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Subject[PATCH v5 bpf-next 04/11] tcp: Add reuseport_migrate_sock() to select a new listener.
Date
reuseport_migrate_sock() does the same check done in
reuseport_listen_stop_sock(). If the reuseport group is capable of
migration, reuseport_migrate_sock() selects a new listener by the child
socket hash and increments the listener's sk_refcnt beforehand. Thus, if we
fail in the migration, we have to decrement it later.

We will support migration by eBPF in the later commits.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
---
include/net/sock_reuseport.h | 3 ++
net/core/sock_reuseport.c | 78 +++++++++++++++++++++++++++++-------
2 files changed, 67 insertions(+), 14 deletions(-)

diff --git a/include/net/sock_reuseport.h b/include/net/sock_reuseport.h
index 1333d0cddfbc..473b0b0fa4ab 100644
--- a/include/net/sock_reuseport.h
+++ b/include/net/sock_reuseport.h
@@ -37,6 +37,9 @@ extern struct sock *reuseport_select_sock(struct sock *sk,
u32 hash,
struct sk_buff *skb,
int hdr_len);
+struct sock *reuseport_migrate_sock(struct sock *sk,
+ struct sock *migrating_sk,
+ struct sk_buff *skb);
extern int reuseport_attach_prog(struct sock *sk, struct bpf_prog *prog);
extern int reuseport_detach_prog(struct sock *sk);

diff --git a/net/core/sock_reuseport.c b/net/core/sock_reuseport.c
index d5fb0ad12e87..a2bca39ec0e3 100644
--- a/net/core/sock_reuseport.c
+++ b/net/core/sock_reuseport.c
@@ -44,7 +44,7 @@ static void __reuseport_add_sock(struct sock *sk,
struct sock_reuseport *reuse)
{
reuse->socks[reuse->num_socks] = sk;
- /* paired with smp_rmb() in reuseport_select_sock() */
+ /* paired with smp_rmb() in reuseport_(select|migrate)_sock() */
smp_wmb();
reuse->num_socks++;
}
@@ -435,6 +435,23 @@ static struct sock *run_bpf_filter(struct sock_reuseport *reuse, u16 socks,
return reuse->socks[index];
}

+static struct sock *reuseport_select_sock_by_hash(struct sock_reuseport *reuse,
+ u32 hash, u16 num_socks)
+{
+ int i, j;
+
+ i = j = reciprocal_scale(hash, num_socks);
+ while (reuse->socks[i]->sk_state == TCP_ESTABLISHED) {
+ i++;
+ if (i >= num_socks)
+ i = 0;
+ if (i == j)
+ return NULL;
+ }
+
+ return reuse->socks[i];
+}
+
/**
* reuseport_select_sock - Select a socket from an SO_REUSEPORT group.
* @sk: First socket in the group.
@@ -478,19 +495,8 @@ struct sock *reuseport_select_sock(struct sock *sk,

select_by_hash:
/* no bpf or invalid bpf result: fall back to hash usage */
- if (!sk2) {
- int i, j;
-
- i = j = reciprocal_scale(hash, socks);
- while (reuse->socks[i]->sk_state == TCP_ESTABLISHED) {
- i++;
- if (i >= socks)
- i = 0;
- if (i == j)
- goto out;
- }
- sk2 = reuse->socks[i];
- }
+ if (!sk2)
+ sk2 = reuseport_select_sock_by_hash(reuse, hash, socks);
}

out:
@@ -499,6 +505,50 @@ struct sock *reuseport_select_sock(struct sock *sk,
}
EXPORT_SYMBOL(reuseport_select_sock);

+/**
+ * reuseport_migrate_sock - Select a socket from an SO_REUSEPORT group.
+ * @sk: close()ed or shutdown()ed socket in the group.
+ * @migrating_sk: ESTABLISHED/SYN_RECV full socket in the accept queue or
+ * NEW_SYN_RECV request socket during 3WHS.
+ * @skb: skb to run through BPF filter.
+ * Returns a socket (with sk_refcnt +1) that should accept the child socket
+ * (or NULL on error).
+ */
+struct sock *reuseport_migrate_sock(struct sock *sk,
+ struct sock *migrating_sk,
+ struct sk_buff *skb)
+{
+ struct sock_reuseport *reuse;
+ struct sock *nsk = NULL;
+ u16 socks;
+ u32 hash;
+
+ rcu_read_lock();
+
+ reuse = rcu_dereference(sk->sk_reuseport_cb);
+ if (!reuse)
+ goto out;
+
+ socks = READ_ONCE(reuse->num_socks);
+ if (unlikely(!socks))
+ goto out;
+
+ /* paired with smp_wmb() in __reuseport_add_sock() */
+ smp_rmb();
+
+ hash = migrating_sk->sk_hash;
+ if (sock_net(sk)->ipv4.sysctl_tcp_migrate_req)
+ nsk = reuseport_select_sock_by_hash(reuse, hash, socks);
+
+ if (nsk && unlikely(!refcount_inc_not_zero(&nsk->sk_refcnt)))
+ nsk = NULL;
+
+out:
+ rcu_read_unlock();
+ return nsk;
+}
+EXPORT_SYMBOL(reuseport_migrate_sock);
+
int reuseport_attach_prog(struct sock *sk, struct bpf_prog *prog)
{
struct sock_reuseport *reuse;
--
2.30.2
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