From: Eric Dumazet <edumazet@xxxxxxxxxx> Date: Thu, 3 Dec 2020 15:31:53 +0100 > On Thu, Dec 3, 2020 at 3:14 PM Kuniyuki Iwashima <kuniyu@xxxxxxxxxxxx> wrote: > > > > From: Eric Dumazet <eric.dumazet@xxxxxxxxx> > > Date: Tue, 1 Dec 2020 16:25:51 +0100 > > > 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); > > > > I enabled lockdep and did not see warnings of lockdep. > > > > Also, the inversion deadlock does not happen in this case. > > In reuseport_detach_sock(), sk is moved backward in socks[] and poped out > > from the eBPF map, so the old listener will not be selected as the new > > listener. > > Until the socket is closed, reallocated and used again. LOCKDEP has no > idea about soreuseport logic. > > If you run your tests long enough, lockdep should complain at some point. > > git grep -n double_lock Thank you, I will change the code like double_lock(). And I will try to continue testing lockdep without this change for curiosity!
