On 12/1/20 3:44 PM, Kuniyuki Iwashima wrote: > This patch lets reuseport_detach_sock() return a pointer of struct sock, > which is used only by inet_unhash(). If it is not NULL, > inet_csk_reqsk_queue_migrate() migrates TCP_ESTABLISHED/TCP_SYN_RECV > sockets from the closing listener to the selected one. > > Listening sockets hold incoming connections as a linked list of struct > request_sock in the accept queue, and each request has reference to a full > socket and its listener. In inet_csk_reqsk_queue_migrate(), we only unlink > the requests from the closing listener's queue and relink them to the head > of the new listener's queue. We do not process each request and its > reference to the listener, so the migration completes in O(1) time > complexity. However, in the case of TCP_SYN_RECV sockets, we take special > care in the next commit. > > By default, the kernel selects a new listener randomly. In order to pick > out a different socket every time, we select the last element of socks[] as > the new listener. This behaviour is based on how the kernel moves sockets > in socks[]. (See also [1]) > > Basically, in order to redistribute sockets evenly, we have to use an eBPF > program called in the later commit, but as the side effect of such default > selection, the kernel can redistribute old requests evenly to new listeners > for a specific case where the application replaces listeners by > generations. > > For example, we call listen() for four sockets (A, B, C, D), and close the > first two by turns. The sockets move in socks[] like below. > > socks[0] : A <-. socks[0] : D socks[0] : D > socks[1] : B | => socks[1] : B <-. => socks[1] : C > socks[2] : C | socks[2] : C --' > socks[3] : D --' > > Then, if C and D have newer settings than A and B, and each socket has a > request (a, b, c, d) in their accept queue, we can redistribute old > requests evenly to new listeners. > > socks[0] : A (a) <-. socks[0] : D (a + d) socks[0] : D (a + d) > socks[1] : B (b) | => socks[1] : B (b) <-. => socks[1] : C (b + c) > socks[2] : C (c) | socks[2] : C (c) --' > socks[3] : D (d) --' > > Here, (A, D) or (B, C) can have different application settings, but they > MUST have the same settings at the socket API level; otherwise, unexpected > error may happen. For instance, if only the new listeners have > TCP_SAVE_SYN, old requests do not have SYN data, so the application will > face inconsistency and cause an error. > > Therefore, if there are different kinds of sockets, we must attach an eBPF > program described in later commits. > > Link: https://lore.kernel.org/netdev/CAEfhGiyG8Y_amDZ2C8dQoQqjZJMHjTY76b=KBkTKcBtA=dhdGQ@xxxxxxxxxxxxxx/ > Reviewed-by: Benjamin Herrenschmidt <benh@xxxxxxxxxx> > Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxxxx> > --- > include/net/inet_connection_sock.h | 1 + > include/net/sock_reuseport.h | 2 +- > net/core/sock_reuseport.c | 10 +++++++++- > net/ipv4/inet_connection_sock.c | 30 ++++++++++++++++++++++++++++++ > net/ipv4/inet_hashtables.c | 9 +++++++-- > 5 files changed, 48 insertions(+), 4 deletions(-) > > diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h > index 7338b3865a2a..2ea2d743f8fc 100644 > --- a/include/net/inet_connection_sock.h > +++ b/include/net/inet_connection_sock.h > @@ -260,6 +260,7 @@ struct dst_entry *inet_csk_route_child_sock(const struct sock *sk, > struct sock *inet_csk_reqsk_queue_add(struct sock *sk, > struct request_sock *req, > struct sock *child); > +void inet_csk_reqsk_queue_migrate(struct sock *sk, struct sock *nsk); > void inet_csk_reqsk_queue_hash_add(struct sock *sk, struct request_sock *req, > unsigned long timeout); > struct sock *inet_csk_complete_hashdance(struct sock *sk, struct sock *child, > diff --git a/include/net/sock_reuseport.h b/include/net/sock_reuseport.h > index 0e558ca7afbf..09a1b1539d4c 100644 > --- a/include/net/sock_reuseport.h > +++ b/include/net/sock_reuseport.h > @@ -31,7 +31,7 @@ struct sock_reuseport { > extern int reuseport_alloc(struct sock *sk, bool bind_inany); > extern int reuseport_add_sock(struct sock *sk, struct sock *sk2, > bool bind_inany); > -extern void reuseport_detach_sock(struct sock *sk); > +extern struct sock *reuseport_detach_sock(struct sock *sk); > extern struct sock *reuseport_select_sock(struct sock *sk, > u32 hash, > struct sk_buff *skb, > diff --git a/net/core/sock_reuseport.c b/net/core/sock_reuseport.c > index fd133516ac0e..60d7c1f28809 100644 > --- a/net/core/sock_reuseport.c > +++ b/net/core/sock_reuseport.c > @@ -216,9 +216,11 @@ int reuseport_add_sock(struct sock *sk, struct sock *sk2, bool bind_inany) > } > EXPORT_SYMBOL(reuseport_add_sock); > > -void reuseport_detach_sock(struct sock *sk) > +struct sock *reuseport_detach_sock(struct sock *sk) > { > struct sock_reuseport *reuse; > + struct bpf_prog *prog; > + struct sock *nsk = NULL; > int i; > > spin_lock_bh(&reuseport_lock); > @@ -242,8 +244,12 @@ void reuseport_detach_sock(struct sock *sk) > > reuse->num_socks--; > reuse->socks[i] = reuse->socks[reuse->num_socks]; > + prog = rcu_dereference(reuse->prog); > > if (sk->sk_protocol == IPPROTO_TCP) { > + if (reuse->num_socks && !prog) > + nsk = i == reuse->num_socks ? reuse->socks[i - 1] : reuse->socks[i]; > + > reuse->num_closed_socks++; > reuse->socks[reuse->max_socks - reuse->num_closed_socks] = sk; > } else { > @@ -264,6 +270,8 @@ void reuseport_detach_sock(struct sock *sk) > call_rcu(&reuse->rcu, reuseport_free_rcu); > out: > spin_unlock_bh(&reuseport_lock); > + > + return nsk; > } > EXPORT_SYMBOL(reuseport_detach_sock); > > diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c > index 1451aa9712b0..b27241ea96bd 100644 > --- a/net/ipv4/inet_connection_sock.c > +++ b/net/ipv4/inet_connection_sock.c > @@ -992,6 +992,36 @@ struct sock *inet_csk_reqsk_queue_add(struct sock *sk, > } > EXPORT_SYMBOL(inet_csk_reqsk_queue_add); > > +void inet_csk_reqsk_queue_migrate(struct sock *sk, struct sock *nsk) > +{ > + struct request_sock_queue *old_accept_queue, *new_accept_queue; > + > + old_accept_queue = &inet_csk(sk)->icsk_accept_queue; > + new_accept_queue = &inet_csk(nsk)->icsk_accept_queue; > + > + spin_lock(&old_accept_queue->rskq_lock); > + spin_lock(&new_accept_queue->rskq_lock); Are you sure lockdep is happy with this ? I would guess it should complain, because : lock(A); lock(B); ... unlock(B); unlock(A); will fail when the opposite action happens eventually lock(B); lock(A); ... unlock(A); unlock(B); > + > + if (old_accept_queue->rskq_accept_head) { > + if (new_accept_queue->rskq_accept_head) > + old_accept_queue->rskq_accept_tail->dl_next = > + new_accept_queue->rskq_accept_head; > + else > + new_accept_queue->rskq_accept_tail = old_accept_queue->rskq_accept_tail; > + > + new_accept_queue->rskq_accept_head = old_accept_queue->rskq_accept_head; > + old_accept_queue->rskq_accept_head = NULL; > + old_accept_queue->rskq_accept_tail = NULL; > + > + WRITE_ONCE(nsk->sk_ack_backlog, nsk->sk_ack_backlog + sk->sk_ack_backlog); > + WRITE_ONCE(sk->sk_ack_backlog, 0); > + } > + > + spin_unlock(&new_accept_queue->rskq_lock); > + spin_unlock(&old_accept_queue->rskq_lock); > +} > +EXPORT_SYMBOL(inet_csk_reqsk_queue_migrate); I fail to understand how the kernel can run fine right after this patch, before following patches are merged. All request sockets in the socket accept queue MUST have their rsk_listener set to the listener, this is how we designed things (each request socket has a reference taken on the listener) We might even have some "BUG_ON(sk != req->rsk_listener);" in some places. Since you splice list from old listener to the new one, without changing req->rsk_listener, bad things will happen. I feel the order of your patches is not correct.
