Merge branch 'bpf-tcp-exactly-once-socket-iteration'

Jordan Rife says:

====================
bpf: tcp: Exactly-once socket iteration

TCP socket iterators use iter->offset to track progress through a
bucket, which is a measure of the number of matching sockets from the
current bucket that have been seen or processed by the iterator. On
subsequent iterations, if the current bucket has unprocessed items, we
skip at least iter->offset matching items in the bucket before adding
any remaining items to the next batch. However, iter->offset isn't
always an accurate measure of "things already seen" when the underlying
bucket changes between reads, which can lead to repeated or skipped
sockets. Instead, this series remembers the cookies of the sockets we
haven't seen yet in the current bucket and resumes from the first cookie
in that list that we can find on the next iteration.

This is a continuation of the work started in [1]. This series largely
replicates the patterns applied to UDP socket iterators, applying them
instead to TCP socket iterators.

CHANGES
=======
v5 -> v6:
* In patch ten ("selftests/bpf: Create established sockets in socket
iterator tests"), use poll() to choose a socket that has a connection
ready to be accept()ed. Before, connect_to_server would set the
O_NONBLOCK flag on all listening sockets so that accept_from_one could
loop through them all and find the one that connect_to_addr_str
connected to. However, this is subtly buggy and could potentially lead
to test flakes, since the 3 way handshake isn't necessarily done when
connect returns, so it's possible none of the accept() calls succeed.
Use poll() instead to guarantee that the socket we accept() from is
ready and eliminate the need for the O_NONBLOCK flag (Martin).

v4 -> v5:
* Move WARN_ON_ONCE before the `done` label in patch two ("bpf: tcp:
Make sure iter->batch always contains a full bucket snapshot"")
(Martin).
* Remove unnecessary kfunc declaration in patch eleven ("selftests/bpf:
Create iter_tcp_destroy test program") (Martin).
* Make sure to close the socket fd at the end of `destroy` in patch
twelve ("selftests/bpf: Add tests for bucket resume logic in
established sockets") (Martin).

v3 -> v4:
* Drop braces around sk_nulls_for_each_from in patch five ("bpf: tcp:
Avoid socket skips and repeats during iteration") (Stanislav).
* Add a break after the TCP_SEQ_STATE_ESTABLISHED case in patch five
(Stanislav).
* Add an `if (sock_type == SOCK_STREAM)` check before assigning
TCP_LISTEN to skel->rodata->ss in patch eight ("selftests/bpf: Allow
for iteration over multiple states") to more clearly express the
intent that the option is only consumed for SOCK_STREAM tests
(Stanislav).
* Move the `i = 0` assignment into the for loop in patch ten
("selftests/bpf: Create established sockets in socket iterator
tests") (Stanislav).

v2 -> v3:
* Unroll the loop inside bpf_iter_tcp_batch to make the logic easier to
follow in patch two ("bpf: tcp: Make sure iter->batch always contains
a full bucket snapshot"). This gets rid of the `resizes` variable from
v2 and eliminates the extra conditional that checks how many batch
resize attempts have occurred so far (Stanislav).
Note: This changes the behavior slightly. Before, in the case that
the second call to tcp_seek_last_pos (and later bpf_iter_tcp_resume)
advances to a new bucket, which may happen if the current bucket is
emptied after releasing its lock, the `resizes` "budget" would be
reset, the net effect being that we would try a batch resize with
GFP_USER at most once per bucket. Now, we try to resize the batch
with GFP_USER at most once per call, so it makes it slightly more
likely that we hit the GFP_NOWAIT scenario. However, this edge case
should be rare in practice anyway, and the new behavior is more or
less consistent with the original retry logic, so avoid the loop and
prefer code clarity.
* Move the call to bpf_iter_tcp_put_batch out of
bpf_iter_tcp_realloc_batch and call it directly before invoking
bpf_iter_tcp_realloc_batch with GFP_USER inside bpf_iter_tcp_batch.
/Don't/ call it before invoking bpf_iter_tcp_realloc_batch the second
time while we hold the lock with GFP_NOWAIT. This avoids a conditional
inside bpf_iter_tcp_realloc_batch from v2 that only calls
bpf_iter_tcp_put_batch if flags != GFP_NOWAIT and is a bit more
explicit (Stanislav).
* Adjust patch five ("bpf: tcp: Avoid socket skips and repeats during
iteration") to fit with the new logic in patch two.

v1 -> v2:
* In patch five ("bpf: tcp: Avoid socket skips and repeats during
iteration"), remove unnecessary bucket bounds checks in
bpf_iter_tcp_resume. In either case, if st->bucket is outside the
current table's range then bpf_iter_tcp_resume_* calls *_get_first
which immediately returns NULL anyway and the logic will fall through.
(Martin)
* Add a check at the top of bpf_iter_tcp_resume_listening and
bpf_iter_tcp_resume_established to see if we're done with the current
bucket and advance it immediately instead of wasting time finding the
first matching socket in that bucket with
(listening|established)_get_first. In v1, we originally discussed
adding logic to advance the bucket in bpf_iter_tcp_seq_next and
bpf_iter_tcp_seq_stop, but after trying this the logic seemed harder
to track. Overall, keeping everything inside bpf_iter_tcp_resume_*
seemed a bit clearer. (Martin)
* Instead of using a timeout in the last patch ("selftests/bpf: Add
tests for bucket resume logic in established sockets") to wait for
sockets to leave the ehash table after calling close(), use
bpf_sock_destroy to deterministically destroy and remove them. This
introduces one more patch ("selftests/bpf: Create iter_tcp_destroy
test program") to create the iterator program that destroys a selected
socket. Drive this through a destroy() function in the last patch
which, just like close(), accepts a socket file descriptor. (Martin)
* Introduce one more patch ("selftests/bpf: Allow for iteration over
multiple states") to fix a latent bug in iter_tcp_soreuse where the
sk->sk_state != TCP_LISTEN check was ignored. Add the "ss" variable to
allow test code to configure which socket states to allow.

[1]: https://lore.kernel.org/bpf/[e-mail]/
====================

Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Martin KaFai Lau <[e-mail]>

net/ipv4/tcp_ipv4.c

···
 #include <linux/times.h>
 #include <linux/slab.h>
 #include <linux/sched.h>
+#include <linux/sock_diag.h>
 
 #include <net/net_namespace.h>
 #include <net/icmp.h>
···
 }
 
 #ifdef CONFIG_BPF_SYSCALL
+union bpf_tcp_iter_batch_item {
+	struct sock *sk;
+	__u64 cookie;
+};
+
 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;
+	union bpf_tcp_iter_batch_item *batch;
 };
 
 struct bpf_iter__tcp {
···
 
 static void bpf_iter_tcp_put_batch(struct bpf_tcp_iter_state *iter)
 {
-	while (iter->cur_sk < iter->end_sk)
-		sock_gen_put(iter->batch[iter->cur_sk++]);
+	union bpf_tcp_iter_batch_item *item;
+	unsigned int cur_sk = iter->cur_sk;
+	__u64 cookie;
+
+	/* Remember the cookies of the sockets we haven't seen yet, so we can
+	 * pick up where we left off next time around.
+	 */
+	while (cur_sk < iter->end_sk) {
+		item = &iter->batch[cur_sk++];
+		cookie = sock_gen_cookie(item->sk);
+		sock_gen_put(item->sk);
+		item->cookie = cookie;
+	}
 }
 
 static int bpf_iter_tcp_realloc_batch(struct bpf_tcp_iter_state *iter,
-				      unsigned int new_batch_sz)
+				      unsigned int new_batch_sz, gfp_t flags)
 {
-	struct sock **new_batch;
+	union bpf_tcp_iter_batch_item *new_batch;
 
 	new_batch = kvmalloc(sizeof(*new_batch) * new_batch_sz,
-			     GFP_USER | __GFP_NOWARN);
+			     flags | __GFP_NOWARN);
 	if (!new_batch)
 		return -ENOMEM;
 
-	bpf_iter_tcp_put_batch(iter);
+	memcpy(new_batch, iter->batch, sizeof(*iter->batch) * iter->end_sk);
 	kvfree(iter->batch);
 	iter->batch = new_batch;
 	iter->max_sk = new_batch_sz;
···
 	return 0;
 }
 
-static unsigned int bpf_iter_tcp_listening_batch(struct seq_file *seq,
-						 struct sock *start_sk)
+static struct sock *bpf_iter_tcp_resume_bucket(struct sock *first_sk,
+					       union bpf_tcp_iter_batch_item *cookies,
+					       int n_cookies)
+{
+	struct hlist_nulls_node *node;
+	struct sock *sk;
+	int i;
+
+	for (i = 0; i < n_cookies; i++) {
+		sk = first_sk;
+		sk_nulls_for_each_from(sk, node)
+			if (cookies[i].cookie == atomic64_read(&sk->sk_cookie))
+				return sk;
+	}
+
+	return NULL;
+}
+
+static struct sock *bpf_iter_tcp_resume_listening(struct seq_file *seq)
 {
 	struct inet_hashinfo *hinfo = seq_file_net(seq)->ipv4.tcp_death_row.hashinfo;
 	struct bpf_tcp_iter_state *iter = seq->private;
 	struct tcp_iter_state *st = &iter->state;
+	unsigned int find_cookie = iter->cur_sk;
+	unsigned int end_cookie = iter->end_sk;
+	int resume_bucket = st->bucket;
+	struct sock *sk;
+
+	if (end_cookie && find_cookie == end_cookie)
+		++st->bucket;
+
+	sk = listening_get_first(seq);
+	iter->cur_sk = 0;
+	iter->end_sk = 0;
+
+	if (sk && st->bucket == resume_bucket && end_cookie) {
+		sk = bpf_iter_tcp_resume_bucket(sk, &iter->batch[find_cookie],
+						end_cookie - find_cookie);
+		if (!sk) {
+			spin_unlock(&hinfo->lhash2[st->bucket].lock);
+			++st->bucket;
+			sk = listening_get_first(seq);
+		}
+	}
+
+	return sk;
+}
+
+static struct sock *bpf_iter_tcp_resume_established(struct seq_file *seq)
+{
+	struct inet_hashinfo *hinfo = seq_file_net(seq)->ipv4.tcp_death_row.hashinfo;
+	struct bpf_tcp_iter_state *iter = seq->private;
+	struct tcp_iter_state *st = &iter->state;
+	unsigned int find_cookie = iter->cur_sk;
+	unsigned int end_cookie = iter->end_sk;
+	int resume_bucket = st->bucket;
+	struct sock *sk;
+
+	if (end_cookie && find_cookie == end_cookie)
+		++st->bucket;
+
+	sk = established_get_first(seq);
+	iter->cur_sk = 0;
+	iter->end_sk = 0;
+
+	if (sk && st->bucket == resume_bucket && end_cookie) {
+		sk = bpf_iter_tcp_resume_bucket(sk, &iter->batch[find_cookie],
+						end_cookie - find_cookie);
+		if (!sk) {
+			spin_unlock_bh(inet_ehash_lockp(hinfo, st->bucket));
+			++st->bucket;
+			sk = established_get_first(seq);
+		}
+	}
+
+	return sk;
+}
+
+static struct sock *bpf_iter_tcp_resume(struct seq_file *seq)
+{
+	struct bpf_tcp_iter_state *iter = seq->private;
+	struct tcp_iter_state *st = &iter->state;
+	struct sock *sk = NULL;
+
+	switch (st->state) {
+	case TCP_SEQ_STATE_LISTENING:
+		sk = bpf_iter_tcp_resume_listening(seq);
+		if (sk)
+			break;
+		st->bucket = 0;
+		st->state = TCP_SEQ_STATE_ESTABLISHED;
+		fallthrough;
+	case TCP_SEQ_STATE_ESTABLISHED:
+		sk = bpf_iter_tcp_resume_established(seq);
+		break;
+	}
+
+	return sk;
+}
+
+static unsigned int bpf_iter_tcp_listening_batch(struct seq_file *seq,
+						 struct sock **start_sk)
+{
+	struct bpf_tcp_iter_state *iter = seq->private;
 	struct hlist_nulls_node *node;
 	unsigned int expected = 1;
 	struct sock *sk;
 
-	sock_hold(start_sk);
-	iter->batch[iter->end_sk++] = start_sk;
+	sock_hold(*start_sk);
+	iter->batch[iter->end_sk++].sk = *start_sk;
 
-	sk = sk_nulls_next(start_sk);
+	sk = sk_nulls_next(*start_sk);
+	*start_sk = NULL;
 	sk_nulls_for_each_from(sk, node) {
 		if (seq_sk_match(seq, sk)) {
 			if (iter->end_sk < iter->max_sk) {
 				sock_hold(sk);
-				iter->batch[iter->end_sk++] = sk;
+				iter->batch[iter->end_sk++].sk = sk;
+			} else if (!*start_sk) {
+				/* Remember where we left off. */
+				*start_sk = sk;
 			}
 			expected++;
 		}
 	}
-	spin_unlock(&hinfo->lhash2[st->bucket].lock);
 
 	return expected;
 }
 
 static unsigned int bpf_iter_tcp_established_batch(struct seq_file *seq,
-						   struct sock *start_sk)
+						   struct sock **start_sk)
 {
-	struct inet_hashinfo *hinfo = seq_file_net(seq)->ipv4.tcp_death_row.hashinfo;
 	struct bpf_tcp_iter_state *iter = seq->private;
-	struct tcp_iter_state *st = &iter->state;
 	struct hlist_nulls_node *node;
 	unsigned int expected = 1;
 	struct sock *sk;
 
-	sock_hold(start_sk);
-	iter->batch[iter->end_sk++] = start_sk;
+	sock_hold(*start_sk);
+	iter->batch[iter->end_sk++].sk = *start_sk;
 
-	sk = sk_nulls_next(start_sk);
+	sk = sk_nulls_next(*start_sk);
+	*start_sk = NULL;
 	sk_nulls_for_each_from(sk, node) {
 		if (seq_sk_match(seq, sk)) {
 			if (iter->end_sk < iter->max_sk) {
 				sock_hold(sk);
-				iter->batch[iter->end_sk++] = sk;
+				iter->batch[iter->end_sk++].sk = sk;
+			} else if (!*start_sk) {
+				/* Remember where we left off. */
+				*start_sk = sk;
 			}
 			expected++;
 		}
 	}
-	spin_unlock_bh(inet_ehash_lockp(hinfo, st->bucket));
 
 	return expected;
 }
 
-static struct sock *bpf_iter_tcp_batch(struct seq_file *seq)
+static unsigned int bpf_iter_fill_batch(struct seq_file *seq,
+					struct sock **start_sk)
+{
+	struct bpf_tcp_iter_state *iter = seq->private;
+	struct tcp_iter_state *st = &iter->state;
+
+	if (st->state == TCP_SEQ_STATE_LISTENING)
+		return bpf_iter_tcp_listening_batch(seq, start_sk);
+	else
+		return bpf_iter_tcp_established_batch(seq, start_sk);
+}
+
+static void bpf_iter_tcp_unlock_bucket(struct seq_file *seq)
 {
 	struct inet_hashinfo *hinfo = seq_file_net(seq)->ipv4.tcp_death_row.hashinfo;
 	struct bpf_tcp_iter_state *iter = seq->private;
 	struct tcp_iter_state *st = &iter->state;
+
+	if (st->state == TCP_SEQ_STATE_LISTENING)
+		spin_unlock(&hinfo->lhash2[st->bucket].lock);
+	else
+		spin_unlock_bh(inet_ehash_lockp(hinfo, st->bucket));
+}
+
+static struct sock *bpf_iter_tcp_batch(struct seq_file *seq)
+{
+	struct bpf_tcp_iter_state *iter = seq->private;
 	unsigned int expected;
-	bool resized = false;
 	struct sock *sk;
+	int err;
 
-	/* The st->bucket is done.  Directly advance to the next
-	 * bucket instead of having the tcp_seek_last_pos() to skip
-	 * one by one in the current bucket and eventually find out
-	 * it has to advance to the next bucket.
-	 */
-	if (iter->st_bucket_done) {
-		st->offset = 0;
-		st->bucket++;
-		if (st->state == TCP_SEQ_STATE_LISTENING &&
-		    st->bucket > hinfo->lhash2_mask) {
-			st->state = TCP_SEQ_STATE_ESTABLISHED;
-			st->bucket = 0;
-		}
-	}
-
-again:
-	/* Get a new batch */
-	iter->cur_sk = 0;
-	iter->end_sk = 0;
-	iter->st_bucket_done = false;
-
-	sk = tcp_seek_last_pos(seq);
+	sk = bpf_iter_tcp_resume(seq);
 	if (!sk)
 		return NULL; /* Done */
 
-	if (st->state == TCP_SEQ_STATE_LISTENING)
-		expected = bpf_iter_tcp_listening_batch(seq, sk);
-	else
-		expected = bpf_iter_tcp_established_batch(seq, sk);
+	expected = bpf_iter_fill_batch(seq, &sk);
+	if (likely(iter->end_sk == expected))
+		goto done;
 
-	if (iter->end_sk == expected) {
-		iter->st_bucket_done = true;
-		return sk;
+	/* Batch size was too small. */
+	bpf_iter_tcp_unlock_bucket(seq);
+	bpf_iter_tcp_put_batch(iter);
+	err = bpf_iter_tcp_realloc_batch(iter, expected * 3 / 2,
+					 GFP_USER);
+	if (err)
+		return ERR_PTR(err);
+
+	sk = bpf_iter_tcp_resume(seq);
+	if (!sk)
+		return NULL; /* Done */
+
+	expected = bpf_iter_fill_batch(seq, &sk);
+	if (likely(iter->end_sk == expected))
+		goto done;
+
+	/* Batch size was still too small. Hold onto the lock while we try
+	 * again with a larger batch to make sure the current bucket's size
+	 * does not change in the meantime.
+	 */
+	err = bpf_iter_tcp_realloc_batch(iter, expected, GFP_NOWAIT);
+	if (err) {
+		bpf_iter_tcp_unlock_bucket(seq);
+		return ERR_PTR(err);
 	}
 
-	if (!resized && !bpf_iter_tcp_realloc_batch(iter, expected * 3 / 2)) {
-		resized = true;
-		goto again;
-	}
-
-	return sk;
+	expected = bpf_iter_fill_batch(seq, &sk);
+	WARN_ON_ONCE(iter->end_sk != expected);
+done:
+	bpf_iter_tcp_unlock_bucket(seq);
+	return iter->batch[0].sk;
 }
 
 static void *bpf_iter_tcp_seq_start(struct seq_file *seq, loff_t *pos)
···
 		 * meta.seq_num is used instead.
 		 */
 		st->num++;
-		/* Move st->offset to the next sk in the bucket such that
-		 * the future start() will resume at st->offset in
-		 * st->bucket.  See tcp_seek_last_pos().
-		 */
-		st->offset++;
-		sock_gen_put(iter->batch[iter->cur_sk++]);
+		sock_gen_put(iter->batch[iter->cur_sk++].sk);
 	}
 
 	if (iter->cur_sk < iter->end_sk)
-		sk = iter->batch[iter->cur_sk];
+		sk = iter->batch[iter->cur_sk].sk;
 	else
 		sk = bpf_iter_tcp_batch(seq);
 
···
 			(void)tcp_prog_seq_show(prog, &meta, v, 0);
 	}
 
-	if (iter->cur_sk < iter->end_sk) {
+	if (iter->cur_sk < iter->end_sk)
 		bpf_iter_tcp_put_batch(iter);
-		iter->st_bucket_done = false;
-	}
 }
 
 static const struct seq_operations bpf_iter_tcp_seq_ops = {
···
 	if (err)
 		return err;
 
-	err = bpf_iter_tcp_realloc_batch(iter, INIT_BATCH_SZ);
+	err = bpf_iter_tcp_realloc_batch(iter, INIT_BATCH_SZ, GFP_USER);
 	if (err) {
 		bpf_iter_fini_seq_net(priv_data);
 		return err;

tools/testing/selftests/bpf/prog_tests/sock_iter_batch.c

···
 // SPDX-License-Identifier: GPL-2.0
 // Copyright (c) 2024 Meta
 
+#include <poll.h>
 #include <test_progs.h>
 #include "network_helpers.h"
 #include "sock_iter_batch.skel.h"
 
 #define TEST_NS "sock_iter_batch_netns"
+#define TEST_CHILD_NS "sock_iter_batch_child_netns"
 
 static const int init_batch_size = 16;
 static const int nr_soreuse = 4;
···
 	return nth_sock_idx;
 }
 
+static void destroy(int fd)
+{
+	struct sock_iter_batch *skel = NULL;
+	__u64 cookie = socket_cookie(fd);
+	struct bpf_link *link = NULL;
+	int iter_fd = -1;
+	int nread;
+	__u64 out;
+
+	skel = sock_iter_batch__open();
+	if (!ASSERT_OK_PTR(skel, "sock_iter_batch__open"))
+		goto done;
+
+	skel->rodata->destroy_cookie = cookie;
+
+	if (!ASSERT_OK(sock_iter_batch__load(skel), "sock_iter_batch__load"))
+		goto done;
+
+	link = bpf_program__attach_iter(skel->progs.iter_tcp_destroy, NULL);
+	if (!ASSERT_OK_PTR(link, "bpf_program__attach_iter"))
+		goto done;
+
+	iter_fd = bpf_iter_create(bpf_link__fd(link));
+	if (!ASSERT_OK_FD(iter_fd, "bpf_iter_create"))
+		goto done;
+
+	/* Delete matching socket. */
+	nread = read(iter_fd, &out, sizeof(out));
+	ASSERT_GE(nread, 0, "nread");
+	if (nread)
+		ASSERT_EQ(out, cookie, "cookie matches");
+done:
+	if (iter_fd >= 0)
+		close(iter_fd);
+	bpf_link__destroy(link);
+	sock_iter_batch__destroy(skel);
+	close(fd);
+}
+
 static int get_seen_count(int fd, struct sock_count counts[], int n)
 {
 	__u64 cookie = socket_cookie(fd);
···
 	ASSERT_EQ(seen_once, n, "seen_once");
 }
 
+static int accept_from_one(struct pollfd *server_poll_fds,
+			   int server_poll_fds_len)
+{
+	static const int poll_timeout_ms = 5000; /* 5s */
+	int ret;
+	int i;
+
+	ret = poll(server_poll_fds, server_poll_fds_len, poll_timeout_ms);
+	if (!ASSERT_EQ(ret, 1, "poll"))
+		return -1;
+
+	for (i = 0; i < server_poll_fds_len; i++)
+		if (server_poll_fds[i].revents & POLLIN)
+			return accept(server_poll_fds[i].fd, NULL, NULL);
+
+	return -1;
+}
+
+static int *connect_to_server(int family, int sock_type, const char *addr,
+			      __u16 port, int nr_connects, int *server_fds,
+			      int server_fds_len)
+{
+	struct pollfd *server_poll_fds = NULL;
+	int *established_socks = NULL;
+	int i;
+
+	server_poll_fds = calloc(server_fds_len, sizeof(*server_poll_fds));
+	if (!ASSERT_OK_PTR(server_poll_fds, "server_poll_fds"))
+		return NULL;
+
+	for (i = 0; i < server_fds_len; i++) {
+		server_poll_fds[i].fd = server_fds[i];
+		server_poll_fds[i].events = POLLIN;
+	}
+
+	i = 0;
+
+	established_socks = malloc(sizeof(*established_socks) * nr_connects*2);
+	if (!ASSERT_OK_PTR(established_socks, "established_socks"))
+		goto error;
+
+	while (nr_connects--) {
+		established_socks[i] = connect_to_addr_str(family, sock_type,
+							   addr, port, NULL);
+		if (!ASSERT_OK_FD(established_socks[i], "connect_to_addr_str"))
+			goto error;
+		i++;
+		established_socks[i] = accept_from_one(server_poll_fds,
+						       server_fds_len);
+		if (!ASSERT_OK_FD(established_socks[i], "accept_from_one"))
+			goto error;
+		i++;
+	}
+
+	free(server_poll_fds);
+	return established_socks;
+error:
+	free_fds(established_socks, i);
+	free(server_poll_fds);
+	return NULL;
+}
+
 static void remove_seen(int family, int sock_type, const char *addr, __u16 port,
-			int *socks, int socks_len, struct sock_count *counts,
+			int *socks, int socks_len, int *established_socks,
+			int established_socks_len, struct sock_count *counts,
 			int counts_len, struct bpf_link *link, int iter_fd)
 {
 	int close_idx;
···
 			       counts_len);
 }
 
+static void remove_seen_established(int family, int sock_type, const char *addr,
+				    __u16 port, int *listen_socks,
+				    int listen_socks_len, int *established_socks,
+				    int established_socks_len,
+				    struct sock_count *counts, int counts_len,
+				    struct bpf_link *link, int iter_fd)
+{
+	int close_idx;
+
+	/* Iterate through all listening sockets. */
+	read_n(iter_fd, listen_socks_len, counts, counts_len);
+
+	/* Make sure we saw all listening sockets exactly once. */
+	check_n_were_seen_once(listen_socks, listen_socks_len, listen_socks_len,
+			       counts, counts_len);
+
+	/* Leave one established socket. */
+	read_n(iter_fd, established_socks_len - 1, counts, counts_len);
+
+	/* Close a socket we've already seen to remove it from the bucket. */
+	close_idx = get_nth_socket(established_socks, established_socks_len,
+				   link, listen_socks_len + 1);
+	if (!ASSERT_GE(close_idx, 0, "close_idx"))
+		return;
+	destroy(established_socks[close_idx]);
+	established_socks[close_idx] = -1;
+
+	/* Iterate through the rest of the sockets. */
+	read_n(iter_fd, -1, counts, counts_len);
+
+	/* Make sure the last socket wasn't skipped and that there were no
+	 * repeats.
+	 */
+	check_n_were_seen_once(established_socks, established_socks_len,
+			       established_socks_len - 1, counts, counts_len);
+}
+
 static void remove_unseen(int family, int sock_type, const char *addr,
 			  __u16 port, int *socks, int socks_len,
+			  int *established_socks, int established_socks_len,
 			  struct sock_count *counts, int counts_len,
 			  struct bpf_link *link, int iter_fd)
 {
···
 			       counts_len);
 }
 
+static void remove_unseen_established(int family, int sock_type,
+				      const char *addr, __u16 port,
+				      int *listen_socks, int listen_socks_len,
+				      int *established_socks,
+				      int established_socks_len,
+				      struct sock_count *counts, int counts_len,
+				      struct bpf_link *link, int iter_fd)
+{
+	int close_idx;
+
+	/* Iterate through all listening sockets. */
+	read_n(iter_fd, listen_socks_len, counts, counts_len);
+
+	/* Make sure we saw all listening sockets exactly once. */
+	check_n_were_seen_once(listen_socks, listen_socks_len, listen_socks_len,
+			       counts, counts_len);
+
+	/* Iterate through the first established socket. */
+	read_n(iter_fd, 1, counts, counts_len);
+
+	/* Make sure we saw one established socks. */
+	check_n_were_seen_once(established_socks, established_socks_len, 1,
+			       counts, counts_len);
+
+	/* Close what would be the next socket in the bucket to exercise the
+	 * condition where we need to skip past the first cookie we remembered.
+	 */
+	close_idx = get_nth_socket(established_socks, established_socks_len,
+				   link, listen_socks_len + 1);
+	if (!ASSERT_GE(close_idx, 0, "close_idx"))
+		return;
+
+	destroy(established_socks[close_idx]);
+	established_socks[close_idx] = -1;
+
+	/* Iterate through the rest of the sockets. */
+	read_n(iter_fd, -1, counts, counts_len);
+
+	/* Make sure the remaining sockets were seen exactly once and that we
+	 * didn't repeat the socket that was already seen.
+	 */
+	check_n_were_seen_once(established_socks, established_socks_len,
+			       established_socks_len - 1, counts, counts_len);
+}
+
 static void remove_all(int family, int sock_type, const char *addr,
 		       __u16 port, int *socks, int socks_len,
+		       int *established_socks, int established_socks_len,
 		       struct sock_count *counts, int counts_len,
 		       struct bpf_link *link, int iter_fd)
 {
···
 	ASSERT_EQ(read_n(iter_fd, -1, counts, counts_len), 0, "read_n");
 }
 
+static void remove_all_established(int family, int sock_type, const char *addr,
+				   __u16 port, int *listen_socks,
+				   int listen_socks_len, int *established_socks,
+				   int established_socks_len,
+				   struct sock_count *counts, int counts_len,
+				   struct bpf_link *link, int iter_fd)
+{
+	int *close_idx = NULL;
+	int i;
+
+	/* Iterate through all listening sockets. */
+	read_n(iter_fd, listen_socks_len, counts, counts_len);
+
+	/* Make sure we saw all listening sockets exactly once. */
+	check_n_were_seen_once(listen_socks, listen_socks_len, listen_socks_len,
+			       counts, counts_len);
+
+	/* Iterate through the first established socket. */
+	read_n(iter_fd, 1, counts, counts_len);
+
+	/* Make sure we saw one established socks. */
+	check_n_were_seen_once(established_socks, established_socks_len, 1,
+			       counts, counts_len);
+
+	/* Close all remaining sockets to exhaust the list of saved cookies and
+	 * exit without putting any sockets into the batch on the next read.
+	 */
+	close_idx = malloc(sizeof(int) * (established_socks_len - 1));
+	if (!ASSERT_OK_PTR(close_idx, "close_idx malloc"))
+		return;
+	for (i = 0; i < established_socks_len - 1; i++) {
+		close_idx[i] = get_nth_socket(established_socks,
+					      established_socks_len, link,
+					      listen_socks_len + i);
+		if (!ASSERT_GE(close_idx[i], 0, "close_idx"))
+			return;
+	}
+
+	for (i = 0; i < established_socks_len - 1; i++) {
+		destroy(established_socks[close_idx[i]]);
+		established_socks[close_idx[i]] = -1;
+	}
+
+	/* Make sure there are no more sockets returned */
+	ASSERT_EQ(read_n(iter_fd, -1, counts, counts_len), 0, "read_n");
+	free(close_idx);
+}
+
 static void add_some(int family, int sock_type, const char *addr, __u16 port,
-		     int *socks, int socks_len, struct sock_count *counts,
+		     int *socks, int socks_len, int *established_socks,
+		     int established_socks_len, struct sock_count *counts,
 		     int counts_len, struct bpf_link *link, int iter_fd)
 {
 	int *new_socks = NULL;
···
 	free_fds(new_socks, socks_len);
 }
 
+static void add_some_established(int family, int sock_type, const char *addr,
+				 __u16 port, int *listen_socks,
+				 int listen_socks_len, int *established_socks,
+				 int established_socks_len,
+				 struct sock_count *counts,
+				 int counts_len, struct bpf_link *link,
+				 int iter_fd)
+{
+	int *new_socks = NULL;
+
+	/* Iterate through all listening sockets. */
+	read_n(iter_fd, listen_socks_len, counts, counts_len);
+
+	/* Make sure we saw all listening sockets exactly once. */
+	check_n_were_seen_once(listen_socks, listen_socks_len, listen_socks_len,
+			       counts, counts_len);
+
+	/* Iterate through the first established_socks_len - 1 sockets. */
+	read_n(iter_fd, established_socks_len - 1, counts, counts_len);
+
+	/* Make sure we saw established_socks_len - 1 sockets exactly once. */
+	check_n_were_seen_once(established_socks, established_socks_len,
+			       established_socks_len - 1, counts, counts_len);
+
+	/* Double the number of established sockets in the bucket. */
+	new_socks = connect_to_server(family, sock_type, addr, port,
+				      established_socks_len / 2, listen_socks,
+				      listen_socks_len);
+	if (!ASSERT_OK_PTR(new_socks, "connect_to_server"))
+		goto done;
+
+	/* Iterate through the rest of the sockets. */
+	read_n(iter_fd, -1, counts, counts_len);
+
+	/* Make sure each of the original sockets was seen exactly once. */
+	check_n_were_seen_once(listen_socks, listen_socks_len, listen_socks_len,
+			       counts, counts_len);
+	check_n_were_seen_once(established_socks, established_socks_len,
+			       established_socks_len, counts, counts_len);
+done:
+	free_fds(new_socks, established_socks_len);
+}
+
 static void force_realloc(int family, int sock_type, const char *addr,
 			  __u16 port, int *socks, int socks_len,
+			  int *established_socks, int established_socks_len,
 			  struct sock_count *counts, int counts_len,
 			  struct bpf_link *link, int iter_fd)
 {
···
 	free_fds(new_socks, socks_len);
 }
 
+static void force_realloc_established(int family, int sock_type,
+				      const char *addr, __u16 port,
+				      int *listen_socks, int listen_socks_len,
+				      int *established_socks,
+				      int established_socks_len,
+				      struct sock_count *counts, int counts_len,
+				      struct bpf_link *link, int iter_fd)
+{
+	/* Iterate through all sockets to trigger a realloc. */
+	read_n(iter_fd, -1, counts, counts_len);
+
+	/* Make sure each socket was seen exactly once. */
+	check_n_were_seen_once(listen_socks, listen_socks_len, listen_socks_len,
+			       counts, counts_len);
+	check_n_were_seen_once(established_socks, established_socks_len,
+			       established_socks_len, counts, counts_len);
+}
+
 struct test_case {
 	void (*test)(int family, int sock_type, const char *addr, __u16 port,
-		     int *socks, int socks_len, struct sock_count *counts,
+		     int *socks, int socks_len, int *established_socks,
+		     int established_socks_len, struct sock_count *counts,
 		     int counts_len, struct bpf_link *link, int iter_fd);
 	const char *description;
+	int ehash_buckets;
+	int connections;
 	int init_socks;
 	int max_socks;
 	int sock_type;
···
 		.family = AF_INET6,
 		.test = force_realloc,
 	},
+	{
+		.description = "tcp: resume after removing a seen socket (listening)",
+		.init_socks = nr_soreuse,
+		.max_socks = nr_soreuse,
+		.sock_type = SOCK_STREAM,
+		.family = AF_INET6,
+		.test = remove_seen,
+	},
+	{
+		.description = "tcp: resume after removing one unseen socket (listening)",
+		.init_socks = nr_soreuse,
+		.max_socks = nr_soreuse,
+		.sock_type = SOCK_STREAM,
+		.family = AF_INET6,
+		.test = remove_unseen,
+	},
+	{
+		.description = "tcp: resume after removing all unseen sockets (listening)",
+		.init_socks = nr_soreuse,
+		.max_socks = nr_soreuse,
+		.sock_type = SOCK_STREAM,
+		.family = AF_INET6,
+		.test = remove_all,
+	},
+	{
+		.description = "tcp: resume after adding a few sockets (listening)",
+		.init_socks = nr_soreuse,
+		.max_socks = nr_soreuse,
+		.sock_type = SOCK_STREAM,
+		/* Use AF_INET so that new sockets are added to the head of the
+		 * bucket's list.
+		 */
+		.family = AF_INET,
+		.test = add_some,
+	},
+	{
+		.description = "tcp: force a realloc to occur (listening)",
+		.init_socks = init_batch_size,
+		.max_socks = init_batch_size * 2,
+		.sock_type = SOCK_STREAM,
+		/* Use AF_INET6 so that new sockets are added to the tail of the
+		 * bucket's list, needing to be added to the next batch to force
+		 * a realloc.
+		 */
+		.family = AF_INET6,
+		.test = force_realloc,
+	},
+	{
+		.description = "tcp: resume after removing a seen socket (established)",
+		/* Force all established sockets into one bucket */
+		.ehash_buckets = 1,
+		.connections = nr_soreuse,
+		.init_socks = nr_soreuse,
+		/* Room for connect()ed and accept()ed sockets */
+		.max_socks = nr_soreuse * 3,
+		.sock_type = SOCK_STREAM,
+		.family = AF_INET6,
+		.test = remove_seen_established,
+	},
+	{
+		.description = "tcp: resume after removing one unseen socket (established)",
+		/* Force all established sockets into one bucket */
+		.ehash_buckets = 1,
+		.connections = nr_soreuse,
+		.init_socks = nr_soreuse,
+		/* Room for connect()ed and accept()ed sockets */
+		.max_socks = nr_soreuse * 3,
+		.sock_type = SOCK_STREAM,
+		.family = AF_INET6,
+		.test = remove_unseen_established,
+	},
+	{
+		.description = "tcp: resume after removing all unseen sockets (established)",
+		/* Force all established sockets into one bucket */
+		.ehash_buckets = 1,
+		.connections = nr_soreuse,
+		.init_socks = nr_soreuse,
+		/* Room for connect()ed and accept()ed sockets */
+		.max_socks = nr_soreuse * 3,
+		.sock_type = SOCK_STREAM,
+		.family = AF_INET6,
+		.test = remove_all_established,
+	},
+	{
+		.description = "tcp: resume after adding a few sockets (established)",
+		/* Force all established sockets into one bucket */
+		.ehash_buckets = 1,
+		.connections = nr_soreuse,
+		.init_socks = nr_soreuse,
+		/* Room for connect()ed and accept()ed sockets */
+		.max_socks = nr_soreuse * 3,
+		.sock_type = SOCK_STREAM,
+		.family = AF_INET6,
+		.test = add_some_established,
+	},
+	{
+		.description = "tcp: force a realloc to occur (established)",
+		/* Force all established sockets into one bucket */
+		.ehash_buckets = 1,
+		/* Bucket size will need to double when going from listening to
+		 * established sockets.
+		 */
+		.connections = init_batch_size,
+		.init_socks = nr_soreuse,
+		/* Room for connect()ed and accept()ed sockets */
+		.max_socks = nr_soreuse + (init_batch_size * 2),
+		.sock_type = SOCK_STREAM,
+		.family = AF_INET6,
+		.test = force_realloc_established,
+	},
 };
 
 static void do_resume_test(struct test_case *tc)
 {
 	struct sock_iter_batch *skel = NULL;
+	struct sock_count *counts = NULL;
 	static const __u16 port = 10001;
+	struct nstoken *nstoken = NULL;
 	struct bpf_link *link = NULL;
-	struct sock_count *counts;
+	int *established_fds = NULL;
 	int err, iter_fd = -1;
 	const char *addr;
 	int *fds = NULL;
-	int local_port;
+
+	if (tc->ehash_buckets) {
+		SYS_NOFAIL("ip netns del " TEST_CHILD_NS);
+		SYS(done, "sysctl -wq net.ipv4.tcp_child_ehash_entries=%d",
+		    tc->ehash_buckets);
+		SYS(done, "ip netns add %s", TEST_CHILD_NS);
+		SYS(done, "ip -net %s link set dev lo up", TEST_CHILD_NS);
+		nstoken = open_netns(TEST_CHILD_NS);
+		if (!ASSERT_OK_PTR(nstoken, "open_child_netns"))
+			goto done;
+	}
 
 	counts = calloc(tc->max_socks, sizeof(*counts));
 	if (!ASSERT_OK_PTR(counts, "counts"))
···
 				     tc->init_socks);
 	if (!ASSERT_OK_PTR(fds, "start_reuseport_server"))
 		goto done;
-	local_port = get_socket_local_port(*fds);
-	if (!ASSERT_GE(local_port, 0, "get_socket_local_port"))
-		goto done;
-	skel->rodata->ports[0] = ntohs(local_port);
+	if (tc->connections) {
+		established_fds = connect_to_server(tc->family, tc->sock_type,
+						    addr, port,
+						    tc->connections, fds,
+						    tc->init_socks);
+		if (!ASSERT_OK_PTR(established_fds, "connect_to_server"))
+			goto done;
+	}
+	skel->rodata->ports[0] = 0;
+	skel->rodata->ports[1] = 0;
 	skel->rodata->sf = tc->family;
+	skel->rodata->ss = 0;
 
 	err = sock_iter_batch__load(skel);
 	if (!ASSERT_OK(err, "sock_iter_batch__load"))
···
 		goto done;
 
 	tc->test(tc->family, tc->sock_type, addr, port, fds, tc->init_socks,
-		 counts, tc->max_socks, link, iter_fd);
+		 established_fds, tc->connections*2, counts, tc->max_socks,
+		 link, iter_fd);
 done:
+	close_netns(nstoken);
+	SYS_NOFAIL("ip netns del " TEST_CHILD_NS);
+	SYS_NOFAIL("sysctl -w net.ipv4.tcp_child_ehash_entries=0");
 	free(counts);
 	free_fds(fds, tc->init_socks);
+	free_fds(established_fds, tc->connections*2);
 	if (iter_fd >= 0)
 		close(iter_fd);
 	bpf_link__destroy(link);
···
 		skel->rodata->ports[i] = ntohs(local_port);
 	}
 	skel->rodata->sf = AF_INET6;
+	if (sock_type == SOCK_STREAM)
+		skel->rodata->ss = TCP_LISTEN;
 
 	err = sock_iter_batch__load(skel);
 	if (!ASSERT_OK(err, "sock_iter_batch__load"))

tools/testing/selftests/bpf/progs/sock_iter_batch.c

···
 }
 
 volatile const unsigned int sf;
+volatile const unsigned int ss;
 volatile const __u16 ports[2];
 unsigned int bucket[2];
 
···
 	sock_cookie = bpf_get_socket_cookie(sk);
 	sk = bpf_core_cast(sk, struct sock);
 	if (sk->sk_family != sf ||
-	    sk->sk_state != TCP_LISTEN ||
-	    sk->sk_family == AF_INET6 ?
+	    (ss && sk->sk_state != ss) ||
+	    (sk->sk_family == AF_INET6 ?
 	    !ipv6_addr_loopback(&sk->sk_v6_rcv_saddr) :
-	    !ipv4_addr_loopback(sk->sk_rcv_saddr))
+	    !ipv4_addr_loopback(sk->sk_rcv_saddr)))
 		return 0;
 
 	if (sk->sk_num == ports[0])
 		idx = 0;
 	else if (sk->sk_num == ports[1])
 		idx = 1;
+	else if (!ports[0] && !ports[1])
+		idx = 0;
 	else
 		return 0;
 
···
 	hinfo = net->ipv4.tcp_death_row.hashinfo;
 	bucket[idx] = hash & hinfo->lhash2_mask;
 	bpf_seq_write(ctx->meta->seq, &idx, sizeof(idx));
+	bpf_seq_write(ctx->meta->seq, &sock_cookie, sizeof(sock_cookie));
+
+	return 0;
+}
+
+volatile const __u64 destroy_cookie;
+
+SEC("iter/tcp")
+int iter_tcp_destroy(struct bpf_iter__tcp *ctx)
+{
+	struct sock_common *sk_common = (struct sock_common *)ctx->sk_common;
+	__u64 sock_cookie;
+
+	if (!sk_common)
+		return 0;
+
+	sock_cookie = bpf_get_socket_cookie(sk_common);
+	if (sock_cookie != destroy_cookie)
+		return 0;
+
+	bpf_sock_destroy(sk_common);
 	bpf_seq_write(ctx->meta->seq, &sock_cookie, sizeof(sock_cookie));
 
 	return 0;
···
 	sock_cookie = bpf_get_socket_cookie(sk);
 	sk = bpf_core_cast(sk, struct sock);
 	if (sk->sk_family != sf ||
-	    sk->sk_family == AF_INET6 ?
+	    (sk->sk_family == AF_INET6 ?
 	    !ipv6_addr_loopback(&sk->sk_v6_rcv_saddr) :
-	    !ipv4_addr_loopback(sk->sk_rcv_saddr))
+	    !ipv4_addr_loopback(sk->sk_rcv_saddr)))
 		return 0;
 
 	if (sk->sk_num == ports[0])
 		idx = 0;
 	else if (sk->sk_num == ports[1])
 		idx = 1;
+	else if (!ports[0] && !ports[1])
+		idx = 0;
 	else
 		return 0;