/tcp_ipv4.c > @@ -2687,6 +2687,15 @@ static int tcp4_seq_show(struct seq_file *seq, void *v) > } > > #ifdef CONFIG_BPF_SYSCALL > +struct bpf_tcp_iter_state { > + struct tcp_iter_state state; > + unsigned int cur_sk; > + unsigned int end_sk; > + unsigned int max_sk; > + struct sock **batch; > + bool st_bucket_done; > +}; > + > struct bpf_iter__tcp { > __bpf_md_ptr(struct bpf_iter_meta *, meta); > __bpf_md_ptr(struct sock_common *, sk_common); > @@ -2705,16 +2714,203 @@ static int tcp_prog_seq_show(struct bpf_prog *prog, struct bpf_iter_meta *meta, > return bpf_iter_run_prog(prog, &ctx); > } > > +static void bpf_iter_tcp_put_batch(struct bpf_tcp_iter_state *iter) > +{ > + while (iter->cur_sk < iter->end_sk) > + sock_put(iter->batch[iter->cur_sk++]); > +} > + > +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? > + 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? > + > if (sk->sk_state == TCP_TIME_WAIT) { > uid = 0; > } else if (sk->sk_state == TCP_NEW_SYN_RECV) { > @@ -2728,11 +2924,18 @@ static int bpf_iter_tcp_seq_show(struct seq_file *seq, void *v) > > meta.seq = seq; > prog = bpf_iter_get_info(&meta, false); > - return tcp_prog_seq_show(prog, &meta, v, uid); > + ret = tcp_prog_seq_show(prog, &meta, v, uid); > + > +unlock: > + if (sk_fullsock(sk)) > + unlock_sock_fast(sk, slow); > + return ret; > + > } > > static void bpf_iter_tcp_seq_stop(struct seq_file *seq, void *v) > { > + struct bpf_tcp_iter_state *iter = seq->private; > struct bpf_iter_meta meta; > struct bpf_prog *prog; > > @@ -2743,13 +2946,16 @@ static void bpf_iter_tcp_seq_stop(struct seq_file *seq, void *v) > (void)tcp_prog_seq_show(prog, &meta, v, 0); > } > > - tcp_seq_stop(seq, v); > + if (iter->cur_sk < iter->end_sk) { > + bpf_iter_tcp_put_batch(iter); > + iter->st_bucket_done = false; > + } > } > [...]